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Covert sensitization and information in the reduction of nailbiting
B E H A V I O R T H E R A P Y 7 , 512--518
(1976)
Covert Sensitization and Information in the Reduction of Nailbiting A N N A - M A R I E DAVIDSON AND DOUGLAS R . D E N N E Y
University of Kansas The relative effectiveness of covert sensitization and information in bringing about a reduction in nailbiting was investigated. The information procedure was devised as an attention-placebo treatment which was equated with covert sensitization in terms of nonspecific treatment factors such as demand, expectancy, and the degree to which attention was focused upon ones nails. Three treatment groups, covert sensitization, information, and combined treatment, were compared with a waiting-list control group in a 2 (Covert Sensitization) x 2 (Information) design. The dependent variable was the length of subjects' nails measured at a pre-test, post-test, and 5-week follow-up test. Contrary to prediction, covert sensitization did not emerge as a significant treatment procedure, and information did. Nonspecific treatment factors appeared to be sufficient to bring about substantial increases in the length of subjects' nails, and there was no evidence that covert sensitization improved upon the contribution of these nonspecific factors.
Estimates of the prevalence of nailbiting among college students indicate nailbiting to be a behavioral problem of some magnitude, affecting about 27% of this population (e.g., Coleman & McCalley, 1948). Techniques reported to be successful in treating nailbiting include the use of bitter substances applied to the nails (BiUig, 1941; Blount, 1931), negative practice (Dunlap, 1932; Smith, 1957), hypnotic suggestion (Gruenewald, 1965), self-administered electric shocks (Bucher, 1968), self-monitoring and the substitution of incompatible responses (Azrin & Nunn, 1973; Horan, Hoffman, & Macri, 1974; McNamara, 1972), and response-cost procedures (Stephens & Koenig, 1970). Most of the above studies constitute little more than demonstrations of the application of each procedure to nailbiting. When adequate controls have been employed, results generally indicate that nonspecific treatment factors (e.g., expectancy and demand characteristics, attention to the nailbiting behavior, periodic examinations of subjects' nails) are sufficient to account for improvement. For example, Stephens and Koenig (1970) compared various response cost schedules in reducing nailbiting. Subjects in three groups had their monetary deposits returned according to three different schedules contingent upon not biting their nails. A fourth group Requests for reprints should be addressed to Douglas R. Denney, Department of Psychology, University of Kansas, Lawrence, KS 66045. 512 Copyright © 1976 by Association for Advancement of Behavior Therapy. All rights of reproduction in any form reserved.
COVERT SENSITIZATION AND NAILBITING
513
had their deposits returned contingent only upon appearing for each weekly appointment to have their nails measured. All four groups showed significant improvement from the pre- to the post-test, and although somewhat diminished, these improvements were still intact after a 3-month follow-up period. However, no significant difference was found between the four groups. In addition, McNamara (1972) studied four treatments procedures which combined self-monitoring and the substitution of incompatible responses (e.g., finger tapping). These four treatments were compared with a measurement-only group and a group explicitly told to continue biting their nails and to record this behavior. Significant increases in nail length occurred in all six groups, and again no significant difference was found between the groups. Covert sensitization has been successfully employed in reducing a wide variety of problem behaviors including "oral" habits such as smoking (Cautela, 1970), alcoholism (Ashem & Donner, 1968), and overeating (Janda & Rimm, 1972; Manno & Marston, 1972). Covert sensitization might also be an effective procedure for bringing about reductions in nailbiting beyond those attributable merely to nonspecific treatment factors. Thus, in the present study, covert sensitization therapy was compared with an informational therapy designed to equal the former in terms of the degree to which subjects were led to expect success and to focus attention upon their nails. The informational therapy did include general educational materials concerning nails (e.g., cosmetic care and composition of the nails, dietary hints, nail diseases) but the information was not specific to nailbiting. No mention of nailbiting and no direct attempt to impel subjects to stop biting their nails were included. To analyze the separate contributions made by the covert sensitization and information procedures within the study, a 2 (Covert Sensitization) × 2 (Information) design was employed in which covert sensitization, information, combined