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Habit Reversal Training: A Behavioural Intervention to Decrease Nail Biting

Info: 7310 words (29 pages) Dissertation
Published: 1st Sep 2021

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Tagged: Psychology


This case study of a 25-year-old participant with a significant nail-biting (NB) habit, examines the effect of Habit Reversal Training (HRT) on the frequency of NB over 28 days (ABAB design, 7 days each condition).  The HRT intervention utilized awareness training, relaxation techniques, a more socially acceptable competing response of chewing gum, and contingency management via differential reinforcement of low rates of behavior (DRL).  NB daily mean frequency data was recorded by the participant using self-observation, as well as observation data conducted by a cohabitant for inter-rater reliability comparison.  At the end of each baseline and each intervention phase, pictures of the participant’s fingernails were taken for self-appraised comparison at the end of the study. Results indicated that the frequency of the participant’s NB reduced by 34.43% during intervention phases and the participant appraised her nails as most improved during both intervention periods.


Nail biting (NB) is a chronic habit similar to other body-focused repetitive behaviors (BFRBs), such as hair pulling (trichotillomania) and skin picking (excoriation) disorders in the Diagnostic and Statistical Manual for Mental Disorders-Fifth Edition (DSM-5; American Psychiatric Association, 2013; Roberts, O’Connor, & Belanger, 2013).  Although not a diagnosis in the DSM-5, NB is a habitual, problematic, and harmful self-directed behavior that may be classified as impulse control disorder not otherwise specified (Moritz, Treszl, & Rufer, 2011).  The function of this behavior and its origin has been explained by many different theories.  Many different treatment methods have been developed to combat this potentially harmful habit (Dufrene, Watson, & Kazmerski, 2008).

NB may cause damage to nail tissue, infection, and tooth damage (Dufrene et al., 2008).  NB has been associated with somatic complaints and decreased well-being (Moritz et al., 2011).  NB is also related to weaker social abilities (Ghanizadeh, & Shekoohi, 2011).  Williams, Rose, and Chisholm (2007) found that NB occurred more frequently in a sample of adolescents when they were required to solve difficult problems or when they were bored.  They propose that specific inner emotional states reinforce or set the stage for NB to occur.  NB was least likely to occur when engaged in social interaction or when punished by others (Williams et al., 2007).  NB may maladaptively serve the function of emotional regulation (Roberts et al., 2013).

The function of the NB behavior must be understood before change can be effectively implemented(Williams et al., 2007).  Several theories have been proposed regarding the function and origin of NB.  It was hypothesized that NB occurs as the result of or co-occurring with psychiatric disorders (Ghanizadeh, 2008); however, there is limited research regarding the impairment linked to BFRBs (Hayes et al., 2009).  Ghanizadeh (2008) found that NB was most likely to occur in individuals with attention-deficit hyperactivity disorder, followed by oppositional defiant disorder, separation anxiety disorder, enuresis, tic disorder, and obsessive-compulsive disorder.  Individuals with NB perceived that they had limited control over the behavior, as well as over the physical and psychological consequences of the behavior (Roberts et al., 2013).  Although NB was typically thought to reduce anxiety and tension, studies do not support this theory (Ghanizadeh, 2011).  It has also been suggested that NB may be attributed to an obsessive-compulsive disorder or may be a habit rather than the result of an emotional condition (Ghanizadeh, 2011).

What has been deemed a “nervous habit,” is often seen in non-clinical populations and is typically thought of as common or not harmful (Hayes, Storch, & Berlanga, 2009).  BFRBs, such as NB, may be viewed as non-functional at a superficial level, yet they do allow for affect regulation at a deeper level of analysis (Stein et al., 2008).  Research by Teng, Woods, Twohig and Marcks (2002) found that 13.7% of a general, non-clinical sample of 105 college students performed at least one bodily-focused repetitive behavior (BFRB), nail-biting being the most common BFRB experienced.  Dufrene et al. (2008) also stated that the participant used in their case study did not positively screen for clinical levels of anxiety or depression measured via the State Trait Anxiety Inventory (STAI; STAI Forms Y-1 and Y-2; Spielberger, Gorsuch, Lushene, Vagg, & Jacobs, 1983) and the Beck Depression Inventory-II (BDI- II; Beck, Steer, & Brown, 1996), yet she had been exhibiting NB since early adolescence.

