Test and item information of oral health literacy adult questionnaire: An item response theory study in Himachal Pradesh

Abstract

Context: Item response theory (IRT), is a psychometric measure of trait considering each response positioned on a continuum. Aim: Assessment of item and test information Oral Health Literacy Adults Questionnaire (OHL-AQ) using IRT in the patient visiting the tertiary institution of Himachal Pradesh. Settings and Design: A descriptive cross-sectional study conducted on patients visiting the outpatient department. Methods: Data were obtained from the participant and recorded on a structured schedule using OHL-AQ. Statistical Analysis: The two-assumption essential for IRT are unidimensionality and local independence of items. Unidimensional dichotomous IRT consists of three models and three parameters of difficulty discrimination and guessing. Item response interpretation is based on item characteristic curves, test characteristic curve (TCC), and test information function, and analyses were conducted using the statistical software package STATA version 14. Results: The selection of 3PL model is based on the likelihood ratio test which is higher (χ2 = 133.62, P < 0.0001) than other models (χ2 = 130.41, P < 0.0001). The parameter estimate of pseudo-guessing is 0.02 indicating mild degree of guessing and represent the smallest probability of correct response. The TCC of the study shows that 95% of the randomly selected respondent scored between 3.23 and 14. The median probability of correct response is 8.16 when both difficulty and discrimination parameter is equal. Conclusion: IRT is an estimated probability of a response to a given item. Our study showed that OHL-AQ measures higher levels of OHL more precisely compared to lower levels. The OHL-AQ scale is the precise measure of both high and low levels of OHL.