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Eveningness and bulimic behavior
Personality and Individual Differences 31 (2001) 361±369
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Eveningness and bulimic behavior J. Kasof * Department of Psychology and Social Behavior, School of Social Ecology, University of California, Irvine, CA 92697, USA Received 11 January 2000; received in revised form 23 June 2000; accepted 19 July 2000
Abstract Previous research suggests that evening constitutes a high-risk environment that increases the probability of binge eating and purging. Individual dierences in morningness±eveningness are associated with diering levels of exposure to evening versus day, with ``night people'' spending a larger portion of their waking lives during the evening and a smaller portion of their waking lives during the day than do ``day people''. This study tested the hypothesis that greater eveningness is associated with greater binging and purging. One-hundred and ®fty-one undergraduates completed the Composite Scale of Morningness±Eveningness, the Bulimia Test-Revised, the Bulimia Scale of the Eating Disorders Inventory, and measures of several other variables. Results showed that eveningness was correlated moderately and positively (rs=0.24) with both measures of bulimic behavior; these correlations were reduced only slightly after controlling for other study variables. It is argued that exposure to the dimmer lighting of evening promotes general behavioral disinhibition, thus undermining self-regulatory control and adherence to one's dietary standards, resulting in the disinhibited eating that is the hallmark of bulimia. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Binge eating; Bulimia; Circadian rhythms; Morningness±eveningness; Self-regulation
1. Introduction Several lines of evidence suggest that exposure to the dim light of evening may increase the probability of binge eating and purging. First, both binge eating and purging are substantially more probable in the evening than during the day, independent of setting, occupation, and day of the week (Bulik et al., 1992; de Zwaan, Nutzinger & Schoenbeck, 1992; Johnson, Schlundt, Barclay, Carr-Nangle & Engler, 1995; Mitchell, Pyle, & Fletcher, 1991; Mitchell, Hatsukami, Eckert & Pyle, 1985; Schlundt, Johnson & Jarrell, 1985, 1986). Second, both binging and purging are * Tel.: +1-949-824-6849; fax: +1-949-824-3002. E-mail address: [email protected] 0191-8869/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0191-8869(00)00142-2
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more frequent in months that have longer nights than in months that have shorter nights (Blouin et al., 1992; Fornari, Sandberg, Lachermeyer, Cohen, Matthews & Montero, 1989; Lam, Goldner & Grewal, 1996; Levitan, Kaplan, Levitt & Joe, 1994). Third, the tendency to eat in the evening is more prevalent among individuals who binge frequently than among weight-matched controls (e.g. Greeno, Wing & Marcus, 1995; Rand, Macgregor, & Stunkard, 1997). Fourth, bulimia nervosa has been associated with later times of going to sleep and awakening (Latzer, Tzischinsky, Epstein, Klein & Peretz, 1999). Fifth, among restrained eaters, bulimic behavior is associated with self-reported use of dimmer light while eating (Kasof, 2000a). Individual dierences in the amount of one's waking hours that are spent during evening rather than day are in¯uenced by circadian rhythm. The term morningness±eveningness (hereafter shortened to eveningness) is used to describe stable individual dierences in usual times of sleep onset, awakening, alertness, and activity (Tankova, Adan & Buela-Casal, 1994). Individuals who are high in eveningness generally stay up later into the night before going to sleep and wake up later in the morning than do individuals who are low in eveningness. Hence, so-called ``night people'' spend a larger portion of their waking lives during the evening and a smaller portion of their waking lives during the day than do ``day people''. If eveningness increases the amount of one's waking hours that are spent during the evening rather than day, and if evening constitutes a high-risk environment that increases the probability of binging and purging, then it logically follows that eveningness should increase the probability of binging and purging. That is, just as binging and purging occur more frequently in the evening than during the day, and just as they occur more frequently in months that have longer evenings than in months that have shorter evenings, so binging and purging should occur more frequently in people who are high in eveningness than in those who are low in eveningness. This hypothesis is consistent with a recent study by Latzer et al. (1999), who used ambulatory actigraphic monitoring to assess sleep±wake patterns in bulimic patients and control participants. Although the two groups did not dier in sleep