All BFRBs similarly present with onset during adolescence and appear to be responsive to behavioral modification treatment (Stein et al., 2008; Bohne, Keuthen, & Wilhelm, 2005).  Punishment has not been effective in the treatment of NB and may actually lead to an increase in NB frequency (Ghanizadeh, 2011).  Ghanizadeh (2011) found that snapping a hairband worn on the wrist as a form of punishment for NB was ineffective or only as effective as a placebo (Ghanizadeh, 2011).  Other methods used to treat NB include chewing gum or wearing a rubber band on the wrist as a reminder cue (Ghanizadeh, 2011).  A hairband or rubber band may be used as a non-removable reminder (NrRs) (Koritzky, & Yechiam, 2011).  In a study utilizing NrRs to treat NB, NrRs were utilized as a constant reminder of their goal to quit NB.  NrRs were found to be as effective as an aversion behavioral modification approach overall with a lower drop out rate (Koritzky, & Yechiam, 2011).  Bandura (1989), as discussed by Koritzky and Yechiam (2011), stated that behavior modification should be initiated and regulated by the individual to enhance a sense of self-efficacy and human agency and this process may be supplemented by memory cues, such as the hairband or rubber band.

Azrin and Nunn (1973) found that NB could be explained by response chaining, limited awareness, and excessive practice.  This theory helped derive another method of treatment for NB, a self-help intervention known as decoupling (DC) (Moritz et al., 2011).  Similar to Azrin and Nunn (1973), DC defined NB as a sequence of habitual motor behaviors that are broken down into segments and rearranged (Moritz et al., 2011).  Using 72 participants, Moritz et al. (2011) found that, when compared to progressive muscle relaxation (PMR), a relaxation technique focusing on tensing and releasing muscles groups in the body, those in a DC group showed greater control over the NB urge and displayed better progress in terms of self-appraisal of nail appearance by the end of the intervention.  Additionally, a competing response was also emphasized as an effective method of treatment for NB, such as writing, drawing, holding a ball, etc.; however, the efficacy of these approaches remain uncertain (Ghanizadeh, 2011).

Perhaps the most studied and well-supported NB intervention is habit reversal training (HRT) (Bate, Malouff, Thorsteinsson, & Bhullar, 2011).  When originally developed by Azrin and Nunn (1973), HRT included 11 major components for behavioral modification organized in five phases including: awareness training, relaxation training, competing response training, motivation procedures, and generalization training.  The modified and shortened approach consisted of awareness training, relaxation training, competing response training, and contingency management (Ghanizadeh, 2011).  Research conducted by Woods and Miltenberger (1995) showed that awareness training and a competing response were critical components of HRT necessary to effectively treat nervous habits.  McKinley (1985) similarly found that using awareness training and a competing response was comparably effective to the use of the complete HRT procedure proposed by Azrin and Nunn (1973).  By raising one’s awareness of the behavior, self-control and self-efficacy was expected to increase, as well as the ability to identify changes of inner states that may precipitate NB behavior (i.e., anxiety, stress, boredom, etc.) (Bate et al., 2011).  A behavior that was once automatic and habitual may be changed when intentionally brought to one’s awareness (Chambers, Lo, & Allen, 2008).  However, awareness training was not sufficient when administered alone (O’Connor, 2005).  Yet, another study by McGuire et al. (2014) found that HRT in its entirety was only slightly more beneficial than awareness training alone (McGuire et al., 2014).

