Translation and linguistic validation were implemented in accordance with the guidelines recommended by the original WISQoL creators [16]. Figure 1 illustrates in detail steps involved in the preparation of the POL-WISQoL questionnaire. Initially, two native Polish-speaking authors experienced in questionnaire validation conducted forward, concept-focused translations. Next, the reconciling meeting involving all authors, overseen by a Polish linguist was held. Derived version was subject to a backward translation performed by a native English speaker. The subsequent comparison of the original and backward translated questionnaires did not reveal any conceptual discrepancies. Before pilot testing POL-WISQoL was assessed with Gunning fog readability index. Words classified as “complex” were revised and paraphrased to enhance comprehension where possible. The pilot study included ten patients and was followed by a debriefing session with the revised version. Apart from small grammatical and punctuation changes no improvements have been made. The POL-WISQoL has been designed with the same format as the original questionnaire. The final version used for the validation of the POL-WISQOL is available at the WISQoL questionnaire creators.

Step by step process for POL-WISQoL preparation

Short Form 36 (SF-36) is a commonly used questionnaire for assessing health-related quality of life in a variety of medical professions [17]. It is a generic measure consisting of 36 questions that evaluate eight distinct aspects of everyday functioning. These include Physical and Social Functioning, Role Limitations due to Physical Health and Emotional Problems, and levels of Energy. Additionally, the questionnaire quantifies Emotional Well-being, Pain, and General Health. All recorded answers are converted into 0-100 scale with total and domain scores being mean values of particular items.

WISQoL is the only disease-specific tool designed to evaluate the functional and symptomatic effects of urinary tract stones. It comprises 28 items that are organised into four functional domains: social (D1) and emotional (D2) impact, stone-related symptoms (D3), and vitality (D4). Each item is scored on a 5-point Likert scale, with a maximum score of 140 [10]. In both questionnaires reported QoL improves along with increasing scores.

Patients admitted to the Urology Department of Wroclaw Medical University Hospital for endoscopic treatment of urolithiasis were prospectively recruited for the study. The following treatment methods were utilised: Retrograde Intrarenal Surgery (RIRS), Percutaneous Nephrolithotomy (PNL), Endoscopic Combined Intrarenal Surgery (ECIRS) and Simultaneous Bilateral Endoscopic Surgery (SBES). Only adults who were native Polish speakers and had at least a secondary level education were eligible to participate in this study. Individuals who were illiterate, mentally incapacitated, or diagnosed with conditions preventing informed consent completion were excluded from the study. In addition, a negative answer to 8.1. WISQoL item (“Did or do you currently have stones in your urinary system?”) at the admission to the hospital disqualified individuals from the study. Patients were enrolled in the study regardless of the symptoms presented.

After informed consent completion, patients completed SF-36 and POL-WISQoL questionnaires preoperatively. Of the 180 initially interested in participating in the study, only 157 signed informed consent (enrolment rate 87.2%). However, only 106 out of 157 people completed both questionnaires completely (completion rate 67.5%), with 4 of them marking NO in question 8.1. Successfully enrolled individuals were asked to complete the questionnaires again during a follow-up visit at the outpatient clinic 60 days postoperatively.

Statistical analyses were conducted using Microsoft Excel version 16.86 and IBM SPSS Statistics software, version 27.0.1.0 A significance level was set at p value ≤ 0.05 for all calculations. Additionally, 95% confidence intervals (CIs) for Spearman’s rank correlations were computed using bootstrapping with 1000 iterations per each item tested.

Total and domain scores for POL-WISQoL and SF-36 were calculated in accordance with the scoring guidelines provided by creators of the questionnaires. Depending on type of distribution continuous variables were presented either as means with standard deviations (SD) or as medians with interquartile ranges (IQR). Categorical variables were presented as frequencies with percentages.

Reliability was assessed with internal consistency and test-retest analysis. The former was computed with Cronbach’s α for total and domain scores. Its coefficients were interpreted as unacceptable (< 0.50), poor (0.50–0.60), questionable (0.61–0.70), acceptable (0.71–0.80), good (0.81–0.90), and excellent (> 0.90). Test-retest reliability was evaluated by comparing total and domain scores from initial and 60-day postoperative visits in individuals who reported an unchanged health status. Spearman’s rank correlation was used. Unchanged health status was confirmed by identical answers to items 8.1 and 8.5 in both sets of responses.

The convergent validity of the POL-WISQoL and SF-36 total scores was assessed using Spearman rank correlation. Further evaluation included Spearman’s rho calculation for corresponding domains and items of both questionnaires. Item and inter-domain correlations for POL-WISQOL were also computed. The correlation coefficients were interpreted as follows: poor (≤ 0.20), fair (0.21–0.40), moderate (0.41–0.60), good (0.61–0.80), and excellent (> 0.80). Construct validity was estimated by mean scores comparison between patients who did and did not report currently having stone related symptoms (WISQoL item 8.2). This was established by one-way analysis of variance followed by Tukey’s honest significant difference tests for pairwise comparisons. Readability of the translated version was evaluated using the Gunning fog index.