Estimating the burden of vitiligo: a systematic review and modelling study.

BACKGROUND: Vitiligo is a chronic autoimmune disease characterised by depigmented skin patches, which can pose substantial psychosocial challenges particularly in individuals with dark skin tones. Despite its impact on quality of life, there is an absence of standardised global epidemiological data. We sought to address this gap with the present study. METHODS: In this study we did a systematic review and modelling analysis to estimate the global, regional, and national prevalence and incidence of vitiligo. We did a comprehensive search of nine digital libraries (PubMed, Embase, Web of Science, Scientific Electronic Library Online, KCI Korean Journal Database, Russian Science Citation Index, Western Pacific Region Index Medicus, Informit, and Health Research and Development Information Network) from inception up to May 25, 2023. We included cross-sectional or cohort studies reporting the incidence rate or prevalence of vitiligo, or data from which incidence rate or prevalence could be calculated, in the general population of a country or area of a country. Summary estimate data were extracted. A main outcome was to estimate the worldwide, regional, and country-specific lifetime prevalence of vitiligo diagnosed by physicians or dermatologists among the general population and in adults and children (as per age groups defined in included studies). We used a Bayesian hierarchical linear mixed model to estimate prevalence, and calculated number of affected individuals using the UN population structure in 2022. In estimating lifetime prevalence, studies reporting point or period prevalence were excluded. Our other main outcome was to estimate incidence rates of vitiligo, but due to a small number of studies, the data on incidence were presented in a descriptive summary. This study was registered on PROSPERO, CRD42023390433. FINDINGS: Our search identified 22 192 records, of which 90 studies met our inclusion criteria. Of these studies, six focused on the incidence of vitiligo, 79 reported on the prevalence of vitiligo, and five provided data on both incidence and prevalence. 71 studies reported on lifetime prevalence. In the most recent years studied, incidence rates in the general population ranged from 24·7 cases (95% CI 24·3-25·2) per 100 000 person-years in South Korea in 2019, to 61·0 cases (60·6-61·4) in the USA in 2017. In individual studies, incidence rates showed an increasing trend over the periods studied. The global lifetime prevalence of vitiligo diagnosed by a physician or dermatologist was estimated at 0·36% (95% credible interval [CrI] 0·24-0·54) in the general population (28·5 million people [95% CrI 18·9-42·6]), 0·67% (0·43-1·07) in the adult population (37·1 million adults [23·9-58·9]), and 0·24% (0·16-0·37) in the child population (5·8 million children [3·8-8·9]). Vitiligo prevalence was higher in adults than in children across all regions. Central Europe and south Asia reported the highest prevalence (0·52% [0·28-1·07] and 0·52% [0·33-0·82], respectively, in the general population). INTERPRETATION: This study highlights the need for standardised epidemiological data collection globally to inform public health policies and improve vitiligo diagnosis and management. Emphasis on the impact on individuals with darker skin tones is crucial to reducing stigma and improving quality of life. Furthermore, our study highlights the need to conduct more research in regions and populations that have been historically under-represented, to effectively address the worldwide burden of vitiligo. FUNDING: None.

Economic Burden among Patients with Vitiligo in the United States: A Retrospective Database Claims Study.

Patients with vitiligo incur direct and indirect costs associated with their condition; however, data regarding the economic burden of vitiligo are scarce and outdated. In this retrospective cohort analysis of the Merative MarketScan Commercial Database, healthcare costs and healthcare resource utilization (HCRU) were evaluated among United States patients with vitiligo. Patients with vitiligo were matched (1:2) with individuals without vitiligo (controls) between January 2007 and December 2021. Outcomes included all-cause and vitiligo-related costs (2021 dollars) and all-cause HCRU, including mental health-related HCRU, during a 1-year postindex period. Subgroup analyses were completed for patients on vitiligo treatments with systemic effects (such as phototherapy and oral steroids) or a new mental health diagnosis. The analysis was focused solely on direct costs. Baseline demographics were well-balanced between matched vitiligo (49,512) and control (99,024) cohorts. Patients with vitiligo incurred significantly higher all-cause ($15,551 vs $7735) and vitiligo-related ($3490 vs $54) costs than controls (P < .0001). All-cause and mental health-related HCRU were also significantly higher among patients with vitiligo (P < .0001). Differences in all-cause and vitiligo-related healthcare costs remained significantly higher in patients on treatments with systemic effects/mental health diagnoses than in controls (P < .0001). Taken together, healthcare costs and HCRU were significantly higher among patients with vitiligo than among controls.