Other components of the modified version of HRT include relaxation training, competing response training, and contingency management (Ghanizadeh, 2011).  Different types of relaxation training are utilized, such as positive self-statements, visual imagery, PMR, and deep breathing (Ghanizadeh, 2011).  A more desirable competing response using antagonist muscles is also trained in order to make NB impossible and/or irrelevant (Bate et al., 2011).  Bate et al. (2011) asserted that the competing response should be opposite of the target behavior, maintained for an extended period of time, heighten awareness of the behavior, be more socially desirable, and be compatible with normal activity.  For example, Azrin and Nunn (1973) suggested grasping objects with one’s hands as a competing response to prevent NB.  Contingency management focuses on the inclusion of positive and negative reinforcement to foster long-term change, such as recruiting a significant other to provide positive reinforcement via encouragement and supportive statements/reminders (e.g., to use competing response or relaxation techniques) or negative reinforcement by reminding the client of the negative consequences of NB (e.g., pain, aesthetics, chipped teeth) that have since been eliminated or reduced since the onset of the intervention (Bate et al., 2011; Ghanizadeh, 2011).

Using components of HRT mentioned above, a meta-analysis by Bate et al. (2011) reviewed 18 different studies including 575 participants to determine the efficacy of HRT in the treatment of maladaptive, repetitive behaviors.  Overall, HRT showed a large effect size from pre- to post-treatment when compared to a control group and these results were generalized to a wide range of other maladaptive habitual behaviors (e.g., nail-biting, Tourette’s syndrome, trichotillomia, thumb sucking, etc.) (Bate et al., 2011).  A case study conducted on a habitual nail-biter found that NB decreased following HRT intervention as evidenced by nail growth and documented self-report (Dufrene et al., 2008).

HRT has also been found to successfully treat motor or vocal tics associated with Tourette’s Disorder, as well as decrease the frequency of nervous habits using only awareness training and a competing response (Miltenberger, 2011).  In a meta-analysis review of randomized controlled trials (RCTs), HRT with a comprehensive behavioral intervention, effectively reduced tic severity in those with Tourette’s Syndrome (McGuire et al., 2014).  Verdellen et al. (2011) researched 12 systematic reviews and eight randomized controlled trials and most evidence was found in support of HRT in the treatment of tic disorders.  HRT was found to be consistently efficacious when assessed using RCTs (McGuire et al., 2014).

Across most of the aforementioned studies utilizing HRT, an aspect of self-monitoring was incorporated, in which participants were required to record their behavior and self-administer the behavior modification techniques (Craig, 2010).  Self-observation and monitoring frequency of NB is thought to increase awareness and perceived control of the behavior (Bate et al., 2011).  However, this method of observation may introduce biases, such as inaccurate data, that may then influence the results of the study (Roberts & Neuringer, 1998). To address this challenge, other researchers have recorded self-monitoring procedures using tangible evidence to support self-observation data, such as the use of photographs to visually depict the effects of NB overtime (Christmann & Sommer, 1976; Ladouceur, 1979; Vargas & Adesso, 1976).  In a study by Ladouceur (1979), photographs of the participants’ hands were taken at baseline (before treatment) and again at 6 and 12 weeks following intervention.  Comparative self-appraisals were made regarding the participants’ nail length before and after treatment in an effort to evaluate treatment efficacy.  This is a common self-monitoring procedure in the literature for nail biting (Dufrene et al., 2008).

Therefore, it was hypothesized that, NB behaviors would decrease in mean daily frequency during intervention conditions utilizing HRT.  In addition, it was hypothesized that, when compared to the other two photographs from baseline conditions, the participant would choose the two pictures taken at the end of intervention conditions in which she appraised her nail growth to be most improved.



The participant was a 25-year-old, single, Hispanic female with a problematic NB habit.  She is currently a second-year clinical psychology doctoral student at Philadelphia College of Osteopathic Medicine.  She has never been treated for NB and has been biting her nails since she was three-years-old.  The participant did note that she began to experience tension, worry, and nervousness when she first began her doctoral program two years ago.  Since that time, her NB habit has significantly worsened.


Notebook for Self-Observed NB Frequency Data. The participant was asked to record the number of times (i.e., frequency) NB behavior occurred in a notebook within a two-hour period (from 7:00 PM to 9:00 PM) when she was most likely to be completing homework or working from home. A NB episode was defined as any contact between the participant’s nails and her teeth for at least a one-second period.

