Methods: Qualitative and quantitative content and face validities were applied. In the qualitative phase of content validity, the homeless women evaluated wording, grammar, item allocation, and scaling of the questionnaire. In the quantitative phase, the content validity index (CVI) and the content validity ratio (CVR) were calculated. In the qualitative phase of face validity, 40 homeless women were asked to evaluate the questionnaire and indicate if they felt difficulty or ambiguity in the questionnaire. In the quantitative phase, the impact score was calculated. The Kuder-Richardson correlation and test-retest reliability were calculated to assess the internal consistency and stability of the questionnaire. 

Findings: The ICC for the questionnaire was achieved at 0.86 (good to excellent), lending support to the stability of the questionnaire. The Kuder-Richardson correlation of the questionnaire was 0.85 (good to excellent). Impact scores of the items ranged from 1.2 to 5. In the quantitative content validity, items with CVR and CVI less than 0.59 and 0.79, respectively, were omitted; overall, 10 items were deleted in this part of the validity.

Conclusion: This study suggests that PSTIQ is a valid and reliable. It could be used to design appropriate interventions to prevent (STIs) in high risk groups, especially homeless women. 

Keywords: Validity and reliability, Sexually transmitted infections, Homeless women