covert sensitization plus information, and waiting-list control groups were compared. The three treatment procedures were automated to standardize these procedures and to facilitate their group administration. A significant main effect for covert sensitization would indicate that this component had made an independent contribution to the effectiveness of the treatment. METHOD Subjects. Thirty-three subjects participated, with 19 females and 12 males completing the program. The subjects, ranging in age from 17 to 26 years (.Y = 19 years), were students enrolled in General Psychology who indicated that they had a problem with nailbiting. Participation satisfied a course-related research requirement. A pre-test questionnaire showed that, although 20% of the subjects had no recollection of when they had begun biting their nails, 74% estimated that they had begun before the age of 11. Forty-five percent claimed to engage in nailbiting more than 10 times a day, and all of them considered their nailbiting to
514
DAVIDSON AND DENNEY
be a serious problem which they were highly motivated to overcome. Seventy-seven percent had previously refrained from nailbiting long enough to notice an appreciable change in the conditions of their nails. Pre-testing. Each subject attended a group pre-test session during which his nails were measured to the nearest millimeter using a Verneer caliper. Nail length measurements were taken at the center of each nail, from the tip of the nail to base of the cuticle. The measurements were summed across all 10 of the subject's nails. Subjects also completed a preliminary questionnaire concerning previous nailbiting histories. Treatment. Subjects were randomly assigned to four groups: covert sensitization, information, combined treatment, and waiting-list control. Subjects in the first three groups were given eight treatment sessions, conducted twice weekly. During each treatment session, subjects were seated in semiprivate cubicles in a secluded room in the University language laboratory. Each subject wore headphones and listened to prerecorded treatments transmitted from a central control room. Covert sensitization. The covert sensitization tapes l a s t e d about 15 minutes, the first beginning with a brief rationale describing aversive conditioning. All eight tapes included brief relaxation exercises, followed by an aversive scene and an aversion-relief scene. 1 In the aversive scene, the subject was depicted as engaging in a series of responses leading up to and including nailbiting and then suffering graphically described aversive consequences such as nausea, vomitting, bleeding, and social disapproval. In the aversion-relief scene, the subject was depicted as starting to engage in nailbiting, beginning to feel nauseated, refraining from nailbiting and engaging in some incompatible behavior (e.g., breathing exercises, circulation exercises involving the hands), and feeling instantaneous relief and pride. Study-related situations were emphasized in several scenes, although a variety of additional problem situations conducive to nailbiting were also included. Generally, as the sessions progressed, the subject was depicted as becoming more adept at discriminating behaviors immediately preceding nailbiting and interrupting the chain at earlier points during the aversion-relief scenes. Information. The information tapes were also about 15 minutes in duration, the first beginning with a brief rationale suggesting that a change in attitude toward one's nails might reduce nailbiting. Topics covered on the eight tapes included (a) facts about nails, (b) the names of various parts of nails and cuticles, (c) nail care and manicure techniques, (d) prevention and repair of nail damage, (e) application of artificial nails, and (f) nail diseases. Combined treatment. Within each of eight sessions in this treatment, subjects received first the information and then the covert sensitization tape. Waiting list control. Subjects were told they would not receive treatment until later in the semester. Their nails were measured during the pre-test and the post-test sessions, but they received no intervening treatment. Following the post-test, the subjects were treated with the combined treatment procedure, and their nails were again measured during a 5-week followup session. Post-testing. All subjects' nails were again measured at a post-test session six weeks after the pre-test, and control subjects were scheduled for their forthcoming treatment sessions. Treated subjects completed a brief post-treatment questionnaire concerning their treatmentrelated behaviors during the course of therapy. A follow-up session was held five weeks after the post-test session. Nails were again measured. In addition, the control subjects, who had just completed their treatments, were asked to complete the post-treatment questionnaire. A transcript of one of the scenes employed in the covert sensitization therapy is available upon request.