Observation Notebook of Participant’s NB Frequency by a Cohabitant. An individual who lives with the participant was also asked to record the number of times (i.e., frequency) the participant performed the target behavior of NB on a notebook within the same two-hour period (from 7:00 PM to 9:00 PM). Again, a NB episode was defined as any contact between the participant’s nails and her teeth for at least a one-second period. In order to ensure inter-rater reliability, frequency data from both the participant and the cohabitant were compared at the end of each of the four phases throughout the study.

Positive Self-Talk. As a form of relaxation, the participant was asked to continuously state aloud to herself “I can do this” and/or “I am strong enough to resist” when experiencing an urge to place her nails in her mouth or when experiencing stress or anxiety that may typically result in NB behavior. Positive self-statements were utilized by the participant each day for two hours (from 7:00 PM to 9:00 PM) during the intervention periods only (i.e., phase one and phase three).

Chewing Gum. The participant was asked to purchase a 60-piece pack of chewing gum.  One piece of gum was chewed by the participant at the beginning of each intervention-only phase (i.e., phase one and phase three). A new piece of gum was chewed by the participant each day for two hours (from 7:00 PM to 9:00 PM) during the intervention periods only (i.e., phase one and phase three).

Cookies. As a form of positive reinforcement and contingency management, the participant was allowed to eat one of her favorite type of cookies (Chips Ahoy chocolate chip cookies) when NB frequency was recorded by both the participant and cohabitant to be under 10 times within the allotted two hour period (from 7:00 PM to 9:00 PM) each day during the intervention periods only (i.e., phase one and phase three).

Cellphone Camera. In order to evaluate the participant’s progress throughout the study in an unbiased manner, cohabitant took pictures of the participant’s nails at the end of each of the four phases (i.e., ABAB), printed these four pictures, and presented these pictures to the participant at the end of the study without identifying when they were taken.  The participant then chose two pictures in which her nails appeared the most improved.


This study followed a single subject, ABAB design.  The target behavior that was treated using HRT was NB.  A modified version of the HRT intervention was utilized, which consisted of awareness training, relaxation training, competing response training, and contingency management (Ghanizadeh, 2011).  A NB episode was defined as any contact between the participant’s nails and her teeth for at least a one-second period (Roberts et al., 2013).  NB frequency was measured via self-monitoring data, as well as observation data recorded by a cohabitant. This cohabitant independently recorded NB frequency, which was then compared to self-monitored frequency at the end of each of the four phases of the study in order to ensure inter-rater reliability. Frequency of NB behavior was manually recorded by both the participant and the cohabitant on paper only within a specified two hour period, from 7:00 PM to 9:00 PM, each day of the study.  The study was continuously conducted for a period of 28 days, seven days each condition (four conditions total).

During the baseline phase of the study, the participant was asked to continue doing work from home as she normally does from 7:00 PM to 9:00 PM.  She and the cohabitant were asked to monitor and record the frequency of NB using data collection notepads.  On the eighth day of the study, the participant and cohabitant were again asked to monitor and record the frequency of NB within the allotted two hours; however, the intervention was utilized at this point in the study.  When the participant realized that she was performing the target behavior (NB), in addition to recording the frequency of the behavior, the participant was now asked to begin chewing gum at the beginning of the observation period (a competing response).  Chewing gum was trained to prevent the undesirable behavior of NB, while reducing tension and anxiety.  Also, by activating similar muscles to perform this more desirable behavior, this was proposed to contribute to increased awareness and serve a similar function.

Secondly, she was asked to utilize positive self-talk (e.g., “I can do this” or “I am strong enough to resist”) whenever she became aware of the urge to perform the target behavior during intervention periods only.  If the participant and cohabitant recorded NB frequency of 15 or below, she would reward her efforts with one of her favorite cookies at the end of the two-hour observation period on that day, as a form of contingency management via differential reinforcement of low rates of behavior.  After the second week, the third phase of the study began and the participant was asked to return to collecting baseline data.  Finally, the final phase of the study once again reintroduced the intervention for the final seven days of the study using the same procedures as the previous intervention phase.

