Self-report is the most commonly used adherence measure in both clinical and research settings because it is has low staff and respondent burden, and is inexpensive, flexible, and takes very little time. In clinical settings, self-report allows for a discussion of reasons for missed doses and potential solutions. The validity of self-report for antiretroviral adherence has been demonstrated in two recent reviews. A systematic review of 77 studies employing various self-report adherence measures reported that self-reported adherence was significantly correlated with HIV viral load in 84% of recall periods (4
). In a meta-analysis of 65 studies, despite significant heterogeneity in point estimates, the odds of having detectable HIV viral load was more than double in non-adherent patients compared to adherent patients (ORadj
=2.31, 95%CI=1.99 - 2.68) (5
Because of its numerous advantages, self-report is the most likely candidate for widespread use. However, there are several unresolved measurement issues regarding the psychometric characteristics of specific self-report items. Currently, numerous different adherence questions are used in clinical and research settings (4
). Most commonly, respondents are asked to report the number of doses they missed during a specified recall period or to estimate their overall percent adherence on a visual analog scale. Response tasks may also include qualitative estimates of overall adherence, reporting the number of days of perfect adherence in the prior week, recalling when the respondent last missed a dose, or determining the number (or proportion) of doses (or pills) missed (or taken) over a specified recall period. Substantial variation also exists in the relevant time frame, with recall periods including the past one, three, seven, or thirty days (4
). Response options may be Likert (6
) or visual analog scales (9
), and may be close-ended or open-ended. Some self-report measures consist of a single item, some are scales (12
), and some questions assist the respondent with visual aids or anchors. Data suggests poor agreement between different self-report adherence measures (10
). The range of self-report items used makes it difficult to compare results even among studies that all use self-report.
Another important unresolved methodological issue is how to mitigate the “ceiling effect,” or the tendency of self-reported adherence to be positively skewed. This bias increases the risk of patient misclassification and presents analytic challenges for investigators. Though often attributed to social desirability bias, the ceiling effect may be influenced by other factors such as question misinterpretation and poor recall (16
). For example, if a respondent is asked about number of missed pills but answers about the number of missed doses, adherence would be overestimated. Alternatively, because recall for events remembered is more accurate than for those forgotten (18
), patients may overestimate adherence due to differential recall. Because of the ceiling effect, self-report is often considered specific but not sensitive for diagnosing poor adherence (19
). However, some data suggest that self-reported adherence is inaccurate even among patients who report missing doses, and should therefore not be considered 100% specific for poor adherence (20
Several interview techniques may lessen the ceiling effect associated with self-reported adherence. It has become standard practice in clinical and research settings to introduce adherence questions with a statement that normalizes non-adherence by acknowledging the challenges of regular medication taking (21
). Some research suggests that patients and research participants may be more candid about their behavior when answering questions anonymously on a computer screen instead of in a face-to-face interview. Computer Assisted Self-Interview (CASI), which can include an audio component that eliminates literacy requirements, has been shown to increase reporting of numerous socially undesirable or stigmatizing behaviors in various populations (22
). Though CASI has be shown to be feasible in clinical settings (25
) and has become popular for measuring adherence in research settings, data examining the effects of this method on response rates or validity is lacking.
Two potential directions for future investigation may provide insight into ways to improve self-reported adherence. The first is cognitive interviewing, which was developed through collaboration between survey methodologists and cognitive psychologists. Cognitive interviewing is the study of how targeted audiences interpret, mentally process, and form responses to survey questions, with an emphasis on potential biases in this complex process (26
). In one study, cognitive interviews of adherence questions revealed that complex recall tasks and estimation of percentages were particularly challenging without the help of a trained interviewer. Since the investigators were planning to use a self-administered survey, the results of the cognitive interviews prompted them to change their questions to enable respondents to complete them on their own (28
). With an enhanced understanding of how respondents interpret adherence questions and what strategies they use to recall information and formulate answers, better self-report questions that minimize response error can be developed and tested.
A second potential method for improving self-reported adherence uses Item Response Theory to combine information from multiple questions, or items, that measure a latent trait. Unlike Classical Measurement Theory, which relies on the demonstration of reliability and validity, does not separate sources of error, and combines items to create a composite “score,” Item Response Theory enhances precision by finely differentiating sources of error and evaluating each item's relationship to the construct of interest (29
). Because of its advantages over Classical Measurement Theory, Item Response Theory is increasingly being applied in health research (29
Before the adherence research community can converge on evidence-based standards for self-reported adherence, rigorous survey development and testing are needed. Fortunately, empirical testing of adherence questions is beginning to advance the science of self-reported adherence (6