COVERT SENSITIZATION AND NAILBITING
5 15
RESULTS Preliminary analyses indicated no significant difference between males and females in pre-test scores or changes from pre- to post-test. A 2(Covert Sensitization) × 2(Information) analysis of variance performed on the pre-test scores revealed no significant pre-test difference among the four groups. A 2(Covert Sensitization) × 2(Information) x 2(Trials) analysis of variance was then performed on the pre- and the post-test nail length measures. A significant main effect for Trials, F(1,27) = 32.80, p < .001, and a significant Information x Trials interaction, F(1,27) = 12.54, p < .005, were obtained. Although the pre-test measures did not differ significantly, a 2(Covert Sensitization) × 2(Information) analysis of covariance was performed on the post-test measures using the pre-test measures as covariate to correct for slight initial group differences. Information was the only significantly effective treatment component, F(1,27) = 12.71, p < .005. A one-way analysis of covariance applied to the post-test measures revealed a significant main effect for treatments, F(3,26) = 5.97,p < .005, which was analyzed further using Tukey B tests. Only the information group differed significantly (p < .05) from the waiting-list controls. A 3 (Treatments) × 2 (Trials) analysis of variance was performed on the nail length measures from the pre-test and the follow-up test sessions. The waiting-list Control subjects were excluded from this analysis since they had received treatment between the post-test and the follow-up test ses-
TABLE 1 MEANS AND STANDARD DEVISIONS OF NAIL LENGTH MEASURES (IN CENTIMETERS) Covert sensitization
Information
Combined treatment
Waiting-list controls
Preh test: x SD
10.25 1.65
10.01 1.78
9.27 2.17
9.02 1.97
Post test x SD
11.05 1.74
11.42 2.44
10.62 2.53
8.87 1.75
Follow-up test: x SD
11.27 1.87
11.49 2.28
11.08 3.03
10.79 2.11
Note. The treatment group Ns are 7 (covert sensitization), 8 (information), 7 (combined), and 9 (waiting-list control). Unweighted means were used in all the analyses.
516
DAVIDSON AND DENNEY
sions and therefore no longer represented an adequate baseline control group. This analysis revealed only a significant main effect for Trials, F (1, 19) = 32.07, p < .001. Subjects in the three treatment groups improved significantly from the pre-test to the follow-up test, and there was no differential effect among the three treatments. For the waiting-list control subjects, a significant decrease in nail length occurred between pre- and the post-test sessions, t (8) = 2.94, p < .02. However, a significant increase in nail length occurred from the post-test to the follow-up test, t (8) = 5.59, p < .001, and from the pre-test to the follow-up test, t (8) = 4.73, p < . 002. These increases are attributable to the combined treatment which control subjects received following the posttest session. Data from the preliminary questionnaire were analyzed in relation to changes in nail length measures over the course of treatment. Neither sex nor any of the variables extracted from the preliminary questionnaire (age at which nailbiting began, frequency with which nailbiting occurred each day, previous spontaneous attempts to stop nailbiting, perceived seriousness of ones nailbiting problem) were significantly related to improvement during treatment. DISCUSSION Contrary to prediction, covert sensitization did not contribute significantly to the improvement in nail length measures over the course of treatment. Furthermore, on the basis of specific comparisons between each treatment group and the control group, covert sensitization may have actually detracted from the effectiveness of information alone. The information group was the only group that differed significantly from controls at the time of the post-test. Comparisons among the three treatment groups revealed no significant difference at either post-test or follow-up, consistent with earlier studies (McNamara, 1972; Stephens & Koenig, 1970) and again indicating that nonspecific treatment factors alone may be principally responsible for improvements in subjects' nails. Clearly, covert sensitization did not enhance treatment effectiveness beyond that attributable