At the end of each phase period (seven days), the cohabitant took a picture of the participant’s nails using a cellphone camera.  At the end of the study, without informing the participant when the pictures were taken, the participant chose two pictures that reflected the most progress in terms of nail growth.  This, in addition to patient and cohabitant’s observations of NB mean daily frequency, were used to determine the intervention’s efficacy.  The participant did not use any nail polish, nail growth polish, and/or artificial nails throughout the study as to not interrupt the natural growth of her nails.

Behavioral Conceptualization of Problem and Intervention

The target behavior of the patient’s functional analysis is nail-biting (NB).  A NB episode can be defined as any contact between the participant’s nails and her teeth for at least a one-second period (Roberts et al., 2013).  Typically, the participant engages in NB behavior when feeling tense, nervous, and/or bored.  Therefore, the antecedents that elicit the target behavior are inner states.  The NB behavior serves the function of releasing tension and alleviating boredom with movement.  Relative to these functions, NB is negatively reinforcing in that it removed an aversive stimulus (bored, nervousness, tension). Performing this behavior leads to at least a temporarily reinforcing consequence (no longer feeling negative emotional states).  Therefore, the behavior is becomes habitual because it must be continuously performed in order to remove or combat these persistent negative inner states when completing work on a daily basis (maintaining variable).  However, the behavior does also lead to several long-term, negative consequences, such as cracked teeth, nail pain, social undesirability, aesthetically unpleasing appearance of nails, and financial loss when attempting to correct the problem (e.g., nail growth polish, artificial nails, etc.).

Another maintaining antecedent for the behavior is the work/homework that elicits these negative inner states.  This antecedent also acted a setting event because it predicted the occurrence of the target behavior.  This antecedent cannot be changed or avoided because the participant is a full-time student and works from home part-time.  Since the antecedent of work itself was unchangeable, the only antecedent that was manipulated was the negative inner states that triggered the behavior (tension, anxiety, boredom).  As part of the intervention, the participant was asked to utilize a relaxation exercise that was also positively reinforcing (positive self-talk) to help her cope with these feelings elicited by homework/work, while also accepting, but not feeding into, the urge to perform the target behavior.

The main focus of intervention was to provide positive reinforcement for a competing, more desirable alternate behavior.  Since the behavior has become automatic and habitual, the HRT intervention was utilized in order to gain awareness of when the behavior occurs (awareness training) by having the participant monitor and record NB frequency.  The intervention also allowed the participant to engage in a competing behavior that is less damaging, more socially desirable, and served a similar function (chewing gum).  This alternate behavior was reinforcing by reducing boredom and tension in a similar fashion (oral satiation), while also using the same muscles that would make NB very difficult to perform simultaneously.  Ultimately, when NB was reduced in frequency at the end of each observation period during intervention phases, the participant was allowed to eat one cookie to positively reinforce her consistent use of the competing and desirable alternate behavior (positively reinforcing consequence).  This positive consequence (cookie) following maintenance of positive behavior over one session was used as a differential reinforcement of low rates of behavior procedure to positively reinforce decreased NB, while extinguishing this undesirable behavior.  She chose her favorite snack, a cookie, and her favorite brand of cookies (Chips Ahoy chocolate chip), in order to make this form of reinforcement personally salient.


The results of this study indicated that there was a decrease in NB during the intervention conditions compared to baseline conditions as shown in Table A.  During the first baseline condition, the mean frequency of NB behavior occurrence per day was 33.29, with a standard deviation of 1.91.  A decrease in frequency of NB behavior occurrence was evident during the second intervention condition with a mean of 24.43 per day, with a standard deviation of 3.70.  During the third phase when the participant returned to baseline using no intervention, the mean daily frequency of NB per day increased to 31.43, with a standard deviation of 1.50.  During the final phase of the study when the intervention was once again implemented, the mean daily frequency of NB decreased to 18.00, with a standard deviation of 4.14.  The mean daily frequency of the baseline conditions differed by 1.86, which indicated a 5.59% decrease from baseline one to baseline two.  The mean frequency of the intervention conditions differed by 6.43, indicating a 26.32% increase from intervention one to intervention two.  Additionally, the participant also obtained positive reinforcement (e.g., a cookie) on the final three days of the study, as her frequency scores were at 15 or below during the observation period on those days, which appeared to continuously reinforce a decrease in NB beginning at day 26 until the end of the study on day 28.

