A prospective study was conducted to adolescents who attended the dermatology department of Toledo University Hospital between September 2019 and May 2020. Sampling was consecutive and no probabilistic. The sample size estimated was 5 patients per item but not less than 100 patients in total.17

Inclusion criteria were patients aged 12–19 years, suffering from a diagnosed skin disease, who were able to understand and read Spanish, and were able to give assent or written informed consent. Exclusion criteria included patients with significant co-morbidities that could impact on QoL. All personal information was kept confidential.

T-QoL consists of 18 items scored using an ordinal scale from 0 to 2: Never, Occasionally or Always. The score can be reported as a total score, with minimum of 0 and maximum of 36, or as the scores of the three domains or subscales: Self-image (items 1–8), Physical well-being and future aspirations (items 9–12), and Psychological impact and relationships (items 13–18). Higher scores denote greater impairment of the QoL.

The Spanish validated versions of DLQI,18 designed for adults over 16 years, and CDLQI,19 designed for children between 4 and 16 years, were used as comparators. Both questionnaires consist of 10 items scored 0–3, yielding a maximum score of 30.

We also used a global question (GQ) on self-assessed disease severity on 0–10 scale, with 0 indicating clear skin and 10 most severe diseases.

The adaptation of the T-QoL into Spanish involved two main stages: translation and cultural adaptation, and validation.

For the first one, the guidelines made by the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) Task Force for Translation and Cultural Adaptation were used.20

Differences between test scores, GQ, age and gender groups were studied using the Wilcoxon rank sum test (Mann–Whitney U test) and Cohen's d index. Univariate normality was tested using Kolmogorov–Smirnov test21 and multivariate normality with Mardia test.22

Convergent validity was assessed using Spearman Rank correlation between T-QoL, DLQI, CDLQI and GQ. We hypothesised that convergent validity correlations between the T-QoL and the DLQI and CDLQI would be moderate-to-high and moderate-to-low with the GQ. Effect sizes were interpreted as negligible (r≤0.3), low (r=0.3–0.49), moderate (r=0.5–0.7) and high (r=0.71–0.9) and very high (r>0.9).23

The dimensionality of the test scores was studied by parallel analysis. We performed a confirmatory factor analysis (CFA) on a three-factor correlated model and on a bifactor model with three group factors. The magnitudes of the factor saturation and the item's variance explained by each model (R2) were also analysed.

Cronbach's α and Omega ω were used to assess the internal consistency of the tests. Scores ranged 0.7–0.9 were considered acceptable, and above 0.9 may indicate item redundancy.24–26 We also analysed the Spearman correlation matrix between items, the corrected item-rest of the test correlation, the average correlation inter-items and Guttman's Lambda 6 index (G6).27 Items were considered heterogeneous at G6 values <0.7, consistent close to 0.8, or redundant >0.9.28

Test–retest reliabilities were estimated for the three subscales and the total score using intraclass correlation coefficient (ICC). ICC scores <0.6 were considered insufficient, between 0.60 and 0.74 good, and >0.75 excellent.28 The tests’ temporal stability hypothesis seeks to find similar results between the scores of repeat test participants.

After reviewing the back-translations, it was proposed to change certain expressions whose meaning had different nuances depending on the language (Table 1). The resulting Spanish version of T-QoL was pretested in a pilot group of eight participants with skin disorders. All participants answered the questionnaire with a feasibility of 100% and a response time of less than 3min. In question 1 a synonym to the term “self-conscious” was included for a better understanding. The Spanish version of T-QoL was published on the Cardiff University website in October 2019 (see Supplementary Material): https://www.cardiff.ac.uk/medicine/resources/quality-of-life-questionnaires.

The mean±SD age of the 133 patients was 16.1±1.9 years; 60.2% of patients were >16 years old and 51.1% were females. Diagnoses included acne (65.4%), eczematous dermatosis including psoriasis (10.5%), hyperhidrosis (5.3%), moles (3.8%), tinea versicolor (3.0%) and other (12.0%). A descriptive comparison of T-QoL mean scores at the two time it was administered showed no significant differences (T0: 8.3±6.1; T1: 9.2±6.6; p=0.4). These findings were congruent with the GQ.

No statistical differences were observed between children younger adolescents (12–15.9 years) and older adolescents (16–19 years) at any times when the test was completed (T0: T-QoLchildrenyounger 7.2±5.2; T-QoLadolescentsolder 9.1±6.5; p=0.14; T1: T-QoLchildrenyounger 9.4±6.6; T-QoLadolescentsolder 9.4±6.6; p=0.8). Only in domain 3 scores were higher among those over 16 years (p<0.05, d=−0.362). T-QoL mean score was significantly higher in females than in males globally (T-QoLfemales 10.3±6.4; T-QoLmales 6.3±5.0; p<0.001; d=−0.693), in domains 1 and 3 and in the two moments where the test was administered. We also found gender differences in the GQ, CDLQI and DLQI assessments (GQfemales 4.9±2.6, GQmales 3.7±2.6, p<0.05, d=−0.475; CDLQI/DLQIfemales 4.0±3.6, CDLQI/DLQImales 2.7±3.0, p<0.05, d=−0.385).

The distribution of item scores was also reflected in the mean domain scores with domain 1: Self-image had the highest MS (5.2; range 0–16) followed by domain 3: Psychosocial impact and relationships, (2.1, range 0–12) and domain 2: Physical well-being and future aspirations (1.2, range 0–8).

The Kolmogorov–Smirnov test was significant for the T-QoL total score (D=0.12875; p<0.001), the DLQI/CLQI (D=0.209; p<0.001) and GQ (D=0.107; p=0.020). Therefore, normality cannot be assured for any of the total scores.

The correlations of the T-QoL total scores with the DLQI and CLQI were r=0.75 and r=0.63 with the GQ, suggesting that overall results seem to converge moderately between the different measurement tools.

Reliability indicators reveal pronouncedly high values such as Cronbach's α=0.89, G6=0.91 and Omega ω=0.91. These results show that the items seem to be closely related to each other. In the Spearman correlation matrix between items, questions 1–6 correlate highly with each other (correlation coefficient >0.3). Items 11 and 12 have less significant correlations with other items (Fig. 4). In the item-rest of the test correlation, item 12 is the only with correlation <0.30, being the least correlated with the rest of the test.

Figure 4.

Spearman correlation matrix.

(0,53MB).

For the test–retest, 47 patients (35% of 133) completed the second set of questionnaires after a mean of 12.8 days. ICC was highest for the total T-QoL mean score=0.85 (95% CI=0.77–0.91) followed by domain 1=0.81 (95% CI=0.71–0.88), domain 3=0.80 (95% CI=0.69–0.87) and domain 2=0.75 (95% CI=0.62–0.84).

The total number of patients attending the dermatology consultation was not recorded, nor was the number of adolescents who refused to participate during recruitment. Validation may be hampered by response bias, common to most questionnaire-based studies, although consistency and agreement with other widely used instruments was positively tested.

In the test–retest there was a decrease in sample size, from 133 to 47 (−35%). However, authors decided to proceed with the analysis, as health care conditions drastically changed during the lockdown period (March–June 2020) of the COVID-19 pandemic. This decrease also occurred in the validation of the original version: from 203 to 61 (−30%).16

In conclusion, we have successfully translated, adapted and validated a Spanish language version of the T-QoL for adolescent patients with dermatological diseases. To our knowledge, this is the first version of the T-QoL to be published in a language other than English.

Its implementation in countries and populations belonging to a Spanish language culture will make it possible to expand research horizons and enhance our knowledge of those adolescents with skin diseases, thus contributing to improving their QoL.