latency, sleep eciency, or length of sleep, the bulimic patients' mean times of sleep onset and waking were approximately 1 h later than those of the control participants (adjusting for occupational and marital status, age, and presence of children). However, although Latzer et al.'s results are consistent with the notion that greater eveningness increases the risk of binging or purging, the study was marred by several serious methodological ¯aws and limitations. First, unexplained inconsistencies in reporting make the study dicult to interpret. For example, although the abstract reported sample sizes of 29 bulimic patients and 18 control participants, the text reported samples of 34 bulimics and 18 controls (p. 316), and a table reported samples of 25 bulimics and 21 controls (p. 317). Second, regardless of which of these numbers was correct, the study used very small samples; hence, there is a need for replication with larger samples. Third, the study was limited to clinically signi®cant bulimia nervosa and thus left unaddressed the question of whether eveningness is associated with bulimic symptomatology less extreme in severity (e.g. subclinical binging). Fourth, the bulimic sample was limited to females, thus leaving unaddressed whether the ®ndings were gender-speci®c. Finally, no information was provided as to how control participants were selected, the gender composition of the control group, and so forth. The study to be reported herein expanded on Latzer et al.'s (1999) study in several ways. Questionnaire measures of eveningness and bulimic behavior were administered to an undergraduate sample that was considerably larger than in the Latzer et al. study, included both female
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and male participants, and contained virtually no participants who had bulimic symptoms so severe as to warrant clinical diagnosis. Additionally, although previous studies using questionnaire measures of eveningness have not attempted to determine whether such measures are contaminated by socially desirable response bias, such bias was measured in the present study for possible use as a covariate because ``night people'' are generally regarded less positively than are ``day people'' (Hepburn, Ortiz & Locksley, 1984; Locksley, Hepburn & Ortiz, 1982). Moreover, because depression, impulsiveness, and arousability may correlate with eveningness (Chelminski, Ferraro, Petros & Plaud, 1999; Drennan, Klauber, Kripke & Goyette, 1991; Matthews, 1988; Mecacci & Rocchetti, 1998; Mehrabian & Riccioni, 1986; Mehrabian, Nahum & Duke, 1985± 1986; Wilson, 1990) and with bulimic symptomatology (e.g. Garner, 1991; Lee, Rush & Mitchell, 1985; Mehrabian & Riccioni; Mehrabian et al.; Phelps & Wilczenski, 1993), these variables were measured as possible covariates in the present study. 2. Method 2.1. Participants Participants were 151 undergraduates (57 males, 94 females) who received extra credit in an introductory course in social psychology. The mean age of the sample was 22.7 (S.D.=4.9; range=18±49). Most participants (75.0%) were Caucasian; 11.5% were Hispanic, 8.1% were Asian, and 5.4% were African-American. The mean body mass index (BMI; self-reported weight in kilograms divided by the square of self-reported height in meters) was 22.46 (S.D.=3.27; range=16±33); 30 participants (20%; nine females and 21 males) had a BMI higher than 25.0, which is conventionally considered overweight, and 19 participants (12.7%; 17 females and two males) had a BMI lower than 19.0, which is conventionally considered underweight. 2.2. Procedure and measures In the ®rst week of classes, 134 students (51 males, 83 females) completed questionnaire measures of eveningness, bulimic behavior, socially desirable response bias, impulsivity, and arousability. One week later, 123 students (46 males, 77 females) completed measures of depression and bulimic behavior. In both weeks, the questionnaires used in this study were presented along with other questionnaires that were used in an unrelated study. One-hundred and six students (40 males, 66 females) attended both sessions. All responses were anonymous; participants were identi®ed only by code numbers. Eveningness was measured with Smith, Reilly and Midki's (1989) 13-item Composite Scale. Using a Likert-type format, participants responded to questions about their chronically preferred times for going to bed, waking up, working, and taking tests, and about their characteristic levels of alertness at dierent times. In previous research, the Composite Scale reliably and validly measured relative bedtime preferences and self-reported times of going to bed, awakening, and studying (Greenwood, 1994; Guthrie, Ash & Bendapudi, 1995; Pornpitakpan, 2000; Roberts & Kyllonen, 1999; Smith et al.). The scale was calculated so that higher scores indicate greater eveningness. The alpha coecient for the Composite Scale was 0.89 in the present study.