Figure 1 details the number of times NB behavior occurred per day during all conditions of the study.  Minimal differences were found in the number of times NB occurred during each intervention condition.  However, a clear difference was evident between baseline and intervention conditions, as represented on Table B (Baseline Weeks M= 32.36, SD= 1.95; Intervention Weeks M= 21.22, SD= 5.07).  The mean daily frequency difference between means from baseline weeks and intervention weeks was 11.14 (depicted in Figure 2).  These findings indicate that there was approximately a 34.43% decrease in the mean daily frequencyduring each intervention condition, as compared to each baseline condition (see Figure 3).  The rates of response during baseline conditions remained steady at a high rate of mean daily frequency of NB (as high as 36), but the rate of response by the participant showed continuously decreasing slopes across intervention conditions (with a mean daily frequency of NB as low as 13).  This steady decrease in response rate remained consistent when intervention was re-introduced.

No differences were found between participant’s self-observed data and cohabitant’s reported observation data.  A Cohen’s  was run to assess inter-rater reliability ( = 1.0).  This means that both observers’ ratings of mean frequency data of NB per day were in agreement 100% of the time.  Additionally, using a self-appraisal method of evaluation, the participant chose the two pictures taken at the end of intervention conditions, not from the baseline conditions, in which she appraised her nail growth to be most improved (represented below in Figures 4 and 5).


The results of this study provided support for the hypothesis that HRT would successfully decrease the mean daily frequency of NB during intervention conditions.  The decrease of NB from baseline to intervention conditions may be explained by the efficacy of the HRT intervention. The rates of response during baseline conditions remained steady at a high rate, but the rate of response by the participant continuously decreased across intervention conditions making it more likely that the intervention impacted the behavior over time.  This provided evidence of maintenance of gains over time across both intervention conditions.  Despite interruption by the second baseline condition, when the intervention was re-introduced at the end of the study, the participant’s response rates during HRT intervention was maintained at the same level as the prior intervention condition with continued decrease in responsiveness as the study approached termination.  Additionally, the second hypothesis was also supported.  When presented four pictures from each condition, two photographs taken at the end of both baseline conditions and two taken at the end of intervention conditions, the participant chose the two photos from the intervention conditions in which she appraised her nail growth to be most improved.

Results may have been more robust if positive reinforcement was provided at a more realistic schedule of reinforcement.  The required criteria of 15 or below mean daily frequency of NB for positive reinforcement (a cookie) was identified as a limitation of the study because the criteria for reinforcement was established at an unrealistically low number based on the initial severity of the participant’s NB behavior.  This overly strict criterion created an opportunity for reinforcement only toward the end of the study, as opposed to creating opportunities for reinforcement throughout the study.  It appears that mean daily frequency of NB continued to be at or below a frequency score of 15 upon her initial reinforcement with a cookie on day 26 of the study; therefore, we can assume that the positive reinforcement may have contributed to a successful decrease in the target behavior within the final three days of the study.  However, since she did not obtain this positive reinforcement until the last three days of the study, this intervention approach may not have been fully effective throughout the duration of the study and may have actually enhanced results if the required mean frequency schedule of NB was set at 20 instead of 15.  A more rapid decrease in the target behavior may have been observed if this number was adjusted to a more attainable, realistic ratio schedule for reinforcement at the beginning of the study.

A limitation of the study included an observer effect in which the participant’s knowledge of observation may have influenced the participant’s NB frequency.  This limitation was corrected by utilizing self-awareness via observation as part of the HRT intervention; self-awareness and self-observation were purported to increase self-control and self-efficacy (Bate et al., 2011).  Additionally, it was predicted that self-observation would be a limitation in terms of accuracy.  Therefore, to prevent any bias in data collection, the participant and a cohabitant recorded mean daily frequency data.  On each day of the study, their frequency scores were compared for inter-rater reliability.  Scores were found to be consistent between raters throughout each day of the study.