Vitiligo patient population and disease burden in France: VIOLIN study results from the CONSTANCES cohort.

BACKGROUND: Vitiligo is a chronic autoimmune disease resulting in skin depigmentation. OBJECTIVES: This study assessed the prevalence, disease burden and treatment of vitiligo in France. METHODS: VIOLIN was a cross-sectional study nested in the national CONSTANCES cohort, which consists of randomly selected adults aged 18-69 years in France. In VIOLIN, longitudinal data were collected prospectively from 158,898 participants during 2012-2018 and linked to the National Health Data System (SNDS), a healthcare utilization database. Patients with physician-diagnosed vitiligo were matched (1:3) with control participants based on age, sex, geographic region, year of inclusion and skin phototype. Patients completed a questionnaire in 2022 to collect disease characteristics, disease burden and quality-of-life (QoL) data. RESULTS: Vitiligo prevalence was 0.71% (681/95,597) in 2018. The mean age in the vitiligo population was 51.2 years; 51.4% were women. Most patients (63%) were diagnosed before age 30 years, mainly by dermatologists (83.5%). Most patients (81.1%) had visible lesions (i.e. on face, hands). Vitiligo was limited to <10% of the body surface area (BSA) in 85.8% of patients. Comorbidities including thyroid disease (18.0% vs. 9.0%), psoriasis (13.7% vs. 9.7%), atopic dermatitis (12.4% vs. 10.3%), depression (18.2% vs. 14.6%) and alopecia areata (4.3% vs. 2.4%) were significantly more common in patients with vitiligo versus matched controls (n = 2043). QoL was significantly impaired in patients with >5% BSA involvement or visible lesions, particularly with ≥10% facial involvement. Vitiligo-specific instruments (i.e. Vitiligo Impact Patient scale and Vitiligo-specific QoL instrument) were more sensitive to QoL differences among subgroups versus general skin instruments, and generic instruments were least sensitive. Most patients (83.8%) did not receive any prescribed treatment. CONCLUSIONS: Patients with vitiligo in France have a high disease burden, particularly those with visible lesions or higher BSA involvement. Most patients are not receiving treatment, highlighting the need for new effective treatments and patient/physician education.

Clinician-reported outcome measures for the assessment of vitiligo: A scoping review.

Clinician-reported outcome measures (ClinROMs) are essential for assessment of vitiligo in clinical trials and daily practice. Several instruments have been developed and tested to measure, for example, vitiligo extent, repigmentation and activity. The goal of this review was to identify all introductory publications of ClinROMs for vitiligo that include at least some aspects of validation and to describe the instruments' characteristics, intention for use and practical strengths and limitations. A search strategy was conducted in PubMed, Embase and Cochrane Library (CENTRAL) from inception to July 2022. Based on the literature search (n = 2860), 10 articles were identified, describing 14 different ClinROMs. Six ClinRoms measured disease extent and/or repigmentation, seven evaluated disease activity and one was a composite score. The Vitiligo Area Scoring Index (VASI), and Vitiligo Extent Score (VES and VESplus) measure overall disease extent and/or repigmentation. The VASI relies on hand units (1% body surface area), whereas the VES and VESplus use a picture-based scoring technique. The Vitiligo Extent Score for a Target Area (VESTA) measures repigmentation percentage for target lesions. One global assessment score for extent has been validated. Vitiligo disease activity scores included a static measure of clinical activity signs (Vitiligo Signs of Activity Score [VSAS]) and two measures assessing dynamic evolution (Vitiligo Disease Activity Score [VDAS] and Vitiligo Disease Improvement Score [VDIS]). The Vitiligo European Task Force assessment tool (VETFa) is a composite score. Depending on the practical strengths and limitations as well as the research question and setting (clinical trials vs. daily practice), the choice of an appropriate ClinROM may differ. Fourteen ClinROMs in vitiligo were identified to measure vitiligo extent, repigmentation, and activity. Further research evaluating the validity, reliability, and responsiveness of each instrument and worldwide consensus on which instrument to use for a specific outcome (domain) is greatly needed.