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Bulimic behavior was measured with two widely used questionnaires. The Bulimia Scale of the Eating Disorders Inventory (Garner Olmstead & Polivy, 1983) contains seven statements that express a tendency to think about and to engage in binge eating (e.g. ``I have gone on eating binges where I felt that I could not stop''). Participants indicated how frequently they engaged in the given behavior, using a range of 1 (never) to 6 (always). The Bulimia Scale has been found to be reliable and valid both in clinical and nonclinical samples (Garner, 1991). In the present study, the alpha coecient was 0.85. The Bulimia Scale was administered in the ®rst data-collection session. The Bulimia Test-Revised (BULIT-R; Thelen, Farmer, Wonderlich & Smith, 1991) contains 28 items concerned primarily with binge eating, although several items also tap purging and concern about weight and body shape. Research supports the reliability and validity of the BULIT-R (e.g. Brelsford, Hummel & Barrios, 1992; Welch, Thompson & Hall, 1993). (The BULIT-R was originally developed only with female participants; to make it appropriate for participants of either sex, the item ``Compared with women your age, how preoccupied are you about your weight and body shape?'' was edited to read ``Compared with other people your age, how preoccupied are you about your weight and body shape?'') In the present study, only three participants (2%) scored higher than 104 or 98, the maximally discriminant cuto scores for diagnosing bulimia nervosa according to Thelen et al. and Welch et al., respectively. The alpha coecient for the BULIT-R was 0.95 in the present study. The BULIT-R was administered in the second data-collection session. The Bulimia Scale and the BULIT-R were highly correlated in the present study, r=0.77, P<.0001. Other variables included socially desirable response bias, which was measured with the Impression Management Scale (IM, Paulhus, 1991; coecient alpha in the present study=0.80); depression, which was measured with the revised Beck Depression Inventory (BDI; Beckham & Leber, 1985; alpha=0.88) and the Automatic Thoughts Questionnaire (ATQ; Hollon & Kendall, 1980; alpha=0.97; the two measures of depression were highly correlated, r[122]=0.84, P<0.0001), arousability, which was measured with the Stimulus Screening Scale (SSS; Mehrahian, 1977; alpha=0.92); and impulsivity, which was measured with the Impulse Regulation Scale of the EDI-2 (Eating Disorders Inventory) (IR; Garner, 1991; alpha=0.80). 3. Results Because correlations did not dier signi®cantly between the sexes, data for both sexes were combined in the analyses reported below. Tests of signi®cance were one-tailed for analyses correlating eveningness with bulimic behavior because the direction of these hypotheses was predicted; all other tests were two-tailed. Results are consistent with the hypothesis that greater eveningness is associated with greater risk of bulimic behavior. As shown in Table 1, eveningness correlated positively with both the BULIT-R, r(106)=0.24, P=0.006, and the Bulimia Scale, r(134)=0.24, P=0.002. Socially desirable response bias correlated signi®cantly with both eveningness and bulimia, as did other variables (Table 1). After statistically controlling for socially desirable response bias, depression, impulsivity, and arousability, eveningness still correlated positively and signi®cantly with the BULIT-R (partial r=0.20, P=0.03) and correlated marginally with the Bulimia Scale (partial r=0.14, P=0.09).
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Although the main purpose of this study was to assess the relationship between eveningness and bulimic behavior, the data also provided information pertinent to gender dierences. As noted already, correlations between study variables did not dier signi®cantly between males and females. Yet the mean values for most variables diverged signi®cantly between the sexes. Females scored signi®cantly higher than males on the BULIT-R (Ms=52.7 and 42.9, t=2.87, P=0.005), the Bulimia Scale (Ms=13.6 and 11.4, t=2.62, P=0.01), the SSS (Ms=17.8 and 2.10, t=3.49, P=0.0007), and the IM scale (Ms=5.57 and 4.16, t=2.16, P=0.03). Males scored signi®cantly higher than females on IR (Ms=27.3 and 24.2, t=2.50, P=0.01). The sexes did not dier signi®cantly on eveningness (Ms=37.16 for males and 39.47 for females, t=1.73), the BDI (Ms=7.56 for males and 8.39 for females, t=0.61), or the ATQ (Ms=57.31 for males and 59.36 for females, t=0.47). 4. Discussion This study found that greater eveningness was moderately associated with greater bulimic behavior in a nonclinical sample of undergraduates. This ®nding replicates and expands upon Latzer et al.'s (1999) ®nding that mean times of sleep onset and of awakening were about 1 h later in female bulimia nervosa patients than in control participants. These studies, taken together with other research that found bulimic behavior to be more probable during evening than day (e.g. Schlundt et al., 1985, 1986), during months that have longer nights than in those that have shorter nights (e.g. Blouin et al., 1992), and in individuals who eat in the evening rather than earlier in the day (e.g. Rand et al., 1997), suggest that evening is a high-risk environment in which bulimic behavior is more likely. The present study has several limitations that can be addressed in future research. The correlational design of this study does not permit conclusions about causality: the positive correlation between eveningness and bulimic behavior may result from eveningness promoting bulimic behavior, from Table 1 Correlations between study variablesa
1. BULIT-R 2. Bulimia Scale 3. Eveningness 4. IM 5. BDI 6. ATQ 7. Impulsivity 8. Arousability a
1
2
3
77d 24c 22c 22b 14 17 27d
24d 8b 33d 26c 33d 32d
21c 10 09 23c 19b
4
33d 32d 36d 30d
5
6
7
84d 45d 27c
44d 22b
36d
Decimal points are removed. BULIT-R, Bulimia Test-Revised; IM, Impression Management; BDI, Beck Depression Inventory; ATQ, Automatic Thoughts Questionnaire. b P<0.05 c P<0.01 d P40.005