to nonspecific treatment factors such as demand, expectancy, and attention to one's nails. The covert sensitization procedure was group administered and made use of standardized scenes. It might be argued that a more individualized procedure would have been more successful. However, although the relative efficacy of group vs. individual administrations of covert sensitization has not been studied, several investigators (e.g., Janda & Rimm, 1972; Manno & Marston, 1972) have reported successes using group administered covert sensitization. One might also argue that eight treatment sessions were too few for covert sensitization to emerge as a definitive treat-
COVERT SENSITIZATION AND NAILBITING
517
ment for nailbiting, although here again, other investigators focusing on other problems have reported successes using even fewer sessions (e.g., Janda & Rimm, 1972; Manno & Marston, 1972). The most cogent explanation for the present results is that nailbiting behaviors are so readily altered by nonspecific treatment factors that these factors alone are sufficient to bring about substantial changes in nail length. Within this context, covert sensitization could not be distinguished as an effective procedure. This explanation also has merit in terms of accounting for the lack of change in the waiting-list control group from the pre-test to the post-test. The untreated groups in the present study and in Smith's (1957) study did not improve between the pre-test and the post-test. However, both Stephens and Koenig (1970) and McNamara (1972) reported significant improvements for their untreated control groups. The difference seems to lie in how frequently subjects' nails were measured and whether the subjects believed themselves to be receiving treatment. In the latter two studies, subjects' nails were measured frequently and it seems quite obvious that subjects believed they were receiving treatment. In the present study, and presumably Smith's study, control subjects' nails were measured only twice and-subjects were explicitly told they were in a control group. The differences in nonspecific treatment factors such as attention, demand, and expectancy seem to account for the differences between these two types of untreated control groups. Once again, nonspecific treatment factors appear to be sufficient to bring about successful changes in subjects' nailbiting problem. The situation for nailbiting is not unlike that for smoking. Recent reviews (e.g., Hunt & Matarazzo, 1973; McFall & Hammen, 1971) indicate that almost any type of treatment is effective in bringing about substantial decreases in cigarette consumption from the pre- to the post-test. In the case of smoking, the problem becomes one of maintaining the initial treatment results over an extended follow-up period. Similarly, the present study, along with others, indicates that nailbiting is readily decreased from the pre- to the post-test by almost any treatment which focuses interest upon one's nails and contributes to subjects' expectancies for change. While these decreases were maintained intact during a five-week follow-up period, the question remains whether the nailbiting habit would reoccur over a more extended period, especially one in which subjects no longer expected their nails to be measured. REFERENCES Ashem, B., & Donner, L. Covert sensitization with alcoholics: A controlled replication. Behavior Research and Therapy, 1968, 6, 7-12.
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DAVIDSON AND DENNEY
Azrin, N. H., & Nunn. R. G. Habit reversal: A method of eliminating nervous habits and tics Behaviour Research and Theory, 1973, 11, 619-628. Billig, A. L. Finger nail-biting: Its incipiency, incidence, and amelioration. Genetic Psychological Monographs, 1941, 24, 123-218. Blount, R. E. Nail-biting is a real problem in high schools. Hygeia, t931, 9, 668-669. Bucher, B. D. A pocket-portable shock device with application to nailbiting. Behaviour Research and Therapy, 1968, 6, 389-392. Cautela, J. R. Treatment of smoking by covert sensitization. Psychological Reports, 1970, 26, 415--420. Coleman, J. C., & McCalley, J. E. Nailbiting among college students. Journal of Abnormal and Social Psychology, 1948, 43, 517-525. Dunlap, K. Habits: Their making and unmaking. N.Y.: Liveright, 1932. Gruenewald, D. Hypnotherapy in a case of adult nailbiting. The International Journal of Clinical and Experimental Hypnosis, 1965, 13, 209-219. Horan, J. J., Hoffman, A. M., & Macri, M. Self-control of chronic fingernail biting.Journal of Behavior Therapy and Experimental Psychiatry, 1974, 5, 307-309. Hunt, W. A., & Matarazzo, J. D. Three years later: Recent developments in the experimental modification of smoking behavior. Journal of Abnormal Psychology, 1973, 81, 107-114. Janda, L. H., & Rimm, D. C. Covert sensitization in the treatment of obesity. Journal of Abnormal Psychology, 1972, 80, 37-42. Manno, B., & Marston, A. R. Weight reduction as a function of negative covert reinforcement (sensitization) versus positive covert reinforcement. Behaviour Research and Therapy, 1972, 10, 201-207. McFall, R. M., & Hammen, C. L. Motivation, structure, and self-monitoring: The role of nonspecific factors in smoking reduction. Journal of Consulting and Clinical Psychology, 1971, 37, 80-86. McNamara, J. R. The use of self-monitoring techniques to treat nailbiting. Behaviour Research and Therapy, 1972, 10, 193-194. Smith, M. Effectiveness of symptomatic treatment of nailbiting in college students. Psychological Newsletter, 1957, 8, 219-231. Stephen, L. S., & Koenig, K. P. Habit modification through threatened loss of money. Behaviour Research and Therapy, 1970, 8, 211-212. FINAL ACCEPTANCE:NOVEMBER 1, 1975
(1976)
Covert Sensitization and Information in the Reduction of Nailbiting A N N A - M A R I E DAVIDSON AND DOUGLAS R . D E N N E Y
University of Kansas The relative effectiveness of covert sensitization and information in bringing about a reduction in nailbiting was investigated. The information procedure was devised as an attention-placebo treatment which was equated with covert sensitization in terms of nonspecific treatment factors such as demand, expectancy, and the degree to which attention was focused upon ones nails. Three treatment groups, covert sensitization, information, and combined treatment, were compared with a waiting-list control group in a 2 (Covert Sensitization) x 2 (Information) design. The dependent variable was the length of subjects' nails measured at a pre-test, post-test, and 5-week follow-up test. Contrary to prediction, covert sensitization did not emerge as a significant treatment procedure, and information did. Nonspecific treatment factors appeared to be sufficient to bring about substantial increases in the length of subjects' nails, and there was no evidence that covert sensitization improved upon the contribution of these nonspecific factors.
Estimates of the prevalence of nailbiting among college students indicate nailbiting to be a behavioral problem of some magnitude, affecting about 27% of this population (e.g., Coleman & McCalley, 1948). Techniques reported to be successful in treating nailbiting include the use of bitter substances applied to the nails (BiUig, 1941; Blount, 1931), negative practice (Dunlap, 1932; Smith, 1957), hypnotic suggestion (Gruenewald, 1965), self-administered electric shocks (Bucher, 1968), self-monitoring and the substitution of incompatible responses (Azrin & Nunn, 1973; Horan, Hoffman, & Macri, 1974; McNamara, 1972), and response-cost procedures (Stephens & Koenig, 1970). Most of the above studies constitute little more than demonstrations of the application of each procedure to nailbiting. When adequate controls have been employed, results generally indicate that nonspecific treatment factors (e.g., expectancy and demand characteristics, attention to the nailbiting behavior, periodic examinations of subjects' nails) are sufficient to account for improvement. For example, Stephens and Koenig (1970) compared various response cost schedules in reducing nailbiting. Subjects in three groups had their monetary deposits returned according to three different schedules contingent upon not biting their nails. A fourth group Requests for reprints should be addressed to Douglas R. Denney, Department of Psychology, University of Kansas, Lawrence, KS 66045. 512 Copyright © 1976 by Association for Advancement of Behavior Therapy. All rights of reproduction in any form reserved.
