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The restraint scale: A psychometric investigation
Brhar. Res. Ther. Vol. 21, No. 3. pp. 253-258, Printed in Great Britain
THE
1983
OOOS-7967/83/030253-06$03.00/O Pergamon Press Ltd
RESTRAINT SCALE: A PSYCHOMETRIC INVESTIGATION AUDREY
University
of Illinois at Chicago
Circle, Department
J.
RUDERMAN of Psychology,
(Receioed 21 September
Box 4348, Chicago,
IL 60680, U.S.A.
1982)
Summary-The psychometric characteristics of the Restraint Scale in obese and normal-weight subjects were compared. Scores were significantly higher and more homogeneous in the obese than in the normal-weight group. In light of previous studies indicating that obese subjects behave like normal-weight subjects whose Restraint scores are several points (approx. 3-6) lower, the present result was interpreted as suggesting that numerically-equivalent scores may represent less restraint in obese individuals than in normal-weight people. The psychometric evaluation of the Restraint Scale also revealed that the scale was less reliable in the obese than in the normal-weight population and seemed to tap somewhat different constructs in the two subpopulations. Factor analyses yielded a two-dimensional solution in the normal-weight group and a four-dimensional solution in the obese group. Correlations of the scale with a measure of Defensiveness also differed in the two samples. These results indicate that the norms, reliability and construct validity of the scale differ for obese and normal-weight populations. If restraint theory’s predictions concerning the relations between restraint and obesity are to be adequately tested these differences must be taken into account.
INTRODUCTION
Research concerning Herman’s theory of restrained eating (Herman, 1978) has relied heavily on the Restraint Questionnaire (Herman, Polivy, Pliner, Threlkeld and Munic, 1978). Although this questionnaire, or an earlier version of it (Herman and Mack, 1975), has been used in all studies of restraint theory, there is little published information concerning its psychometric properties. The scale’s ability to predict behavior in experimental settings (Herman and Mack, 1975; Herman and Polivy, 1975; Herman et al., 1978; Hibscher and Herman, 1977; Polivy, 1976; Polivy, Herman and Warsh, 1978) provides some evidence for its predictive and construct validity. However, this supportive evidence is limited since it is all found in studies which used samples comprised primarily of normal-weight individuals. Restraint theory is intended to explain the behavior of obese individuals and tests of the theory in overweight samples have not supported all of its predictions (Ruderman and Wilson, 1979; Ruderman and Christensen, 1983). These findings in overweight groups may reflect a need for modification of the theory, and/or differences in the measurement characteristics of the Restraint Scale in overweight and normal-weight populations. Restraint theory explains why the eating patterns of obese individuals differ from those of normal-weight people. Two basic hypotheses comprise the theory. The first is that dietary self-control (Restraint) is a major determinant of eating patterns. The second hypothesis is that the eating patterns of obese individuals are due entirely to the high level of restraint found in the obese population. The eating pattern most frequently studied in investigations of restraint theory is binge eating. In support of the hypothesis that Restraint scores can predict eating patterns, research has shown that unrestrained eaters (non-dieters) consume less after a preload than without one, while restrained eaters (dieters) do the reverse (Herman and Mack, 1975; Hibscher and Herman, 1977). The pattern demonstrated by unrestrained eaters has been called ‘regulatory’ eating while that demonstrated by restrained eaters has been termed ‘counter-regulatory’ eating. While the hypothesis that Restraint scores can predict behavior has been supported, the hypothesis that the eating patterns of obese individuals are due to the high level of restraint found among them has not been corroborated. Comparisons between obese and normal-weight individuals blocked on Restraint scores revealed that the obese individuals ate significantly less after a preload than without one, while normal-weight people ate similar amounts with and without the 253
254
AUDREY J. RUDERMAN
preload (Ruderman and Wilson, 1979; Ruderman and Christensen, 1983). Ruderman and Christensen (1983) also found that Restraint scores predicted different behavior in obese and normal-weight groups. Among obese individuals unrestrained eaters ate more than restrained eaters, while among normal-weight people, the reverse was true. It is difficult to determine whether these results reflect di~culties in restraint theory and/or the Restraint Scale. An examination of the face validity of the items on the questionnaire suggests that the scale may at least in part be responsible for these findings. Four of the ten items on the scale concern weight fluctuations measured in pounds with larger fluctuations earning more points. Because of this the scores of obese individuals may be inflated. Numerically-equivalent Restraint scores may represent a lower degree of restraint in obese individuals than they do in normal-weight subjects. This could explain the consistent finding in studies blocking weight groups on Restraint scores that obese individuals demonstrate a greater reduction in intake following a preload than do nodal-weight people. In such studies the obese subjects selected would be systematically less restrained than the normal-weight group. Examination of the questionnaire items also suggests that the scale may tap somewhat different constructs in obese and normal-weight groups. The four items mentioned above dealing with size of weight fluctuations seem likely to be tapping different constructs in individuals at their ideal weight and in individuals currently overweight. In the former it may be indicative of an unstable weight history associated with dieting, while in the latter it may reflect current degree of overweight. Social Desirability factors might also effect the two groups differently. Endorsement of questions concerning being on a diet seems a more socially-desirable behavior for obese people than for individuals of normal weight. Considerations such as this suggest that the Restraint Scale may tap somewhat different dimensions in obese and normal-weight people. The purpose of the present studies was to examine the psychometric properties of the Restraint Scale separately in obese and normal-weight samples in order to determine if the scale can be applied to both groups in the same way.