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bulimic behavior promoting eveningness, or from a spurious correlation with some unmeasured variable. One possibility, for example, is that binging or purging may keep one out of bed longer, thus promoting greater eveningness. However, because the measure of eveningness used in this study assesses preference for times of waking, retiring, and participating in activities, it seems implausible that the time-consuming and distressing behaviors of binging and purging can plausibly increase eveningness. In order to determine causality, experimental research is needed in which participants are randomly assigned to earlier versus later bedtimes (e.g. shiftworkers could be randomly assigned to night shift or day shift and then monitored for buliniic behavior). Additionally, although the self-report instruments used in this study have proven valid and reliable in previous studies, greater con®dence in the ®ndings would come from replications that use observational measures. There are several possible explanations for why bulimic behavior is associated with eveningness and, more generally, with evening. One possibility concerns the temporal distribution of solitude: being alone increases the probability of binging and purging (e.g. Herman, Polivy & Silver, 1979; Schlundt et al., 1985, 1986); hence if students socialize more during the day than evening, it is possible that eveningness is associated with bulimic behavior because ``night people'' may spend more of their waking hours in solitude than do ``day people''. Another possibility is that exposure to the bright light of day decreases the frequency of binging or purging even after such exposure. If Braun, Sunday, Fornari and Halmi's (1999) ®nding that bright light therapy decreased binge frequency in clinically bulimic women during winter extends to nonclinical students of both sexes, and to levels of illumination lower than that used in bright light therapy (10,000 lux), then this may provide an explanation for the results of the present study. The relationship between eveningness and bulimic behavior can also be explained in terms of the theoretical framework proposed by Kasof (2000a,b). According to Kasof, exposure to dimmer lighting promotes general behavioral disinhibition, thus undermining self-regulatory control and adherence to one's dietary standards. Dimly lit settings increase the probability of counter-normative behaviors that are more successfully inhibited under brighter lightning (Gergen, Gergen & Barton, 1973; Kinsey, Pomeroy, Martin & Gebhard, 1953; Page & Moss, 1976). These and other counter-normative behaviors are also particularly more probable during evening than day (Mann, 1969, 1981; Melbin, 1987), possibly because of the lower level of indoor illuminance generally present during evening than during day. Kasof further argued that the disinhibiting eect of dimmer light is mediated by diminished self-awareness, the state form of self-focused attention. That dimmer lighting reduces self-awareness was demonstrated by Giord (1988): expecting to ®nd that dimmer lighting promotes intimate self-disclosure, Giord asked undergraduate students to write letters about themselves to their friends, and he randomly assigned the students to write these letters while alone in a room that was illuminated either brightly or dimly. Students who were assigned to the dimmer condition spent less time writing about themselves, wrote less highly self-disclosing letters, and used fewer words and fewer selfreferential words (e.g. I, me, mine, myself) than did students who were assigned to the brighter condition. Although Giord did not anticipate this outcome and did not interpret his results in terms of self-awareness, these dependent variables are well-validated indicators of heightened selffocused attention (e.g. Davis & Brock, 1975; Hull, Levenson, Young & Sher, 1983; Ickes, Layden, & Barnes, 1978; Schaller, 1997). Thus, existing evidence demonstrates that exposure to dimmer lighting decreases self-awareness, at least in a nonsocial indoor situation.
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Research has found that self-awareness promotes self-regulatory control and adherence to salient behavioral standards (Carver & Scheier, 1998). In particular, adherence to one's dietary standards is undermined when self-awareness is diminished, and such adherence is maintained or strengthened when self-awareness is increased (e.g. Heatherton, Polivy, Herman, & Baumeister, 1993; Pliner & Iuppa, 1978; Sentyrz & Bushman, 1998). That exposure to dimmer light decreases self-awareness thus oers a parsimonious explanation of why dimmer light promotes disinhibition not only of counter-normative behaviors performed in social situations (e.g. Gergen et al., 1973; Mann, 1981; Page & Moss, 1976) but also counter-normative behaviors typically performed in the absence of others Ð behaviors such as binge eating and purging. Finally, this explanation of the present results suggests new directions for future research. Although binging is de®ned in part by the quantity of food consumed, the disinhibition theory also predicts that adherence to qualitative norms for eating may be aected by eveningness. For example, among vegetarians who enjoy the taste of meat but who strive to avoid it because of ethical, religious, or health concerns, is the temptation to deviate from the vegetarian diet resisted less successfully in the evening than during the day? In such persons, does eveningness promote departures from the vegetarian diet? Does eveningness also promote substance abuse among people who strive to inhibit such use? For example, among recovering alcoholics, former drug addicts, and former smokers, does eveningness increase the probability of relapse? Does eveningness aect rates of relapse among recovered bulimics? Are therapeutic treatments for bulimia less eective in patients who are higher in eveningness? Are such treatments more eective when undertaken in months that have shorter nights than in those that have longer nights? Can making one's usual bedtime earlier help reduce bulimic behavior? The answers to these and related questions may improve the eectiveness of therapeutic eorts in the future.
