The Spanish version of the Skin Picking Impact Scale (SPIS) and its Short form (SPIS-S)

Introduction: The Skin Picking Impact Scale (SPIS) is a self-report rating scale that assess the psychosocial impact of excoriation disorder. In this study the SPIS was translated into Spanish and its reliability was measured. Similarly, its short version (SPIS-S) has been translated and tested. Methodology: The recruitment has been performed through a survey launched on social media. All subjects were older than18 years and self-reported being diagnosed with an excoriation disorder. 281 individuals were rated for the validation analysis. SPIS has been translated into Spanish and validated through an exploratory and confirmatory factorial analysis. Participants have been also scored with the Skin Picking Scale-Revised (SPS-R). Results: On factor at the exploratory factorial analysis has a raw eigenvalue greater than 1, with 65.5% of total variance. The confirmatory analysis confirmed that the scale is one-dimensional. Cronbach’s alpha also confirmed a good internal consistency (α=0.934 for the SPIS and α=0.882 for the SPIS-S). Scores between the two scales (SPIS and the SPS-R) have shown a good convergence (r=0.592, p<0.0001). Conclusion: The Spanish version of SPIS and its short version show good psychometric properties and adequately reproduce the onedimensional model of the original English version.


INTRODUCTION
Excoriation disorder (ED) is also well-known as compulsive skin-picking, pathological skin-picking, psychogenic excoriation, or dermatillomania (1)(2)(3). This condition is characterized by a recurrent picking of skin, leading to skin lesions and significant distress or functional impairment (3,4). Affected patients may show typical injuries, or report bleeding and pain after picking their skin (3). Even though the patient is aware of the self-destructiveness of this behavior, he/she shows poor control about it (5), despite having made repeated attempts to decrease or interrupt it.
ED is also associated with relevant impairment in the occupational, social and personal functioning. Symptoms cannot be better explained by the presence of another mental disorder, medical condition or substance use (6). The repetitive behavior may be carried out with nails or instruments (tweezers, needles, among others) and causes tissue damage, cellulite, deforming scars, in addition to significant aesthetic and emotional distress (7).
ED was considered as an impulse control disorder (8), although, according to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association (DSM 5), it is currently included in the obsessive-compulsive disorder and other related disorders section (6).
The assessment of ED is based on clinicianadministered and self-report rating scales. Selfadministered scales reported a high psychometric validity (9,10). Skin Picking Scale (SPS) and Skin Picking Impact Scale (SPIS) are self-administered scales for ED, and measure its clinical severity and related psychosocial impact, respectively (10,11). Nonetheless, both of them are not validated in Spanish. In this study the Skin Picking Impact Scale (SPIS) and its short version (SPIS-S) have been translated into Spanish and their reliability have been measured.
The assessment of ED is based on clinicianadministered and self-report rating scales (9,10,12). Among the clinician-administered rating scales, the Yale-Brown Obsessive-Compulsive Scale modified for neurotic excoriation and the Skin Picking Treatment Scale are available (13). Skin Picking Scale (SPS) and Skin Picking Impact Scale (SPIS) are self-administered scales for ED, measuring the clinical severity of the disorder and the psychosocial impact of it, respectively (12,14). Self-administered scales report a high psychometric validity (13). It is noteworthy that a correct assessment of ED patients may lead to tailored therapeutic options.

Participants
Participants were recruited through an Internet-based survey, spread through social media, during December 2020. All participants received complete information about the aim of the study, privacy and dataprocessing. No payment has been foreseen for completing the survey. Subjects were older than18 years and self-reported being diagnosed with an excoriation disorder, according to the criteria of the American Psychiatric Association, and accepted to participate in the study.
The sample size was calculated using the Epidat epidemiological package. Assuming an expected ED frequency of 5% (15), a confidence level of 95%, and a precision of 2.6%, the minimum sample was established in 270 participants. Finally, 637 subjects were surveyed. Of them, 281 subjects were selected as reporting current symptoms of ED.
Current symptoms were detected as the presence of positive answers to the following two questions: a) At present, do you perform recurrent skin picking, that causes tissue damage, bleeding, or pain? And, b) Do you experience discomfort or impairment resulting from this behavior? The Internet-based survey approach was used taking into account that there is supporting evidence that responses to online surveys may provide similar findings to those reported through "in person" samples (16).
In this research, all measures, conditions, data exclusions, and procedure for the determination of the sample size, to the best of our knowledge, have been reported.