Moreover, the design of the study would make long-term generalization of these results difficult.  This was an ABAB design; therefore, there was no longitudinal component to this study to assess if results were maintained following termination of the study.  Given that the HRT intervention appeared to decrease the target behavior, it provides support that intervention was contributing to the changes in NB frequency over time.  However, generalization of these results or maintenance of gains for HRT may be difficult following termination.  During the study, HRT intervention observation periods were only conducted for a two-hour period each day.  It may be difficult to maintain HRT intervention components, such as self-monitoring via awareness training, competing response training, and contingency management, over a prolonged and indefinite period of time to sustain positive results and prevent relapse of NB.  Nevertheless, the HRT intervention is a cost-efficient method to combat NB as it is largely self-administered (Craig, 2010).  In order to reduce cost over time, the competing behavior of chewing gum may alternate with another competing behavior, such as grasping a stress ball.  The same would need to apply to contingency management via differential reinforcement of low rates of behavior (e.g., cookie); however, positive self-talk may also serve a similar, positively reinforcing function, in addition to being a relaxation technique.

Furthermore, the study was only conducted for four weeks and two weeks of the study were baseline in which no intervention was used.  Due to brief periods of intervention alternating with no-intervention baseline phases, the aesthetic benefits regarding progression of nail growth during intervention conditions were limited by length of time.  In order to prevent confounding variables contributing to intervention progress, the participant’s use of nail growth polish, colored nail polish, and/or artificial nails throughout the duration of the study was prohibited.  These items would have interrupted or artificially enhanced the natural growth of the nails during each phase of the intervention.  Future research should conduct HRT intervention over a more expansive period of time, in order to provide valuable visual evidence of nail growth progression in photographs.

This study’s results differed from previous literature on this topic in that there was limited, up-to-date research on HRT to treat NB alone.  HRT has typically been assessed when treating a wide range of habitual disorders, such as Tourette’s syndrome and other tic disorders (Bate et al., 2011; McGuire et al., 2014).  Therefore, further research must be conducted on HRT’s efficacy in the sole treatment of NB.  This study, although uniquely assessing the efficacy of HRT in the treatment of NB alone, used a single case study design, which lacks the generalizability necessary to make applicable treatment inferences.  Prior research on HRT in the treatment of many habitual disorders has been conducted using randomized controlled trials and psychometrically sound scales for measurement (Bate et al., 2011).  For example, studies measuring the efficacy of HRT for tic disorders utilized the Yale Global Tic Severity Scale (YGTSS; Leckman et al., 1989) to assess progression of this problem behavior over time (Wile & Pringsheim, 2013).  This case study did not include a control group for treatment efficacy comparison and did not utilize standardized measures.  These factors provide future study implications to increase overall generalizability and applicability based on this research.

Most of the available research on HRT for the treatment of nail biting is largely outdated and has been administered on clinical samples (Hayes et al., 2009).  Further research on this topic should include statistical support (e.g., effect size) for the efficacy of HRT with disorders other than tics (Bate et al., 2011).  Increasing knowledge regarding the etiology of nail biting as a BFRB may help to improve treatment, and possibly prevention, options for a variety of populations (Hayes et al., 2009).


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Table A

Nail Biting Mean of Daily Frequency and Standard Deviation

Condition Week Mean (SD)
Baseline 1 1 33.29 (1.91)
Intervention 1 2 24.43 (3.70)
Baseline 2 3 31.43 (1.50)
Intervention 2 4 18 (4.14)

Table B

Nail Biting Frequency Mean per Condition (Baseline verses Intervention)

Phase Week Mean (SD)
Baseline Weeks


Intervention Weeks

1 & 3


2 & 4

32.36 (1.95)


21.22 (5.07)

 Figure 1. Frequency of Nail Biting as a Function on Each Day of the Study


Figure 2. Mean of Daily Frequency of Nail-Biting between Baseline and Intervention Conditions


Figure 3. Comparison of Nail Biting Mean of Daily Frequency between Each Baseline and Intervention Condition


Figure 4. Pictures of nails at the end of baseline conditions.

Macintosh HD:Users:samanthaalgauer:Desktop:5b29313ee2f6b51c9db530d1d5f69c1a--bitten-nails-nail-care.jpg


Figure 5. Pictures of nails at the end of intervention conditions.

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