Development and Validation of the Epidemiological Tattoo Assessment Tool to Assess Ink Exposure and Related Factors in Tattooed Populations for Medical Research: Cross-sectional Validation Study.

BACKGROUND: Tattooing, whose popularity is growing worldwide, is an invasive body art that involves the injection of chemical mixtures, the tattoo ink, into the upper layer of the dermis. Although these inks may contain environmental toxins, including known human carcinogens, their long-term health effects are poorly studied. To conduct the urgently required epidemiological studies on tattoos and their long-term health effects, a validated method for assessing the complex tattoo exposure is needed. OBJECTIVE: We aimed to develop and validate the Epidemiological Tattoo Assessment Tool (EpiTAT), a questionnaire to self-assess tattoo ink exposure in tattooed populations suitable for application in large epidemiological cohort studies. METHODS: One of 3 preliminary versions of the EpiTAT using one of the alternative tattoo measurement units hand surface, credit card, or body schemes was randomly filled in by tattooed volunteers in Lyon, France. To identify the most suitable unit of tattoo self-assessment, a validation study was conducted with the selected respondents (N=97) to compare the self-assessments of tattoo surface, color, and coverage with validation measurements made by trained study personnel. Intraclass correlation, the Kendall rank correlation, and 2-tailed t tests were used to statistically compare tattoo size, color area, and tattoo coverage separately for each questionnaire version. Participants' opinions on the alternative measurement units were also considered in the overall evaluation. For quality control of the validation measures, digital surface analysis of 62 photographs of selected tattoos was performed using Fiji/ImageJ. RESULTS: In general, the results revealed overestimation of self-assessed measures compared with validation measures (eg, mean tattooed body surface 1768, SD 1547, cm2 vs 930, SD 1047, cm2, respectively, for hand surface; P<.001) and validation measures compared with digital image analysis (mean individual tattoo surface 147, SD 303.9, cm2 vs 101, SD 154.7, cm2, respectively; P=.05). Although the measurement unit credit card yielded the most accurate measures for all variables of interest, it had a much lower completion rate (78/129, 60.5%) than hand surface (89/104, 85.6%) and body schemes (90/106, 84.9%). Hand surface measured total tattoo size more accurately than body schemes (absolute agreement intraclass correlation coefficient: 0.71 vs 0.64, respectively). CONCLUSIONS: The final version of the EpiTAT contains 21 items and uses hand surface as a visual unit of measurement. Likert scales are used to assess color and coverage as a proportion of the total tattoo area. The overestimation of tattoo size by self-reporting merits further research to identify potential influential factors or predictive patterns that could be considered when calculating exposure.

Patient Unique Stigmatization Holistic tool in dermatology (PUSH-D): Development and validation of a dermatology-specific stigmatization assessment tool.

BACKGROUND: The skin plays an important role in establishing interpersonal relationships, and thus visible skin disorders, which have a significant impact on physical appearance, influence other people's behaviours and attitudes. OBJECTIVE: To develop and validate a dermatologic-specific questionnaire to evaluate stigmatization in individuals with visible skin conditions. METHODS: Items were generated by a verbatim report based on qualitative interviews with patients with various dermatologic conditions. Subsequently, a study was implemented for psychometric analysis. A dermatology-specific stigmatization questionnaire (PUSH-D) was refined via item reduction according to inter-question correlations, consensus among experts and exploratory factor analysis. Internal consistency was determined by calculating Cronbach's α. Concurrent validity was determined by calculating the correlation between PUSH-D and the Dermatology Life Quality Index (DLQI) and the Rosenberg Self-Esteem Scale (RSES). RESULTS: From a primary list of 22 items, PUSH-D was reduced to a 17-item questionnaire, covering two pertinent dimensions based on the exploratory factor analysis. Construct validity was demonstrated, and PUSH-D showed good internal consistency (Cronbach's α = 0.9). PUSH-D correlated strongly with the DLQI 0.72 (p < 0.001) and moderately with the RSES 0.49 (p < 0.001). CONCLUSION: PUSH-D allows a comprehensive view of the degree of stigmatization in visible skin disorders, as well as the comparability of stigmatization levels across various skin conditions.

Validation of a physician global assessment tool for vitiligo extent: Results of an international vitiligo expert meeting.