Measures
The Skin Picking Impact Scale (SPIS) The SPIS is a self-administered rating scale that assesses the severity of ED in terms of psychosocial impact. The scale is composed of 10 items. Each item reports a score ranging from 0 to 5, with a total score ranging from 0 to 50 points. A score of 7 has been determined as the cut-off point from which the existence of a significant psychosocial impact is considered (10). The SPIS-S includes questions 2, 5, 6 and 7 of the original version, with the same scores as the extended version and good psychometric properties (17).
The SPIS has demonstrated good internal consistency in previous research (α = 0.93) (15). Cronbach's alpha for the current sample is described in the results section of the present study.
The Skin Picking Scale-Revised (SPS-R) The SPS-R is a revised version of the Skin Picking Scale (SPS). It is self-administered and assesses the severity of ED in the 7 days prior to the evaluation. The scale is composed of 8 items. Each item gets a score ranging from 0 to 4, with a total score ranging from 0 to 32 points. SPS-R explores two dimensions: (a) severity of symptoms (frequency and intensity of the urge to pick, time spent picking, and ability to control it); and, (b) the impairment due to skin picking (emotional distress, social avoidance, and skin damage due to skin picking) (9,14). In this study, the Spanish version of the SPS-R was used, which has demonstrated good validity and internal consistency (α = 0.884; 0.889) in previous samples (12,18). Cronbach's alpha for the current sample is described in the results section of the present study.

Translation process and validation
The translation process was divided in three phases: (a) the original English version (v1) was translated into Spanish (v2); (b) a bilingual expert translated back the Spanish version (v2) into English (v3); (c) finally, a native English speaker compared, sentence by sentence, the new translation (v3) with the original English version (v1), in order to verify if they were equivalent in meaning. Some changes or improvements were made after the comparison was made and the Spanish version was administered to 20 individuals, as a pilot test, in order to verify if the questionnaire was understandable. After the pilot test, the final Spanish version was obtained (Table 1).

Statistical analysis
To test the construct validity, the pertinence of performing an exploratory factor analysis was preliminary assessed using the Kaiser-Meyer-Olkin (KMO; SPSS software -version 23) test for sample adequacy and the Bartlett's Test of Sphericity. The sample was randomly divided into two subsamples, in which exploratory factorial analysis was performed with the afore-mentioned software and confirmatory factorial analysis was performed with JASP statistical software (version 0.10.2.0). Exploratory factorial analysis aimed to obtain the factorial structure, to be confirmed with confirmatory analysis. Exploratory factorial analysis was made using principal axis factoring with promax rotation, with a kappa value of 4. Confirmatory analysis was made through diagonally weighted least squares (DWLS) estimation procedure, taking into consideration the sample size.
Chi square test was performed, and the following fit indices were used to assess the model: CFI, NFI, and RMSEA. For the validity of model, CFI and NFI values had to be at least 0.90 and RMSEA value below 0.05 (19).

Ethical considerations
The study was approved by the Department of Psychiatry of the National University of Asunción, School of Medical Sciences (Paraguay). Data were treated with confidentiality, equality, and justice, respecting the Helsinki principles. Participants who required a feedback from the survey were invited to write down their email address and received information or specific helpful suggestions.

RESULTS
Kaiser-Meyer-Olkin (KMO) test was adequate (KMO=0.919) and sphericity tested significantly (p<0,0001). These results confirmed that the sample was adequate for a factorial analysis. Secondly, the sample was randomly divided into two subsamples (subsample 1, n=142; subsample 2, n=139), in order to perform exploratory and confirmatory factorial analysis.