STUDY
1
The purpose of this study was to examine and compare the internal properties of the Restraint Scale in obese and normal-weight samples. Method Subjects and procedures
Subjects were 167 female undergraduates enrolled in Introductory Psychology at the University of Illinois at Chicago Circle. The Restraint Questionnaire was administered to groups ranging from 15 to 25 individuals. After completing the questionnaire each S’s height and weight were measured individually. Individuals were categorized as obese or normal weight by the extent to which their weight deviated from their ideal weight based on the Metropolitan Life Insurance Company norms for desirable weights for women. Individuals 15% or more above their ideal weight were categorized as overweight. Those between 20”/”below ideal weight and 10% above were categorized as normal weight. The obese group consisted of 58 individuals and had a mean of 3404 overweight. The normal-weight group consisted of 89 individuals and had a mean of 0.10% below ideal weight. Results Norms
In the normal-weight sample, the mean Restraint score was 14.93, the median score was 16 and the SD was 6.67. Scores ranged from 0 to 26. In the obese sample the mean Restraint score was 18.74, the median was 19 and the SD was 3.95. Scores ranged from 9 to 29. An F-test comparing the variability in the two groups revealed that the Restraint scores of the normal-weight group were significantIy more heterogeneous than those of the obese group, F(88, 57) = 2.85, P < 0.001. A t-test for populations with unequal variances revealed that the mean Restraint score was significantly higher in the obese than in the normal-weight group, t = 4.34, P < 0.001.
The Restraint Table
I. Item-analvsis
summary
Scale
255
for the Restraint
Questionnaire Correlation*
1. How often are you dieting? 2. What is the maximum amount of weight (in pounds) you have ever lost within 1 month? 3. What is your maximum weight gain within a week? 4. In a typical week, how much does your weight fluctuate? of 5. Would a weight fluctuation 5 lb affect the way you live your life? 6. Do you eat sensibly in front of others and splurge alone? 7. Do you give too much time and thought to food? 8. Do you have feelings of guilt after overeating? 9. How conscious are you of what you’re eating? 10. How many pounds over your desired weight were you at your maximum weight?
Normal
Obese
0.69
0.35
0.51
0.37
0.60
0.36
0.52
0.53
0.53
-0.21
0.39
0.17
0.56
0.17
0.68
0.28
0.54
- 0.02
0.65
0.20
*Correlation of an item with the total-scale score where the variance the particular item has been removed from the total score.
of
Reliability The reliability of the scale was assessed using coefficient alpha, a measure of internal consistency. Alpha was 0.86 in the normal-weight sample and 0.51 in the obese sample. The item/total-scale correlations on which coefficient alpha is based are listed separately for each sample in Table 1. The reliability coefficients reveal that 14% of the variance in the normal-weight sample was due to error variance, while 49% of the variance in the obese group was attributable to error variance. The index of reliability (the square root of the reliability coefficient) was significantly higher in the normal-weight than in the obese group, z2 = 55.65, P < 0.0001 (Fisher’s Z-transformation test for two Pearson r’s). Construct validity The construct validity of a test is the extent to which it measures the theoretical construct it is intended to assess (Anastasi, 1982). As one method of examining this, the dimensionality of the Restraint Scale was examined using a principal-components factor analysis. Factors with eigenvalues greater than one were retained and rotated orthogonally (Varimax). Separate analyses were done for the obese and normal-weight groups. In the normal-weight sample a two-dimensional solution emerged. The first factor reflected a Concern with Dieting dimension and the second a Weight Fluctuation dimension. Table 2 shows factor loadings over 0.5 for the two rotated factors. The first factor accounted for 32% of the variance and the second for 27%. In the obese sample a four-dimensional solution emerged. The first factor reflected