Explanatory Analysis of Iranian Students' Nonresponse in PIRLS 2021

The present study aims to identify patterns and factors associated with the occurrence of item nonresponse in the PIRLS 2021, using data from 5,962 fourth-grade students in Iran. Differences in item nonresponse rates were examined from three perspectives: comparative (Iran in comparison with other countries), trends (across different PIRLS cycles), and within-test (based on item characteristics). The results showed that the proportion of item nonresponse among Iranian students was higher than the international average, with particularly pronounced differences in constructed-response items. In addition, the likelihood of blank responses increased with greater text difficulty and higher levels of cognitive complexity in reading processes. Longitudinal analyses revealed that the highest rate of blank responses occurred in 2021, while the lowest was observed in 2011, indicating an overall increasing trend since 2011. Inferential analyses using regression modeling identified response format (constructed-response items) and item difficulty as the most important predictors of item nonresponse, together explaining a substantial proportion of the variance in item nonresponse. Overall, the findings suggest that item nonresponse among Iranian students are more strongly associated with limitations in cognitive ability and the higher mental demands of items.