Factorial analysis
Since only the first factor had a raw eigenvalue greater than the parallel random values, thus one factor was retained. Before extraction, this factor explained 65.5% of total variance. After extraction, this factor explained 62.3% of total variance. Communality values were acceptable, except for item 1 ( Table 2).

Internal consistency and correlation between factors
For the SPIS, Cronbach's alpha showed a valid internal consistency (α=0.934). It is of note that the deletion of the first item of the scale would rise Cronbach's alpha to α=0.941. SPIS-S Cronbach's alpha showed a valid internal consistency too (α=0.882). SPIS's mean score and standard deviation were 11.5±12.4.
For the SPS-R, Cronbach's alpha showed a valid internal consistency too (α=0.889), the average score of the scale was 1.083, with a standard deviation of 0.907. The average correlation between items was 0.505. Scores between the two scales (SPIS and the SPS-R) have shown a good convergence (r = 0.592, p <0.0001), which indicates a direct and strong relationship between both scales and a good validity of the Spanish version of the SPIS.

DISCUSSION
Three elements are invariably observed in patients with ED (3,21): a) Recurrent skin picking, that causes tissue damage, bleeding, or pain; b) Significant discomfort or impairment resulting from skin picking; and, c) The behavior is not due to other medical or psychiatric illnesses or substance use (e.g., body dysmorphic disorder, amphetamine use, dermatological diseases, respectively).
The self-inflicted nature of skin lesions and the lack of delusions and/or hallucinations differentiate ED from other psychiatric conditions (such as delusional infestation) or dermatological diseases (such as dermatitis artefacta), which may lead to skin damage or mutilation (3). Skin picking is characterized by acute episodes with skin scratching, "digging" and damaging (22). The behavior may cause clinically significant injuries with preceding psychosocial stress in up to 90% of patients (22). Skin picking can be also ritualized, often at bedtime, and patients may feel unhappy and guilty for the disfigurement caused.
These negative feelings increase progressively as the skin picking continues (4). Stress, sadness, anger, anxiety, or specific situations like talking on the phone, being in bed, reading, or watching television can facilitate skin picking episodes (23).
Our results show that the Spanish version of SPIS reports acceptable psychometric properties and validity in terms of reliability and internal consistency. As in the original English version (14), in the Spanish version one well defined factor was found, with good factorial weights.
Regarding the confirmation analysis, all indices give acceptable values that confirm the model, which implies that the scale fully reproduces the original model of the authors. Internal consistency was correct and concordant with what the original authors reported. The same applies for the short version of the scale (10,17).
Finally, good convergence was found between the scores of the SPIS and the SPS-R, which indicates a direct and strong relationship between both scales and a good validity of the Spanish version of the SPIS. These results are consistent with the existing literature (15,24).
Limitations of this research may include the lack of data in order to determine if there were any other difference in sociodemographic factors (e.g., race, ethnicity, education level, employment, etc.) or clinical characteristics (e.g., comorbidity, urge to pick skin, etc.) that might be present between the included participants and the excluded subjects. Furthermore, the scope of this article could have been greater if additional data had been available (e.g., information on discriminant association with other obsessivecompulsive related disorders or emotional disorders). Another limitation may include the fact that we completely relied on self-report measures in order to include/exclude participants. Finally, test-retest reliability was not calculated, since contact information of recruited subjects were not collected for a second assessment.
A strength point of this research is the measurement of psychometric properties of the Spanish version of SPIS: this might suggest a valuable assessment tool for Spanish-speaking patients affected by ED. In fact, if not correctly assessed, diagnosed and successfully treated, ED may evolve into a chronic form with severe psychosocial impairment and serious medical complications. Clinicians would need an assessment instrument for ED (such as SPIS, possibly standardized according to the international guidelines). Also, therapeutic approaches should address the control of this repetitive behavior (picking), in order to improve patients' quality of life in the long-term (25).
Finally, we believe that the assessment of ED patients is useful to tailor therapeutic options on the base of patients' needs. It is also recommended that, whenever possible, patients are assessed with more tools, in order to guarantee an integral assessment over all stages of illness (13,18