a Weight Fluctuation dimension, the second a Bingeing dimension, the third a Tendency to Diet dimension and the fourth an Overconcern with Dieting. Table 2 has factor loadings over 0.5 for the four rotated factors. The first factor accounted for 25% of the variance, the second for 17”/,, the third for 15% and the fourth for 12%. The results of the factor analyses indicate that the Restraint items dealing with changes in body weight tap a Weight Fluctuation dimension in both obese and normal-weight populations. However, the remaining items seem to tap a single construct in the normal-weight sample, and several distinct dimensions in the obese group. In addition to the results of factor analysis, the Restraint Scale’s relations with other variables provide information regarding the scale’s construct
AUDREY J. RUUERMAN
256 Table 2. Factor
structure
Item
1 2 3 4 5 6 I 8 9 10
of the Restraint Scale items in obese and normal-weight groups Obese
Normals Concern Weight Weight Weight Concern Concern Concern Concern Concern Weight
Tendency to Diet Weight Fluctuation Weight Fluctuation Weight Fluctuation Weight Fluctuation Bingeing (F2) Overconcern with Bingeing (F2) Tendency to Diet Weight Fluctuation Overconcern with
with Dieting (Fl) Fluctuation (F2) Fluctuation (F2) Fluctuation (F2) with Dieting (Fl) with Dieting (Fl) with Dieting (FJ) with Dieting (Fl) with Dieting (Fl) Fluctuation (F2)
(F3) (Fl) (Fl) (Fl) (F I) Dieting
(F4)
(F3) (Fl) Dieting
(F4)
validity. According to restraint theory, Restraint is a dimension distinct from degree of overweight, but correlated with it. Percent of ideal weight (weight/ideal weight) and Restraint scores were moderately and significantly related, r = 0.37, P < 0.001.
STUDY
2
The purpose of this study was to further examine the construct validity of the Restraint Scale. The relations between Restraint and Social Desirability and Defensiveness were investigated. It was hypothesized that endorsement of items concerning dieting and weight loss might tap a need to appear in a socially-acceptable light in the obese group, but not in the normal-weight group. Method Subjects and procedures
This study involved 295 Ss enrolled in Introductory Psychology at the University of Illinois at Chicago Circle. In order to become eligible for several studies conducted by the Psychology Department, Ss completed a battery of questionnaires. Included among these were the Restraint Scale and two measures of a need to appear in a socially-acceptable light, the Marlowe-Crowne Social Desirability Scale (Crowne and Marlowe, 1964) and the Lie Scale of the Eysenck Personality Inventory (Eysenck and Eysenck, 1963). Both measures were included since they tap different aspects of concern with social acceptability. The Marlowe-Crowne measures an overt need to deny faults and appear moral and conscientious, while the Eysenck Lie Scale measures defensiveness and guardedness, more subtle reflections of the need to appear in a favorable light. Ss also reported their height and weight. The actual heights and weights of 96 of these individuals were recorded later during their participation in another experiment. Subjects were categorized as obese or normal weight by the extent to which their self-reported weight differed from their ideal weight based on the Metropolitan Life Insurance Company norms for desirable weights for women. The data from the 96 individuals who were weighed and measured were used to estimate the extent to which self-reported weight was accurate. The mean self-reported weight was 304 less than actual weight. Among obese individuals self-reported weight was 6% less than actual weight and among normal-weight individuals self-reported weight averaged 1.5% less than actual weight. Taking this tendency to underestimate weight into account, fs who by their self-report were less than 7% overweight were categorized as normal weight. Those who by their self-report were 15% or more above ideal weight were categorized as obese. The obese group consisted of 69 individuals and had a mean reported weight of 29% overweight. The normal-weight group consisted of 176 individuals and had a mean reported weight of 404 below ideal weight.