Currently, vitiligo lacks a validated Physician Global Assessment (PGA) for disease extent. This PGA can be used to stratify and interpret the numeric scores obtained by the Vitiligo Extent Score (VES). We investigated the interrater reliability of a 5-point PGA scale during an international vitiligo workshop. Vitiligo experts from five different continents rated photographs of non-segmental vitiligo patients with varying degrees of extent with the PGA score. Good interrater agreements (intraclass correlation coefficient >0.6) were observed between the raters overall and within each continent. All hypotheses to evaluate construct validity were confirmed. Median VES values per category were for limited 1.10 [IQR: 0.21-1.67], moderate 3.17 [IQR: 1.75-6.21], extensive 9.58 [IQR: 6.21-13.03] and very extensive 42.67 [IQR: 21.20-42.67]. Defined categories for vitiligo extent can be valuable for inclusion criteria and may impact future reimbursement criteria.

Burden of albinism: development and validation of a burden assessment tool.

BACKGROUND: Albinism comprises a group of autosomal recessive diseases that are characterized by poor vision and a variable hypopigmentation phenotype. A comprehensive literature review showed that no tool can assess the burden experienced by individuals who present with albinism, although such a tool is needed and would be beneficial for clinicians and patients alike. METHOD: The questionnaire was devised using standardized methodology for developing and validating questionnaires on the quality of life of subjects according to the following chronological structure: conceptual phase, development phase, and then validation phase. A multidisciplinary working group was assembled, including experts on questionnaire design and development, dermatologists specializing in care for patients with albinism, and representatives of the Genespoir association. RESULTS: Based on an initial verbatim report, the workgroup compiled a list of items that were transcribed and reformulated into questions. During the validation phase, principal component analysis (PCA) was conducted on the 24 items, which allowed the questionnaire to be reduced to 20 questions [Q]. The standardized regression coefficients were all greater than 0.5 for their corresponding factors. Based on their normalized regression coefficients, each group of questions was linked to one of the following four dimensions, with each dimension consisting of at least three questions: "Live with" (8 Q), "Daily life" (3 Q), "Resignation" (3 Q), and "Fear of the future" (6 Q). All dimensions correlated well with the overall BoA score. Cronbach's α was 0.92 for the entire BoA scale, confirming excellent internal coherence. Intradimensional coherences all demonstrated excellent reliability (α > 0.65). The BoA questionnaire was highly correlated with the SF12, RSES and DLQI validated questionnaires. This outcome confirmed the external validity. CONCLUSION: This questionnaire represents the first specific assessment tool for evaluating the burden of albinism. It is easy to use and relatively quick to complete, which will allow the burden to be evaluated over time with a reproducible questionnaire. To ensure that this questionnaire can be used by as many people as possible, cultural and linguistic validation in US English was conducted with the original French version.

Lessons of a day hospital: Comprehensive assessment of patients with albinism in a European setting.

Albinism is a rare genetic disease, comprising syndromic and non-syndromic forms. We assessed clinical and genetic characteristics in a prospective evaluation of 64 patients (33 children and 31 adults) seen at a specialized day hospital. Causative genetic mutations were found in TYR (23/64, 35.9%), OCA2 (19/64, 29.7%), TYRP1 (1/64, 1.6%), SLC45A2 (12/64, 18.7%), C10orf11 (1/64, 1.6%), HPS1 (3/64, 4.7%), HPS5 (1/64, 1.5%), HPS6 (1/64, 1.6%) and GPR143 (2/64, 3.1%). Causative mutations remained undetermined for one patient (1.6%). Heterogeneity for hair and skin phenotype was noted across and within the different genotypes. Skin and hair hypopigmentation did not correlate with visual impairment. The diagnosis of unrecognized syndromic forms and of cases of ocular albinism in this prospective and comprehensive series of patients with albinism in a European setting is remarkable. Photoprotection was overall good but not optimal.

Quality of Life, Burden of Disease, Co-morbidities, and Systemic Effects in Vitiligo Patients.

Vitiligo is a complex, systemic disease associated with many autoimmune and autoinflammatory conditions. Additionally, the cutaneous changes of vitiligo have significant effects on quality of life and self-esteem. Further efforts are needed to increase our understanding of vitiligo comorbidities as well as to increase awareness of the psychological effects of vitiligo.

Development and validation of a patient-reported outcome measure in vitiligo: The Self Assessment Vitiligo Extent Score (SA-VES).