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Eveningness and bulimic behavior J. Kasof * Department of Psychology and Social Behavior, School of Social Ecology, University of California, Irvine, CA 92697, USA Received 11 January 2000; received in revised form 23 June 2000; accepted 19 July 2000
Abstract Previous research suggests that evening constitutes a high-risk environment that increases the probability of binge eating and purging. Individual dierences in morningness±eveningness are associated with diering levels of exposure to evening versus day, with ``night people'' spending a larger portion of their waking lives during the evening and a smaller portion of their waking lives during the day than do ``day people''. This study tested the hypothesis that greater eveningness is associated with greater binging and purging. One-hundred and ®fty-one undergraduates completed the Composite Scale of Morningness±Eveningness, the Bulimia Test-Revised, the Bulimia Scale of the Eating Disorders Inventory, and measures of several other variables. Results showed that eveningness was correlated moderately and positively (rs=0.24) with both measures of bulimic behavior; these correlations were reduced only slightly after controlling for other study variables. It is argued that exposure to the dimmer lighting of evening promotes general behavioral disinhibition, thus undermining self-regulatory control and adherence to one's dietary standards, resulting in the disinhibited eating that is the hallmark of bulimia. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Binge eating; Bulimia; Circadian rhythms; Morningness±eveningness; Self-regulation
1. Introduction Several lines of evidence suggest that exposure to the dim light of evening may increase the probability of binge eating and purging. First, both binge eating and purging are substantially more probable in the evening than during the day, independent of setting, occupation, and day of the week (Bulik et al., 1992; de Zwaan, Nutzinger & Schoenbeck, 1992; Johnson, Schlundt, Barclay, Carr-Nangle & Engler, 1995; Mitchell, Pyle, & Fletcher, 1991; Mitchell, Hatsukami, Eckert & Pyle, 1985; Schlundt, Johnson & Jarrell, 1985, 1986). Second, both binging and purging are * Tel.: +1-949-824-6849; fax: +1-949-824-3002. E-mail address: [email protected] 0191-8869/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0191-8869(00)00142-2
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more frequent in months that have longer nights than in months that have shorter nights (Blouin et al., 1992; Fornari, Sandberg, Lachermeyer, Cohen, Matthews & Montero, 1989; Lam, Goldner & Grewal, 1996; Levitan, Kaplan, Levitt & Joe, 1994). Third, the tendency to eat in the evening is more prevalent among individuals who binge frequently than among weight-matched controls (e.g. Greeno, Wing & Marcus, 1995; Rand, Macgregor, & Stunkard, 1997). Fourth, bulimia nervosa has been associated with later times of going to sleep and awakening (Latzer, Tzischinsky, Epstein, Klein & Peretz, 1999). Fifth, among restrained eaters, bulimic behavior is associated with self-reported use of dimmer light while eating (Kasof, 2000a). Individual dierences in the amount of one's waking hours that are spent during evening rather than day are in¯uenced by circadian rhythm. The term morningness±eveningness (hereafter shortened to eveningness) is used to describe stable individual dierences in usual times of sleep onset, awakening, alertness, and activity (Tankova, Adan & Buela-Casal, 1994). Individuals who are high in eveningness generally stay up later into the night before going to sleep and wake up later in the morning than do individuals who are low in eveningness. Hence, so-called ``night people'' spend a larger portion of their waking lives during the evening and a smaller portion of their waking lives during the day than do ``day people''. If eveningness increases the amount of one's waking hours that are spent during the evening rather than day, and if evening constitutes a high-risk environment that increases the probability of binging and purging, then it logically follows that eveningness should increase the probability of binging and purging. That is, just as binging and purging occur more frequently in the evening than during the day, and just as they occur more frequently in months that have longer evenings than in months that have shorter evenings, so binging and purging should occur more frequently in people who are high in eveningness than in those who are low in eveningness. This hypothesis is consistent with a recent study by Latzer et al. (1999), who used ambulatory actigraphic monitoring to assess sleep±wake patterns in bulimic patients and control participants. Although the two groups did not dier in sleep latency, sleep eciency, or length of sleep, the bulimic patients' mean