If the Restraint Scale is measuring the same construct in obese and normal-weight groups, correlations between Restraint and the other measures in this study, the Marlowe-Crowne Social Desirability Scale and the Eysenck Lie Scale should be similar in both groups, Using Fisher’s
The Restraint
Scale
251
Z-transformation (Darlington, 1975) for testing the hypothesis that two Pearson r’s are equal, the two pairs of correlations were compared. The relation between Defensiveness (Eysenck Lie Scale) and Restraint was significantly stronger in the normal-weight sample than in the obese group, z2 = 47.7, P < 0.001. In the normal-weight group, there was a strong tendency for Defensiveness to decrease as Restraint scores increased, r = -0.70, while in the obese group there was little relation between these measures, r = 0.13. Relations between the Marlowe-Crowne Social Desirability Scale and Restraint did not differ in the two samples. In the obese group, r = - 0.15, and in the normal-weight group r = -0.20. DISCUSSION
Research investigating restraint theory has supported the hypothesis that Restraint scores predict eating behavior. However, restraint theory’s hypothesis that the eating habits of obese individuals are similar to those of restrained eaters has not been corroborated. Contrary to restraint theory’s predictions, obese subjects have demonstrated eating patterns similar to those of unrestrained eaters (Ruderman and Wilson, 1979; Ruderman and Christensen, 1983). This finding may reflect problems in restraint theory/and or the Restraint Scale. As a first step toward investigating these possibilities the present study examined the psychometric characteristics of the Restraint Scale for obese and normal-weight samples separately. The results indicated that different norms apply to the two populations. Restraint scores were significantly higher and more homogenous in the obese sample than in the normal-weight group. This suggests that obese and normal-weight people use the Restraint Scale differently with obese individuals choosing responses toward the high end of the scale. To establish unequivocally that the difference found here represents differences in the use of the scale, rather than true differences in the level of restraint in obese and normal-weight people would require validating Restraint scores against some external criterion. The present study did not include such a measure. However, past studies have measured food consumption and its relation to restraint in obese and normal-weight samples. Restraint theory predicts that Restraint moderates food consumption following a preload. Restrained eaters are expected to eat more after a preload than without one, while unrestrained eaters are expected to do the opposite. Research has demonstrated the following pattern: restrained normal-weight people eat somewhat more after preload than without one, restrained obese individuals eat similar amounts with and without a preload, unrestrained normal-weight people eat somewhat less after a preload than without one, and unrestrained obese people eat considerably less after a preload than without one (Ruderman and Wilson, 1979; Ruderman and Christensen, 1983). This pattern in conjunction with the normative data collected here strongly suggests that numerically-equivalent Restraint scores represent less restraint in obese than in normal-weight groups. In addition to having higher norms in the obese than in the normal-weight sample, the Restraint Scale also had a lower level of internal consistency (reliability) in the obese group. This finding was consistent with the factor analyses which indicated that the data from the normal-weight group fit a two-dimensional solution. while the data from the obese group fit a four-dimensional solution. These results suggest that some of the scale items have different meanings in the two subpopulations and that the scale taps somewhat different constructs in the two groups. For the normal-weight sample, the scale seems to meet reasonable psychometric standards and is interpretable as a measure of concern with dieting and history of weight instability. The scale’s meaning in the obese sample is less clear and its reliability less acceptable. The relations between Restraint scores and external variables also suggest that the scale is tapping somewhat different constructs in obese and normal-weight samples. The finding that Defensiveness (Eysenck Lie Scale) was highly and negatively related to Restraint scores in the normal-weight, but not the obese sample suggests that endorsement of the restraint items was perceived negatively by the normal-weight people, but not by the obese individuals. This is consistent with the finding that Restraint scores were significantly higher in the obese than in the normal-weight group. Caution is necessary in applying the Restraint Scale to obese populations. It appears that the scale’s norms, reliability and validity are different in obese groups than they are in normal-weight samples. These data do not fully resolve the issue of whether the negative
AUDREYJ. RUDERMAN
258
findings of past studies testing the predictions of restraint theory in obese samples are due to problems in the scale, or to the theory. However, they indicate that if the theory is to have a fair test, the differences in the psychometric properties of the scale in obese and normal-weight populations need to be addressed. REFERENCES Anastasi A. (1982) Crowne
Psychological
D. P. and Marlowe
Testing. Macmillan, New York. D. (1960) A new scale of social desirability
independent
of psychopathology.
J. consult. Psychol.
24, 349-354.
Darlington R. B. (1975) Radicals and Squares. Logan Hill Press, Ithaca. New York. Eysenck H. J. and Eysenck S. B. G. (1963) Eysenck Personality Inventory. Educational & Industrial Testing Service, San Diego, California. Herman C. P. and Mack D. (1975) Restrained and unrestrained eating. J. Person. 43, 657-660. Herman C. P. and Polivy J. (1975) Anxiety, restraint and eating behavior. J. ahnorm. Psychol. 84, 666-672. Herman C. P., Polivy J., Pliner P., Threlkeld J. and Munic D. (1978) Distractibility in dieters and non-dieters: an alternative view of “externality”. J. Person. sot. Psychol. 36, 536548. Hibscher A. and Herman C. P. (1977) Obesity, dieting and the expression of “obese” characteristics, J. camp. physiol. Psychol.
91, 374-380.
Polivy J. (1976) Perception of calories and regulation of intake in restrained and unrestrained subjects. Addict. Eehao. 1, 2377243. Polivy I., Herman C. P. and Warsh S. (1978) Internal and external components of emotionality in restrained and unrestrained subjects. J. ahnorm. Psychoi. 87, 497-504. Ruderman A. J. and Christensen H. (1983) Restraint theory and its applicability to overweight individuals. J. abnorm. Psycho/ In press. Ruderman A. J. and Wilson G. T. (1979) Weight, restraint, cognitions and counterregulation. Behao. Res. Thu. 17, 581~590.