BACKGROUND: The Vitiligo Extent Score (VES) has recently been introduced as a physicians' score for the clinical assessment of the extent of vitiligo, but a good patient self-assessment score is lacking. OBJECTIVE: The objective is to develop and validate a simplified version of the VES as a patient-reported outcome measure (PROM). METHODS: After extensive pilot testing, patients were asked to score their vitiligo extent twice with an interval of 2 weeks using the Self Assessment Vitiligo Extent Score (SA-VES). The scores were compared with the physicians' evaluation (VES). RESULTS: The SA-VES demonstrated very good test-retest reliability (intraclass correlation = 0.948, 95% confidence interval [CI]: 0.911-0.970) that was not affected by age, skin type, or vitiligo distribution pattern. According to patients, this evaluation method was easy to use (22% very easy; 49% easy; 29% normal) and required <5 minutes in the majority of patients (73%, <5 minutes; 24%, 5-10 minutes; 2%, 10-15 minutes). Comparison of the SA-VES and the VES demonstrated excellent correlation (r = 0.986, P <.001). LIMITATIONS: Few patients had a dark skin type. CONCLUSION: The results demonstrate excellent reliability of the SA-VES and excellent correlation with its investigator-reported counterpart (VES). This patient-oriented evaluation method provides a useful tool for the assessment of vitiligo extent.

What Do People Know and Believe about Vitamin D?

People have been exposed to a lot of information regarding vitamin D, with evidence suggesting that vitamin D may be involved in numerous health conditions, subsequently creating concerns about vitamin D insufficiency. As a result, what do people really know or believe about this topic? In this cross-sectional study, we assessed vitamin D-related knowledge and beliefs in 59,273 French adults (NutriNet-Santé cohort) using a specific questionnaire. Answers to this questionnaire were weighted according to the French sociodemographic distribution and compared across individual characteristics, using χ²-tests. Physicians and media were identified as key information providers. Participants did not always accurately cite vitamin D sources (e.g., 72% only for sun exposure, fatty fish: 61%) or established health effects (e.g., bone health: 62%-78%). Conversely, they mentioned incorrect sources and health effects for which there is no consensus yet (e.g., skin cancer). These findings were modulated by age/generational and socioeconomic factors. A strong inconsistency was also observed between participants' true vitamin D status (plasma 25-hydroxyvitamin D concentration) and their opinion about it. This study, the first in Europe with such a large sample, stresses the need for simple and up-to-date supports of communication for the public and healthcare professionals regarding sources and health effects of vitamin D.

Melanoma-associated leukoderma and vitiligo cannot be differentiated based on blinded assessment by experts in the field.

BACKGROUND: Melanoma-associated leukoderma (MAL) is a depigmenting disorder that can occur spontaneously in patients with melanoma. The differences in clinical presentation between MAL and vitiligo are not well defined. This may lead to misdiagnosing MAL as vitiligo, resulting in delayed detection of melanoma. OBJECTIVE: The objective of this study was to assess whether experts in the field can distinguish between MAL and vitiligo, and to assess if discriminative features can be identified. METHODS: We designed an image comparison study in which 4 experts in the field blindly assessed photographs followed by medical history of 11 patients with MAL and 33 with vitiligo. RESULTS: The assessors misdiagnosed 72.7% of MAL cases and marked 80.0% of them as typical vitiligo. The median age at onset of the leukoderma was higher (55 years, P = .001) in MAL. No discriminative features were found. LIMITATIONS: Sampling bias because of inclusion in tertiary referral center is a limitation. CONCLUSION: The clinical presentation of leukoderma in patients with melanoma resembles that of vitiligo. We propose "melanoma-associated vitiligo" as the more appropriate term for leukoderma in patients with melanoma. Clinicians should be aware that depigmentation in vitiligo can also be caused by melanoma-associated vitiligo and a total body inspection should be performed.

The Vitiligo Impact Patient Scale (VIPs): Development and Validation of a Vitiligo Burden Assessment Tool.

