Differential item functioning (DIF) occurs when items in a measure perform in ways that are different for members of a target group when the different performance is not related to the individual’s overall ability to be assessed. DIF may arise for a number of reasons but is often evaluated in order to ensure that tests and measures are fair evaluations of a group’s abilities. Based on observations when administering the test, we developed the hypothesis that some items on the reading comprehension subtest of the Test of Functional Health Literacy (TOFHLA) might be differentially more difficult for older adults and the elderly due to its use of the cloze response format, in which the participant is required to determine what word, when placed in a blank space in a sentence, will ensure that the sentence is intelligible. Others have suggested that the cloze response format may make demands on verbal fluency, an ability that is reduced with the increasing age. Our analyses show that age-related DIF may present in a nearly one-half of reading comprehension items of the TOFHLA. Results of this measure in older persons should be interpreted cautiously. 1. Introduction Health literacy has assumed increasing importance over the past decade as research has continued to accumulate showing that patients’ levels of it have important relations to their health, use of health services, and health outcomes [1, 2]. Health literacy is defined as “… the degree to which individuals have the capacity to obtain, process, and understand basic health information and services needed to make appropriate health decisions [3].” It has been related to a number of variables reflecting patients’ ability to obtain and use information to reach their desired state of health, including use of preventive health services, indices of disease control such as glycosylated hemoglobin in diabetes, risk for hospitalization, and even increased likelihood for death [1, 4]. One especially important finding in health literacy research has been the fact that racial and ethnic minorities and the elderly perform at lower levels on several measures of health literacy compared to the general population [5, 6]. One widely cited study, for example, was the National Assessment of Adult Literacy (NAAL) which included a health literacy scale [5]. The study, based on a nationally representative sample, showed that blacks, Hispanics, and the elderly had lower levels of health literacy on the NAAL health literacy scale. Studies with other measures, including the widely used Test of Functional Health Literacy in
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