COVERT SENSITIZATION AND NAILBITING
513
had their deposits returned contingent only upon appearing for each weekly appointment to have their nails measured. All four groups showed significant improvement from the pre- to the post-test, and although somewhat diminished, these improvements were still intact after a 3-month follow-up period. However, no significant difference was found between the four groups. In addition, McNamara (1972) studied four treatments procedures which combined self-monitoring and the substitution of incompatible responses (e.g., finger tapping). These four treatments were compared with a measurement-only group and a group explicitly told to continue biting their nails and to record this behavior. Significant increases in nail length occurred in all six groups, and again no significant difference was found between the groups. Covert sensitization has been successfully employed in reducing a wide variety of problem behaviors including "oral" habits such as smoking (Cautela, 1970), alcoholism (Ashem & Donner, 1968), and overeating (Janda & Rimm, 1972; Manno & Marston, 1972). Covert sensitization might also be an effective procedure for bringing about reductions in nailbiting beyond those attributable merely to nonspecific treatment factors. Thus, in the present study, covert sensitization therapy was compared with an informational therapy designed to equal the former in terms of the degree to which subjects were led to expect success and to focus attention upon their nails. The informational therapy did include general educational materials concerning nails (e.g., cosmetic care and composition of the nails, dietary hints, nail diseases) but the information was not specific to nailbiting. No mention of nailbiting and no direct attempt to impel subjects to stop biting their nails were included. To analyze the separate contributions made by the covert sensitization and information procedures within the study, a 2 (Covert Sensitization) × 2 (Information) design was employed in which covert sensitization, information, combined covert sensitization plus information, and waiting-list control groups were compared. The three treatment procedures were automated to standardize these procedures and to facilitate their group administration. A significant main effect for covert sensitization would indicate that this component had made an independent contribution to the effectiveness of the treatment. METHOD Subjects. Thirty-three subjects participated, with 19 females and 12 males completing the program. The subjects, ranging in age from 17 to 26 years (.Y = 19 years), were students enrolled in General Psychology who indicated that they had a problem with nailbiting. Participation satisfied a course-related research requirement. A pre-test questionnaire showed that, although 20% of the subjects had no recollection of when they had begun biting their nails, 74% estimated that they had begun before the age of 11. Forty-five percent claimed to engage in nailbiting more than 10 times a day, and all of them considered their nailbiting to
514
DAVIDSON AND DENNEY
be a serious problem which they were highly motivated to overcome. Seventy-seven percent had previously refrained from nailbiting long enough to notice an appreciable change in the conditions of their nails. Pre-testing. Each subject attended a group pre-test session during which his nails were measured to the nearest millimeter using a Verneer caliper. Nail length measurements were taken at the center of each nail, from the tip of the nail to base of the cuticle. The measurements were summed across all 10 of the subject's nails. Subjects also completed a preliminary questionnaire concerning previous nailbiting histories. Treatment. Subjects were randomly assigned to four groups: covert sensitization, information, combined treatment, and waiting-list control. Subjects in the first three groups were given eight treatment sessions, conducted twice weekly. During each treatment session, subjects were seated in semiprivate cubicles in a secluded room in the University language laboratory. Each subject wore headphones and listened to prerecorded treatments transmitted from a central control room. Covert sensitization. The covert sensitization tapes l a s t e d about 15 minutes, the first beginning with a brief rationale describing aversive conditioning. All eight tapes included brief relaxation exercises, followed by an aversive scene and an aversion-relief scene. 