THE
1983
OOOS-7967/83/030253-06$03.00/O Pergamon Press Ltd
RESTRAINT SCALE: A PSYCHOMETRIC INVESTIGATION AUDREY
University
of Illinois at Chicago
Circle, Department
J.
RUDERMAN of Psychology,
(Receioed 21 September
Box 4348, Chicago,
IL 60680, U.S.A.
1982)
Summary-The psychometric characteristics of the Restraint Scale in obese and normal-weight subjects were compared. Scores were significantly higher and more homogeneous in the obese than in the normal-weight group. In light of previous studies indicating that obese subjects behave like normal-weight subjects whose Restraint scores are several points (approx. 3-6) lower, the present result was interpreted as suggesting that numerically-equivalent scores may represent less restraint in obese individuals than in normal-weight people. The psychometric evaluation of the Restraint Scale also revealed that the scale was less reliable in the obese than in the normal-weight population and seemed to tap somewhat different constructs in the two subpopulations. Factor analyses yielded a two-dimensional solution in the normal-weight group and a four-dimensional solution in the obese group. Correlations of the scale with a measure of Defensiveness also differed in the two samples. These results indicate that the norms, reliability and construct validity of the scale differ for obese and normal-weight populations. If restraint theory’s predictions concerning the relations between restraint and obesity are to be adequately tested these differences must be taken into account.
INTRODUCTION
Research concerning Herman’s theory of restrained eating (Herman, 1978) has relied heavily on the Restraint Questionnaire (Herman, Polivy, Pliner, Threlkeld and Munic, 1978). Although this questionnaire, or an earlier version of it (Herman and Mack, 1975), has been used in all studies of restraint theory, there is little published information concerning its psychometric properties. The scale’s ability to predict behavior in experimental settings (Herman and Mack, 1975; Herman and Polivy, 1975; Herman et al., 1978; Hibscher and Herman, 1977; Polivy, 1976; Polivy, Herman and Warsh, 1978) provides some evidence for its predictive and construct validity. However, this supportive evidence is limited since it is all found in studies which used samples comprised primarily of normal-weight individuals. Restraint theory is intended to explain the behavior of obese individuals and tests of the theory in overweight samples have not supported all of its predictions (Ruderman and Wilson, 1979; Ruderman and Christensen, 1983). These findings in overweight groups may reflect a need for modification of the theory, and/or differences in the measurement characteristics of the Restraint Scale in overweight and normal-weight populations. Restraint theory explains why the eating patterns of obese individuals differ from those of normal-weight people. Two basic hypotheses comprise the theory. The first is that dietary self-control (Restraint) is a major determinant of eating patterns. The second hypothesis is that the eating patterns of obese individuals are due entirely to the high level of restraint found in the obese population. The eating pattern most frequently studied in investigations of restraint theory is binge eating. In support of the hypothesis that Restraint scores can predict eating patterns, research has shown that unrestrained eaters (non-dieters) consume less after a preload than without one, while restrained eaters (dieters) do the reverse (Herman and Mack, 1975; Hibscher and Herman, 1977). The pattern demonstrated by unrestrained eaters has been called ‘regulatory’ eating while that demonstrated by restrained eaters has been termed ‘counter-regulatory’ eating. While the hypothesis that Restraint scores can predict behavior has been supported, the hypothesis that the eating patterns of obese individuals are due to the high level of restraint found among them has not been corroborated. Comparisons between obese and normal-weight individuals blocked on Restraint scores revealed that the obese individuals ate significantly less after a preload than without one, while normal-weight people ate similar amounts with and without the 253
254
AUDREY J. RUDERMAN
preload (Ruderman and Wilson, 1979; Ruderman and Christensen, 1983). Ruderman and Christensen (1983) also found that Restraint scores predicted different behavior in obese and normal-weight groups. Among obese individuals unrestrained eaters ate more than restrained eaters, while among normal-weight people, the reverse was true. It is difficult to determine whether these results reflect di~culties in restraint theory and/or the Restraint Scale. An examination of the face validity of the items on the questionnaire suggests that the scale may at least in part be responsible for these findings. Four of the ten items on the scale concern weight fluctuations measured in pounds with larger fluctuations earning more points. Because of this the scores of obese individuals may be inflated. Numerically-equivalent Restraint scores may represent a lower degree of restraint in obese individuals than they do in normal-weight subjects. This could explain the consistent finding in studies blocking weight groups on Restraint scores that obese individuals demonstrate a greater reduction in intake following a preload than do nodal-weight people. In such studies the obese subjects selected would be systematically less restrained than the normal-weight group. Examination of the questionnaire items also suggests that the scale may tap somewhat different constructs in obese and normal-weight groups. The four items mentioned above dealing with size of weight fluctuations seem likely to be tapping different constructs in individuals at their ideal weight and in individuals currently overweight. In the former it may be indicative of an unstable weight history associated with dieting, while in the latter it may reflect current degree of overweight. Social Desirability factors might also effect the two groups differently. Endorsement of questions concerning being on a diet seems a more socially-desirable behavior for obese people than for individuals of normal weight. Considerations such as this suggest that the Restraint Scale may tap somewhat different dimensions in obese and normal-weight people. The purpose of the present studies was to examine the psychometric properties of the Restraint Scale separately in obese and normal-weight samples in order to determine if the scale can be applied to both groups in the same way.
