The English version of the Celiac Dietary Adherence Test (CDAT) will be translated into Polish using the "forward-backwards-forward" translation model, with the author's consent (already obtained by the applicants).

The Polish translation will be performed by two native bilingual speakers of Polish and English. Both translations will be compared and standardised. The Polish version will then be translated into English by two native bilingual speakers of English who are unfamiliar with the original English version. The translation and original will be compared to clarify discrepancies and ensure conceptual equivalence between the versions. The agreed-upon translation will be culturally adapted, if necessary. The items will be reviewed by five experts, and an I-CVI of at least 0.78 will be considered satisfactory content validity.

In the next step, 10 coeliac disease (CD) patients aged 10 years and older and 10 caregivers/parents of CD patients under 10 years of age will be asked to rate the clarity of each statement on a Likert scale [1 = unclear to 5 = very clear]. Questions with a mean score <4.0 will be rephrased and re-evaluated.

Internal consistency analysis using Cronbach's alpha and the mean inter-item correlation (AIC) will be used to assess reliability. Convergent validity will be assessed by comparing scale scores with serological marker levels. Confirmatory factor analysis (CFA) will be conducted, taking into account the SRMR fit index.

Inclusion Criteria:

• diagnosis of coeliac disease (CD) according to the European Society of Pediatric Gastroenterology and Nutrition (ESPGHAN) criteria,
• age from 2 to 18 years of age,
• consent from legal guardians (and the child in case of patients ≥16 years of age) to participate in the study.

Exclusion Criteria:

• whose legal guardians did not consent to participate in the study,
• who did not consent to participate in the study (applies to patients ≥ 16 years of age).

Polish children with CD.