1 In the aversive scene, the subject was depicted as engaging in a series of responses leading up to and including nailbiting and then suffering graphically described aversive consequences such as nausea, vomitting, bleeding, and social disapproval. In the aversion-relief scene, the subject was depicted as starting to engage in nailbiting, beginning to feel nauseated, refraining from nailbiting and engaging in some incompatible behavior (e.g., breathing exercises, circulation exercises involving the hands), and feeling instantaneous relief and pride. Study-related situations were emphasized in several scenes, although a variety of additional problem situations conducive to nailbiting were also included. Generally, as the sessions progressed, the subject was depicted as becoming more adept at discriminating behaviors immediately preceding nailbiting and interrupting the chain at earlier points during the aversion-relief scenes. Information. The information tapes were also about 15 minutes in duration, the first beginning with a brief rationale suggesting that a change in attitude toward one's nails might reduce nailbiting. Topics covered on the eight tapes included (a) facts about nails, (b) the names of various parts of nails and cuticles, (c) nail care and manicure techniques, (d) prevention and repair of nail damage, (e) application of artificial nails, and (f) nail diseases. Combined treatment. Within each of eight sessions in this treatment, subjects received first the information and then the covert sensitization tape. Waiting list control. Subjects were told they would not receive treatment until later in the semester. Their nails were measured during the pre-test and the post-test sessions, but they received no intervening treatment. Following the post-test, the subjects were treated with the combined treatment procedure, and their nails were again measured during a 5-week followup session. Post-testing. All subjects' nails were again measured at a post-test session six weeks after the pre-test, and control subjects were scheduled for their forthcoming treatment sessions. Treated subjects completed a brief post-treatment questionnaire concerning their treatmentrelated behaviors during the course of therapy. A follow-up session was held five weeks after the post-test session. Nails were again measured. In addition, the control subjects, who had just completed their treatments, were asked to complete the post-treatment questionnaire. A transcript of one of the scenes employed in the covert sensitization therapy is available upon request.
COVERT SENSITIZATION AND NAILBITING
5 15
RESULTS Preliminary analyses indicated no significant difference between males and females in pre-test scores or changes from pre- to post-test. A 2(Covert Sensitization) × 2(Information) analysis of variance performed on the pre-test scores revealed no significant pre-test difference among the four groups. A 2(Covert Sensitization) × 2(Information) x 2(Trials) analysis of variance was then performed on the pre- and the post-test nail length measures. A significant main effect for Trials, F(1,27) = 32.80, p < .001, and a significant Information x Trials interaction, F(1,27) = 12.54, p < .005, were obtained. Although the pre-test measures did not differ significantly, a 2(Covert Sensitization) × 2(Information) analysis of covariance was performed on the post-test measures using the pre-test measures as covariate to correct for slight initial group differences. Information was the only significantly effective treatment component, F(1,27) = 12.71, p < .005. A one-way analysis of covariance applied to the post-test measures revealed a significant main effect for treatments, F(3,26) = 5.97,p < .005, which was analyzed further using Tukey B tests. Only the information group differed significantly (p < .05) from the waiting-list controls. A 3 (Treatments) × 2 (Trials) analysis of variance was performed on the nail length measures from the pre-test and the follow-up test sessions. The waiting-list Control subjects were excluded from this analysis since they had received treatment between the post-test and the follow-up test ses-
TABLE 1 MEANS AND STANDARD DEVISIONS OF NAIL LENGTH MEASURES (IN CENTIMETERS) Covert sensitization
Information
Combined treatment
Waiting-list controls
Preh test: x SD
10.25 1.65
10.01 1.78
9.27 2.17
9.02 1.97
Post test x SD
11.05 1.74
11.42 2.44
10.62 2.53
8.87 1.75
Follow-up test: x SD
11.27 1.87
11.49 2.28
11.08 3.03
10.79 2.11
Note. The treatment group Ns are 7 (covert sensitization), 8 (information), 7 (combined), and 9 (waiting-list control). Unweighted means were used in all the analyses.