STUDY
1
The purpose of this study was to examine and compare the internal properties of the Restraint Scale in obese and normal-weight samples. Method Subjects and procedures
Subjects were 167 female undergraduates enrolled in Introductory Psychology at the University of Illinois at Chicago Circle. The Restraint Questionnaire was administered to groups ranging from 15 to 25 individuals. After completing the questionnaire each S’s height and weight were measured individually. Individuals were categorized as obese or normal weight by the extent to which their weight deviated from their ideal weight based on the Metropolitan Life Insurance Company norms for desirable weights for women. Individuals 15% or more above their ideal weight were categorized as overweight. Those between 20”/”below ideal weight and 10% above were categorized as normal weight. The obese group consisted of 58 individuals and had a mean of 3404 overweight. The normal-weight group consisted of 89 individuals and had a mean of 0.10% below ideal weight. Results Norms
In the normal-weight sample, the mean Restraint score was 14.93, the median score was 16 and the SD was 6.67. Scores ranged from 0 to 26. In the obese sample the mean Restraint score was 18.74, the median was 19 and the SD was 3.95. Scores ranged from 9 to 29. An F-test comparing the variability in the two groups revealed that the Restraint scores of the normal-weight group were significantIy more heterogeneous than those of the obese group, F(88, 57) = 2.85, P < 0.001. A t-test for populations with unequal variances revealed that the mean Restraint score was significantly higher in the obese than in the normal-weight group, t = 4.34, P < 0.001.
The Restraint Table
I. Item-analvsis
summary
Scale
255
for the Restraint
Questionnaire Correlation*
1. How often are you dieting? 2. What is the maximum amount of weight (in pounds) you have ever lost within 1 month? 3. What is your maximum weight gain within a week? 4. In a typical week, how much does your weight fluctuate? of 5. Would a weight fluctuation 5 lb affect the way you live your life? 6. Do you eat sensibly in front of others and splurge alone? 7. Do you give too much time and thought to food? 8. Do you have feelings of guilt after overeating? 9. How conscious are you of what you’re eating? 10. How many pounds over your desired weight were you at your maximum weight?
Normal
Obese
0.69
0.35
0.51
0.37
0.60
0.36
0.52
0.53
0.53
-0.21
0.39
0.17
0.56
0.17
0.68
0.28
0.54
- 0.02
0.65
0.20
*Correlation of an item with the total-scale score where the variance the particular item has been removed from the total score.