Vitiligo has a major impact on health-related quality of life. Although a few vitiligo-specific quality of life instruments exist, there is no specific vitiligo burden tool. We developed and validated a specific vitiligo burden tool according to skin phototype. In total, 301 patients completed 35 items of the Vitiligo Impact Patient scale, of whom 235 were of skin phototype I to III and 66 of phototype IV to VI. The dimensionality of the items was evaluated using factor analyses, with results suggesting three factors in fair- and dark-skinned patients ("Psychological effects on daily life," "Relationships and Sexuality," and "Economic Constraints, Care & Management of Disease"). Unidimensionality was confirmed by higher order factor analysis. Cronbach's α were high-and intradimensional coherences all demonstrated good reliability (α > 0.8). The final instrument consists of 29 items (19 items common to all patients, 3 specific to fair skin, and 7 to dark skin). The test-retest reliability demonstrated very good reproducibility. The intraclass correlation of each dimension was greater than 0.90 for each population. External validity was confirmed by the correlation coefficients and Bland and Altman plots of the Vitiligo Impact Patient scale-Fair Skin and Vitiligo Impact Patient scale-Dark Skin versus the Short-Form-12, PVC Metra, Body Image States Scale, and Daily Life Quality Index assessment tools.

Burden of inherited ichthyosis: a French national survey.

Moderate to severe ichthyosis is known to have a significant impact on quality of life. A French national survey was performed to describe in more detail how ichthyosis impacts the patients' lives. A questionnaire specifically dedicated to ichthyosis was distributed to patients followed in hospital expert centres or members of the French association of patients. A total of 241 questionnaires were completed and returned (response ratio: 29% for children and 71% for adults). A negative impact of ichthyosis was obvious in terms of domestic life (skin care, housework, clothing, etc.), educational/professional lives (rejections by other children, workplace discrimination, absenteeism, etc) and for leisures/sports activities. The patient's economical resources were also heavily impacted by ichthyosis with important out-of-pocket expenses.

Atopic Dermatitis Burden Scale for Adults: Development and Validation of a New Assessment Tool.

Atopic dermatitis (AD) occurs in approximately 2-3% of adults. The aim of this study was to develop and validate the self-administered Atopic Dermatitis Burden Scale for Adults (ABS-A). Patients were enrolled consecutively from those attending the Station Thermale Avène for a diagnosis of AD. ABS-A was developed using standard methodology, and consisted of 3 phases: exploratory, development, and validation. Internal consistency (Cronbach's α), concurrent validity (Spearman's correlation between ABS-A, SF-12 and Dermatology Life Quality Index [DLQI)]), and discriminant validity, were analysed. A total of 128 adults (68.8% females) completed the ABS-A, consisting of 18 items grouped into 4 domains. ABS-A showed good internal coherence (Cronbach's α, 0.89) and was correlated with both SF-12 components [r = -0.36, p < 0.0001 (Physical); r = -0.52, p < 0.0001 (Mental)] and DLQI (r = 0.78; p < 0.0001). The ABS-A score varied significantly according to AD severity. To our knowledge, ABS-A is the first specific tool for assessing AD burden in adult patients.

Assessment of tyrosinase variants and skin cancer risk in a large cohort of French subjects.

BACKGROUND: Tyrosinase (TYR) is a key pigmentation gene that is highly polymorphic and responsible for the most common form of autosomal recessive albinism, OCA1. OBJECTIVE: To assess the role of frequent and rare TYR variants in predisposition to skin cancer (SK) in the French population. METHODS: We genotyped a frequent TYR variant (p.R402Q) in 1273 patients {1047 cutaneous melanoma (CM) and 226 basal cell carcinoma (BCC)} and 925 controls, and the full coding region of TYR was sequenced in 287 patients suspected of genetic predisposition to SK (familial and/or multiple SK and/or onset before 40 years) and 187 controls. RESULTS: The homozygous p.R402Q variant was significantly associated with SK risk (P value=0.008; OR=1.57), and was mostly associated with multiple CM risk (P value=0.021; OR=2.50) and familial CM risk (P value=0.022; OR=2.16). In addition, 19 rare TYR variants, mainly albinism mutations, were identified in 15 patients and 8 controls. Among these, 3 clearly deleterious mutations (1 non-sense and 2 affecting mRNA splicing) were identified in 3 patients, one of which was homozygous. CONCLUSION: Our data confirmed the association of TYR p.R402Q with SK risk in the French population, and support that rare deleterious TYR variants may also play a role in multi-factorial genetic predisposition to SK. These results should be confirmed by replications studies.