times of sleep onset and waking were approximately 1 h later than those of the control participants (adjusting for occupational and marital status, age, and presence of children). However, although Latzer et al.'s results are consistent with the notion that greater eveningness increases the risk of binging or purging, the study was marred by several serious methodological ¯aws and limitations. First, unexplained inconsistencies in reporting make the study dicult to interpret. For example, although the abstract reported sample sizes of 29 bulimic patients and 18 control participants, the text reported samples of 34 bulimics and 18 controls (p. 316), and a table reported samples of 25 bulimics and 21 controls (p. 317). Second, regardless of which of these numbers was correct, the study used very small samples; hence, there is a need for replication with larger samples. Third, the study was limited to clinically signi®cant bulimia nervosa and thus left unaddressed the question of whether eveningness is associated with bulimic symptomatology less extreme in severity (e.g. subclinical binging). Fourth, the bulimic sample was limited to females, thus leaving unaddressed whether the ®ndings were gender-speci®c. Finally, no information was provided as to how control participants were selected, the gender composition of the control group, and so forth. The study to be reported herein expanded on Latzer et al.'s (1999) study in several ways. Questionnaire measures of eveningness and bulimic behavior were administered to an undergraduate sample that was considerably larger than in the Latzer et al. study, included both female
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and male participants, and contained virtually no participants who had bulimic symptoms so severe as to warrant clinical diagnosis. Additionally, although previous studies using questionnaire measures of eveningness have not attempted to determine whether such measures are contaminated by socially desirable response bias, such bias was measured in the present study for possible use as a covariate because ``night people'' are generally regarded less positively than are ``day people'' (Hepburn, Ortiz & Locksley, 1984; Locksley, Hepburn & Ortiz, 1982). Moreover, because depression, impulsiveness, and arousability may correlate with eveningness (Chelminski, Ferraro, Petros & Plaud, 1999; Drennan, Klauber, Kripke & Goyette, 1991; Matthews, 1988; Mecacci & Rocchetti, 1998; Mehrabian & Riccioni, 1986; Mehrabian, Nahum & Duke, 1985± 1986; Wilson, 1990) and with bulimic symptomatology (e.g. Garner, 1991; Lee, Rush & Mitchell, 1985; Mehrabian & Riccioni; Mehrabian et al.; Phelps & Wilczenski, 1993), these variables were measured as possible covariates in the present study. 2. Method 2.1. Participants Participants were 151 undergraduates (57 males, 94 females) who received extra credit in an introductory course in social psychology. The mean age of the sample was 22.7 (S.D.=4.9; range=18±49). Most participants (75.0%) were Caucasian; 11.5% were Hispanic, 8.1% were Asian, and 5.4% were African-American. The mean body mass index (BMI; self-reported weight in kilograms divided by the square of self-reported height in meters) was 22.46 (S.D.=3.27; range=16±33); 30 participants (20%; nine females and 21 males) had a BMI higher than 25.0, which is conventionally considered overweight, and 19 participants (12.7%; 17 females and two males) had a BMI lower than 19.0, which is conventionally considered underweight. 2.2. Procedure and measures In the ®rst week of classes, 134 students (51 males, 83 females) completed questionnaire measures of eveningness, bulimic behavior, socially desirable response bias, impulsivity, and arousability. One week later, 123 students (46 males, 77 females) completed measures of depression and bulimic behavior. In both weeks, the questionnaires used in this study were presented along with other questionnaires that were used in an unrelated study. One-hundred and six students (40 males, 66 females) attended both sessions. All responses were anonymous; participants were identi®ed only by code numbers. Eveningness was measured with Smith, Reilly and Midki's (1989) 13-item Composite Scale. Using a Likert-type format, participants responded to questions about their chronically preferred times for going to bed, waking up, working, and taking tests, and about their characteristic levels of alertness at dierent times. In previous research, the Composite Scale reliably and validly measured relative bedtime preferences and self-reported times of going to bed, awakening, and studying (Greenwood, 1994; Guthrie, Ash & Bendapudi, 1995; Pornpitakpan, 2000; Roberts & Kyllonen, 1999; Smith et al.). The scale was calculated so that higher scores indicate greater eveningness. The alpha coecient for the Composite Scale was 0.89 in the present study.