of
Reliability The reliability of the scale was assessed using coefficient alpha, a measure of internal consistency. Alpha was 0.86 in the normal-weight sample and 0.51 in the obese sample. The item/total-scale correlations on which coefficient alpha is based are listed separately for each sample in Table 1. The reliability coefficients reveal that 14% of the variance in the normal-weight sample was due to error variance, while 49% of the variance in the obese group was attributable to error variance. The index of reliability (the square root of the reliability coefficient) was significantly higher in the normal-weight than in the obese group, z2 = 55.65, P < 0.0001 (Fisher’s Z-transformation test for two Pearson r’s). Construct validity The construct validity of a test is the extent to which it measures the theoretical construct it is intended to assess (Anastasi, 1982). As one method of examining this, the dimensionality of the Restraint Scale was examined using a principal-components factor analysis. Factors with eigenvalues greater than one were retained and rotated orthogonally (Varimax). Separate analyses were done for the obese and normal-weight groups. In the normal-weight sample a two-dimensional solution emerged. The first factor reflected a Concern with Dieting dimension and the second a Weight Fluctuation dimension. Table 2 shows factor loadings over 0.5 for the two rotated factors. The first factor accounted for 32% of the variance and the second for 27%. In the obese sample a four-dimensional solution emerged. The first factor reflected a Weight Fluctuation dimension, the second a Bingeing dimension, the third a Tendency to Diet dimension and the fourth an Overconcern with Dieting. Table 2 has factor loadings over 0.5 for the four rotated factors. The first factor accounted for 25% of the variance, the second for 17”/,, the third for 15% and the fourth for 12%. The results of the factor analyses indicate that the Restraint items dealing with changes in body weight tap a Weight Fluctuation dimension in both obese and normal-weight populations. However, the remaining items seem to tap a single construct in the normal-weight sample, and several distinct dimensions in the obese group. In addition to the results of factor analysis, the Restraint Scale’s relations with other variables provide information regarding the scale’s construct
AUDREY J. RUUERMAN
256 Table 2. Factor
structure
Item
1 2 3 4 5 6 I 8 9 10
of the Restraint Scale items in obese and normal-weight groups Obese
Normals Concern Weight Weight Weight Concern Concern Concern Concern Concern Weight
Tendency to Diet Weight Fluctuation Weight Fluctuation Weight Fluctuation Weight Fluctuation Bingeing (F2) Overconcern with Bingeing (F2) Tendency to Diet Weight Fluctuation Overconcern with
with Dieting (Fl) Fluctuation (F2) Fluctuation (F2) Fluctuation (F2) with Dieting (Fl) with Dieting (Fl) with Dieting (FJ) with Dieting (Fl) with Dieting (Fl) Fluctuation (F2)
(F3) (Fl) (Fl) (Fl) (F I) Dieting
(F4)
(F3) (Fl) Dieting
(F4)
validity. According to restraint theory, Restraint is a dimension distinct from degree of overweight, but correlated with it. Percent of ideal weight (weight/ideal weight) and Restraint scores were moderately and significantly related, r = 0.37, P < 0.001.
STUDY
2
The purpose of this study was to further examine the construct validity of the Restraint Scale. The relations between Restraint and Social Desirability and Defensiveness were investigated. It was hypothesized that endorsement of items concerning dieting and weight loss might tap a need to appear in a socially-acceptable light in the obese group, but not in the normal-weight group. Method Subjects and procedures
This study involved 295 Ss enrolled in Introductory Psychology at the University of Illinois at Chicago Circle. In order to become eligible for several studies conducted by the Psychology Department, Ss completed a battery of questionnaires. Included among these were the Restraint Scale and two measures of a need to appear in a socially-acceptable light, the Marlowe-Crowne Social Desirability Scale (Crowne and Marlowe, 1964) and the Lie Scale of the Eysenck Personality Inventory (Eysenck and Eysenck, 1963). Both measures were included since they tap different aspects of concern with social acceptability. The Marlowe-Crowne measures an overt need to deny faults and appear moral and conscientious, while the Eysenck Lie Scale measures defensiveness and guardedness, more subtle reflections of the need to appear in a favorable light. Ss also reported their height and weight. The actual heights and weights of 96 of these individuals were recorded later during their participation in another experiment. Subjects were categorized as obese or normal weight by the extent to which their self-reported weight differed from their ideal weight based on the Metropolitan Life Insurance Company norms for desirable weights for women. The data from the 96 individuals who were weighed and measured were used to estimate the extent to which self-reported weight was accurate. The mean self-reported weight was 304 less than actual weight. Among obese individuals self-reported weight was 6% less than actual weight and among normal-weight individuals self-reported weight averaged 1.5% less than actual weight. Taking this tendency to underestimate weight into account, fs who by their self-report were less than 7% overweight were categorized as normal weight. Those who by their self-report were 15% or more above ideal weight were categorized as obese. The obese group consisted of 69 individuals and had a mean reported weight of 29% overweight. The normal-weight group consisted of 176 individuals and had a mean reported weight of 404 below ideal weight.