516
DAVIDSON AND DENNEY
sions and therefore no longer represented an adequate baseline control group. This analysis revealed only a significant main effect for Trials, F (1, 19) = 32.07, p < .001. Subjects in the three treatment groups improved significantly from the pre-test to the follow-up test, and there was no differential effect among the three treatments. For the waiting-list control subjects, a significant decrease in nail length occurred between pre- and the post-test sessions, t (8) = 2.94, p < .02. However, a significant increase in nail length occurred from the post-test to the follow-up test, t (8) = 5.59, p < .001, and from the pre-test to the follow-up test, t (8) = 4.73, p < . 002. These increases are attributable to the combined treatment which control subjects received following the posttest session. Data from the preliminary questionnaire were analyzed in relation to changes in nail length measures over the course of treatment. Neither sex nor any of the variables extracted from the preliminary questionnaire (age at which nailbiting began, frequency with which nailbiting occurred each day, previous spontaneous attempts to stop nailbiting, perceived seriousness of ones nailbiting problem) were significantly related to improvement during treatment. DISCUSSION Contrary to prediction, covert sensitization did not contribute significantly to the improvement in nail length measures over the course of treatment. Furthermore, on the basis of specific comparisons between each treatment group and the control group, covert sensitization may have actually detracted from the effectiveness of information alone. The information group was the only group that differed significantly from controls at the time of the post-test. Comparisons among the three treatment groups revealed no significant difference at either post-test or follow-up, consistent with earlier studies (McNamara, 1972; Stephens & Koenig, 1970) and again indicating that nonspecific treatment factors alone may be principally responsible for improvements in subjects' nails. Clearly, covert sensitization did not enhance treatment effectiveness beyond that attributable to nonspecific treatment factors such as demand, expectancy, and attention to one's nails. The covert sensitization procedure was group administered and made use of standardized scenes. It might be argued that a more individualized procedure would have been more successful. However, although the relative efficacy of group vs. individual administrations of covert sensitization has not been studied, several investigators (e.g., Janda & Rimm, 1972; Manno & Marston, 1972) have reported successes using group administered covert sensitization. One might also argue that eight treatment sessions were too few for covert sensitization to emerge as a definitive treat-
COVERT SENSITIZATION AND NAILBITING
517
ment for nailbiting, although here again, other investigators focusing on other problems have reported successes using even fewer sessions (e.g., Janda & Rimm, 1972; Manno & Marston, 1972). The most cogent explanation for the present results is that nailbiting behaviors are so readily altered by nonspecific treatment factors that these factors alone are sufficient to bring about substantial changes in nail length. Within this context, covert sensitization could not be distinguished as an effective procedure. This explanation also has merit in terms of accounting for the lack of change in the waiting-list control group from the pre-test to the post-test. The untreated groups in the present study and in Smith's (1957) study did not improve between the pre-test and the post-test. However, both Stephens and Koenig (1970) and McNamara (1972) reported significant improvements for their untreated control groups. The difference seems to lie in how frequently subjects' nails were measured and whether the subjects believed themselves to be receiving treatment. In the latter two studies, subjects' nails were measured frequently and it seems quite obvious that subjects believed they were receiving treatment. In the present study, and presumably Smith's study, control subjects' nails were measured only twice and-subjects were explicitly told they were in a control group. The differences in nonspecific treatment factors such as attention, demand, and expectancy seem to account for the differences between these two types of untreated control groups. Once again, nonspecific treatment factors appear to be sufficient to bring about successful changes in subjects' nailbiting problem. The situation for nailbiting is not unlike that for smoking. Recent reviews (e.g., Hunt & Matarazzo, 1973; McFall & Hammen, 1971) indicate that almost any type of treatment is effective in bringing about substantial decreases in cigarette consumption from the pre- to the post-test. In the case of smoking, the problem becomes one of maintaining the initial treatment results over an extended follow-up period. Similarly, the present study, along with others, indicates that nailbiting is readily decreased from the pre- to the post-test by almost any treatment which focuses interest upon one's nails and contributes to subjects' expectancies for change. While these decreases were maintained intact during a five-week follow-up period, the question remains whether the nailbiting habit would reoccur over a more extended period, especially one in which subjects no longer expected their nails to be measured. REFERENCES Ashem, B., & Donner, L. Covert sensitization with alcoholics: A controlled replication. Behavior Research and Therapy, 1968, 6, 7-12.
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