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Bulimic behavior was measured with two widely used questionnaires. The Bulimia Scale of the Eating Disorders Inventory (Garner Olmstead & Polivy, 1983) contains seven statements that express a tendency to think about and to engage in binge eating (e.g. ``I have gone on eating binges where I felt that I could not stop''). Participants indicated how frequently they engaged in the given behavior, using a range of 1 (never) to 6 (always). The Bulimia Scale has been found to be reliable and valid both in clinical and nonclinical samples (Garner, 1991). In the present study, the alpha coecient was 0.85. The Bulimia Scale was administered in the ®rst data-collection session. The Bulimia Test-Revised (BULIT-R; Thelen, Farmer, Wonderlich & Smith, 1991) contains 28 items concerned primarily with binge eating, although several items also tap purging and concern about weight and body shape. Research supports the reliability and validity of the BULIT-R (e.g. Brelsford, Hummel & Barrios, 1992; Welch, Thompson & Hall, 1993). (The BULIT-R was originally developed only with female participants; to make it appropriate for participants of either sex, the item ``Compared with women your age, how preoccupied are you about your weight and body shape?'' was edited to read ``Compared with other people your age, how preoccupied are you about your weight and body shape?'') In the present study, only three participants (2%) scored higher than 104 or 98, the maximally discriminant cuto scores for diagnosing bulimia nervosa according to Thelen et al. and Welch et al., respectively. The alpha coecient for the BULIT-R was 0.95 in the present study. The BULIT-R was administered in the second data-collection session. The Bulimia Scale and the BULIT-R were highly correlated in the present study, r=0.77, P<.0001. Other variables included socially desirable response bias, which was measured with the Impression Management Scale (IM, Paulhus, 1991; coecient alpha in the present study=0.80); depression, which was measured with the revised Beck Depression Inventory (BDI; Beckham & Leber, 1985; alpha=0.88) and the Automatic Thoughts Questionnaire (ATQ; Hollon & Kendall, 1980; alpha=0.97; the two measures of depression were highly correlated, r[122]=0.84, P<0.0001), arousability, which was measured with the Stimulus Screening Scale (SSS; Mehrahian, 1977; alpha=0.92); and impulsivity, which was measured with the Impulse Regulation Scale of the EDI-2 (Eating Disorders Inventory) (IR; Garner, 1991; alpha=0.80). 3. Results Because correlations did not dier signi®cantly between the sexes, data for both sexes were combined in the analyses reported below. Tests of signi®cance were one-tailed for analyses correlating eveningness with bulimic behavior because the direction of these hypotheses was predicted; all other tests were two-tailed. Results are consistent with the hypothesis that greater eveningness is associated with greater risk of bulimic behavior. As shown in Table 1, eveningness correlated positively with both the BULIT-R, r(106)=0.24, P=0.006, and the Bulimia Scale, r(134)=0.24, P=0.002. Socially desirable response bias correlated signi®cantly with both eveningness and bulimia, as did other variables (Table 1). After statistically controlling for socially desirable response bias, depression, impulsivity, and arousability, eveningness still correlated positively and signi®cantly with the BULIT-R (partial r=0.20, P=0.03) and correlated marginally with the Bulimia Scale (partial r=0.14, P=0.09).
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Although the main purpose of this study was to assess the relationship between eveningness and bulimic behavior, the data also provided information pertinent to gender dierences. As noted already, correlations between study variables did not dier signi®cantly between males and females. Yet the mean values for most variables diverged signi®cantly between the sexes. Females scored signi®cantly higher than males on the BULIT-R (Ms=52.7 and 42.9, t=2.87, P=0.005), the Bulimia Scale (Ms=13.6 and 11.4, t=2.62, P=0.01), the SSS (Ms=17.8 and 2.10, t=3.49, P=0.0007), and the IM scale (Ms=5.57 and 4.16, t=2.16, P=0.03). Males scored signi®cantly higher than females on IR (Ms=27.3 and 24.2, t=2.50, P=0.01). The sexes did not dier signi®cantly on eveningness (Ms=37.16 for males and 39.47 for females, t=1.73), the BDI (Ms=7.56 for males and 8.39 for females, t=0.61), or the ATQ (Ms=57.31 for males and 59.36 for females, t=0.47). 4. Discussion This study found that greater eveningness was moderately associated with greater bulimic behavior in a nonclinical sample of undergraduates. This ®nding replicates and expands upon Latzer et al.'s (1999) ®nding that mean times of sleep onset and of awakening were about 1 h later in female bulimia nervosa patients than in control participants. These studies, taken together with other research that found bulimic behavior to be more probable during evening than day (e.g. Schlundt et al., 1985, 1986), during months that have longer nights than in those that have shorter nights (e.g. Blouin et al., 1992), and in individuals who eat in the evening rather than earlier in the day (e.g. Rand et al., 1997), suggest that evening is a high-risk environment in which bulimic behavior is more likely. The present study has several limitations that can be addressed in future research. The correlational design of this study does not permit conclusions about causality: the positive correlation between eveningness and bulimic behavior may result from eveningness promoting bulimic behavior, from Table 1 Correlations between study variablesa
1. BULIT-R 2. Bulimia Scale 3. Eveningness 4. IM 5. BDI 6. ATQ 7. Impulsivity 8. Arousability a
1
2
3
77d 24c 22c 22b 14 17 27d
24d 8b 33d 26c 33d 32d
21c 10 09 23c 19b
4
33d 32d 36d 30d
5
6
7
84d 45d 27c
44d 22b
36d
Decimal points are removed. BULIT-R, Bulimia Test-Revised; IM, Impression Management; BDI, Beck Depression Inventory; ATQ, Automatic Thoughts Questionnaire. b P<0.05 c P<0.01 d P40.005