If the Restraint Scale is measuring the same construct in obese and normal-weight groups, correlations between Restraint and the other measures in this study, the Marlowe-Crowne Social Desirability Scale and the Eysenck Lie Scale should be similar in both groups, Using Fisher’s
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Z-transformation (Darlington, 1975) for testing the hypothesis that two Pearson r’s are equal, the two pairs of correlations were compared. The relation between Defensiveness (Eysenck Lie Scale) and Restraint was significantly stronger in the normal-weight sample than in the obese group, z2 = 47.7, P < 0.001. In the normal-weight group, there was a strong tendency for Defensiveness to decrease as Restraint scores increased, r = -0.70, while in the obese group there was little relation between these measures, r = 0.13. Relations between the Marlowe-Crowne Social Desirability Scale and Restraint did not differ in the two samples. In the obese group, r = - 0.15, and in the normal-weight group r = -0.20. DISCUSSION
Research investigating restraint theory has supported the hypothesis that Restraint scores predict eating behavior. However, restraint theory’s hypothesis that the eating habits of obese individuals are similar to those of restrained eaters has not been corroborated. Contrary to restraint theory’s predictions, obese subjects have demonstrated eating patterns similar to those of unrestrained eaters (Ruderman and Wilson, 1979; Ruderman and Christensen, 1983). This finding may reflect problems in restraint theory/and or the Restraint Scale. As a first step toward investigating these possibilities the present study examined the psychometric characteristics of the Restraint Scale for obese and normal-weight samples separately. The results indicated that different norms apply to the two populations. Restraint scores were significantly higher and more homogenous in the obese sample than in the normal-weight group. This suggests that obese and normal-weight people use the Restraint Scale differently with obese individuals choosing responses toward the high end of the scale. To establish unequivocally that the difference found here represents differences in the use of the scale, rather than true differences in the level of restraint in obese and normal-weight people would require validating Restraint scores against some external criterion. The present study did not include such a measure. However, past studies have measured food consumption and its relation to restraint in obese and normal-weight samples. Restraint theory predicts that Restraint moderates food consumption following a preload. Restrained eaters are expected to eat more after a preload than without one, while unrestrained eaters are expected to do the opposite. Research has demonstrated the following pattern: restrained normal-weight people eat somewhat more after preload than without one, restrained obese individuals eat similar amounts with and without a preload, unrestrained normal-weight people eat somewhat less after a preload than without one, and unrestrained obese people eat considerably less after a preload than without one (Ruderman and Wilson, 1979; Ruderman and Christensen, 1983). This pattern in conjunction with the normative data collected here strongly suggests that numerically-equivalent Restraint scores represent less restraint in obese than in normal-weight groups. In addition to having higher norms in the obese than in the normal-weight sample, the Restraint Scale also had a lower level of internal consistency (reliability) in the obese group. This finding was consistent with the factor analyses which indicated that the data from the normal-weight group fit a two-dimensional solution. while the data from the obese group fit a four-dimensional solution. These results suggest that some of the scale items have different meanings in the two subpopulations and that the scale taps somewhat different constructs in the two groups. For the normal-weight sample, the scale seems to meet reasonable psychometric standards and is interpretable as a measure of concern with dieting and history of weight instability. The scale’s meaning in the obese sample is less clear and its reliability less acceptable. The relations between Restraint scores and external variables also suggest that the scale is tapping somewhat different constructs in obese and normal-weight samples. The finding that Defensiveness (Eysenck Lie Scale) was highly and negatively related to Restraint scores in the normal-weight, but not the obese sample suggests that endorsement of the restraint items was perceived negatively by the normal-weight people, but not by the obese individuals. This is consistent with the finding that Restraint scores were significantly higher in the obese than in the normal-weight group. Caution is necessary in applying the Restraint Scale to obese populations. It appears that the scale’s norms, reliability and validity are different in obese groups than they are in normal-weight samples. These data do not fully resolve the issue of whether the negative
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findings of past studies testing the predictions of restraint theory in obese samples are due to problems in the scale, or to the theory. However, they indicate that if the theory is to have a fair test, the differences in the psychometric properties of the scale in obese and normal-weight populations need to be addressed. REFERENCES Anastasi A. (1982) Crowne
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Darlington R. B. (1975) Radicals and Squares. Logan Hill Press, Ithaca. New York. Eysenck H. J. and Eysenck S. B. G. (1963) Eysenck Personality Inventory. Educational & Industrial Testing Service, San Diego, California. Herman C. P. and Mack D. (1975) Restrained and unrestrained eating. J. Person. 43, 657-660. Herman C. P. and Polivy J. (1975) Anxiety, restraint and eating behavior. J. ahnorm. Psychol. 84, 666-672. Herman C. P., Polivy J., Pliner P., Threlkeld J. and Munic D. (1978) Distractibility in dieters and non-dieters: an alternative view of “externality”. J. Person. sot. Psychol. 36, 536548. Hibscher A. and Herman C. P. (1977) Obesity, dieting and the expression of “obese” characteristics, J. camp. physiol. Psychol.
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Polivy J. (1976) Perception of calories and regulation of intake in restrained and unrestrained subjects. Addict. Eehao. 1, 2377243. Polivy I., Herman C. P. and Warsh S. (1978) Internal and external components of emotionality in restrained and unrestrained subjects. J. ahnorm. Psychoi. 87, 497-504. Ruderman A. J. and Christensen H. (1983) Restraint theory and its applicability to overweight individuals. J. abnorm. Psycho/ In press. Ruderman A. J. and Wilson G. T. (1979) Weight, restraint, cognitions and counterregulation. Behao. Res. Thu. 17, 581~590.