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bulimic behavior promoting eveningness, or from a spurious correlation with some unmeasured variable. One possibility, for example, is that binging or purging may keep one out of bed longer, thus promoting greater eveningness. However, because the measure of eveningness used in this study assesses preference for times of waking, retiring, and participating in activities, it seems implausible that the time-consuming and distressing behaviors of binging and purging can plausibly increase eveningness. In order to determine causality, experimental research is needed in which participants are randomly assigned to earlier versus later bedtimes (e.g. shiftworkers could be randomly assigned to night shift or day shift and then monitored for buliniic behavior). Additionally, although the self-report instruments used in this study have proven valid and reliable in previous studies, greater con®dence in the ®ndings would come from replications that use observational measures. There are several possible explanations for why bulimic behavior is associated with eveningness and, more generally, with evening. One possibility concerns the temporal distribution of solitude: being alone increases the probability of binging and purging (e.g. Herman, Polivy & Silver, 1979; Schlundt et al., 1985, 1986); hence if students socialize more during the day than evening, it is possible that eveningness is associated with bulimic behavior because ``night people'' may spend more of their waking hours in solitude than do ``day people''. Another possibility is that exposure to the bright light of day decreases the frequency of binging or purging even after such exposure. If Braun, Sunday, Fornari and Halmi's (1999) ®nding that bright light therapy decreased binge frequency in clinically bulimic women during winter extends to nonclinical students of both sexes, and to levels of illumination lower than that used in bright light therapy (10,000 lux), then this may provide an explanation for the results of the present study. The relationship between eveningness and bulimic behavior can also be explained in terms of the theoretical framework proposed by Kasof (2000a,b). According to Kasof, exposure to dimmer lighting promotes general behavioral disinhibition, thus undermining self-regulatory control and adherence to one's dietary standards. Dimly lit settings increase the probability of counter-normative behaviors that are more successfully inhibited under brighter lightning (Gergen, Gergen & Barton, 1973; Kinsey, Pomeroy, Martin & Gebhard, 1953; Page & Moss, 1976). These and other counter-normative behaviors are also particularly more probable during evening than day (Mann, 1969, 1981; Melbin, 1987), possibly because of the lower level of indoor illuminance generally present during evening than during day. Kasof further argued that the disinhibiting eect of dimmer light is mediated by diminished self-awareness, the state form of self-focused attention. That dimmer lighting reduces self-awareness was demonstrated by Giord (1988): expecting to ®nd that dimmer lighting promotes intimate self-disclosure, Giord asked undergraduate students to write letters about themselves to their friends, and he randomly assigned the students to write these letters while alone in a room that was illuminated either brightly or dimly. Students who were assigned to the dimmer condition spent less time writing about themselves, wrote less highly self-disclosing letters, and used fewer words and fewer selfreferential words (e.g. I, me, mine, myself) than did students who were assigned to the brighter condition. Although Giord did not anticipate this outcome and did not interpret his results in terms of self-awareness, these dependent variables are well-validated indicators of heightened selffocused attention (e.g. Davis & Brock, 1975; Hull, Levenson, Young & Sher, 1983; Ickes, Layden, & Barnes, 1978; Schaller, 1997). Thus, existing evidence demonstrates that exposure to dimmer lighting decreases self-awareness, at least in a nonsocial indoor situation.
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Research has found that self-awareness promotes self-regulatory control and adherence to salient behavioral standards (Carver & Scheier, 1998). In particular, adherence to one's dietary standards is undermined when self-awareness is diminished, and such adherence is maintained or strengthened when self-awareness is increased (e.g. Heatherton, Polivy, Herman, & Baumeister, 1993; Pliner & Iuppa, 1978; Sentyrz & Bushman, 1998). That exposure to dimmer light decreases self-awareness thus oers a parsimonious explanation of why dimmer light promotes disinhibition not only of counter-normative behaviors performed in social situations (e.g. Gergen et al., 1973; Mann, 1981; Page & Moss, 1976) but also counter-normative behaviors typically performed in the absence of others Ð behaviors such as binge eating and purging. Finally, this explanation of the present results suggests new directions for future research. Although binging is de®ned in part by the quantity of food consumed, the disinhibition theory also predicts that adherence to qualitative norms for eating may be aected by eveningness. For example, among vegetarians who enjoy the taste of meat but who strive to avoid it because of ethical, religious, or health concerns, is the temptation to deviate from the vegetarian diet resisted less successfully in the evening than during the day? In such persons, does eveningness promote departures from the vegetarian diet? Does eveningness also promote substance abuse among people who strive to inhibit such use? For example, among recovering alcoholics, former drug addicts, and former smokers, does eveningness increase the probability of relapse? Does eveningness aect rates of relapse among recovered bulimics? Are therapeutic treatments for bulimia less eective in patients who are higher in eveningness? Are such treatments more eective when undertaken in months that have shorter nights than in those that have longer nights? Can making one's usual bedtime earlier help reduce bulimic behavior? The answers to these and related questions may improve the eectiveness of therapeutic eorts in the future.
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