Assessment of Family-Reported Medication Adherence
See Table I for the sample demographic characteristics and descriptive adherence data.
Adherence level indicated by parent-report (median = 98.8%) was significantly higher than EM adherence (median = 91.7%; Wilcoxon-signed ranks test Z = −3.76, p < .001). Parent-report and EM adherence were positively correlated (Spearman's rho = .64, p < .001, n = 40).
See Table II for sensitivity and specificity calculations for all planned and exploratory adherence cut-points. The 90% cut-point provided the highest sensitivity and specificity (ROC analysis AUC = .69, p < .05), 80% (AUC = .67, p = .08), 70% (AUC = .50, p = 1.0), 60% (AUC = .50, p = 1.0) and 50% cut-points (AUC = .50, p = 1.0).
The exploratory cut-point analysis (i.e., 85%; AUC = .66, p = .10) further supported the finding that the 90% cut-point provided the highest sensitivity and specificity. Exploratory analyses (i.e., t-tests) were conducted to examine the difference between parent-reported and EM adherence for people above and below the 90% cut-point. The results indicated that the difference between parent-reported and EM adherence was significantly greater for patients below the 90% cut-point (mean difference = 17%, SD = 19%) as opposed to patients above the 90% cut-point for adherence (mean difference = 1%, SD = 5%; t = 3.8, p = .001).
The first method of analysis yielded a regression equation for correcting parent-reported adherence: Corrected adherence (%) = −12.46 + [1.04 × (parent-reported adherence %)]. After this regression equation was applied to parent-reported adherence levels, a one-sample t-test comparing the difference between EM adherence and the regression-based corrected adherence levels to a test value of 0 was non-significant (t = −.09, p > .05), indicating that the regression-based adjustment reliably corrected parent-reported adherence based on the objective, EM adherence.
The second, exploratory method of analysis, which involved calculating a correction factor based on the first half of the sample, yielded a correction factor of .924 (SD = .14) [i.e., corrected adherence (%) = .924 × (parent-reported adherence %)]. After applying this correction factor to the second half of the sample, a one-sample t-test comparing the difference between the corrected parent-reported adherence levels and EM adherence levels to a test value of 0 was non-significant (t = −.92, p > .05), indicating that the correction factor reliably adjusted the parent-reported adherence levels based on the objective, EM adherence.
The mean difference between the corrected adherence values (i.e., Method 2 corrected value − Method 1 corrected value) obtained by the two correction methods was 1.59% (SD = 1.03%).
Results
See Table I for the sample demographic characteristics and descriptive adherence data.
Comparison of Adherence by Method of Assessment
Adherence level indicated by parent-report (median = 98.8%) was significantly higher than EM adherence (median = 91.7%; Wilcoxon-signed ranks test Z = −3.76, p < .001). Parent-report and EM adherence were positively correlated (Spearman's rho = .64, p < .001, n = 40).
Sensitivity, Specificity, and ROC Analyses
See Table II for sensitivity and specificity calculations for all planned and exploratory adherence cut-points. The 90% cut-point provided the highest sensitivity and specificity (ROC analysis AUC = .69, p < .05), 80% (AUC = .67, p = .08), 70% (AUC = .50, p = 1.0), 60% (AUC = .50, p = 1.0) and 50% cut-points (AUC = .50, p = 1.0).
The exploratory cut-point analysis (i.e., 85%; AUC = .66, p = .10) further supported the finding that the 90% cut-point provided the highest sensitivity and specificity. Exploratory analyses (i.e., t-tests) were conducted to examine the difference between parent-reported and EM adherence for people above and below the 90% cut-point. The results indicated that the difference between parent-reported and EM adherence was significantly greater for patients below the 90% cut-point (mean difference = 17%, SD = 19%) as opposed to patients above the 90% cut-point for adherence (mean difference = 1%, SD = 5%; t = 3.8, p = .001).
Correction Factor
The first method of analysis yielded a regression equation for correcting parent-reported adherence: Corrected adherence (%) = −12.46 + [1.04 × (parent-reported adherence %)]. After this regression equation was applied to parent-reported adherence levels, a one-sample t-test comparing the difference between EM adherence and the regression-based corrected adherence levels to a test value of 0 was non-significant (t = −.09, p > .05), indicating that the regression-based adjustment reliably corrected parent-reported adherence based on the objective, EM adherence.
The second, exploratory method of analysis, which involved calculating a correction factor based on the first half of the sample, yielded a correction factor of .924 (SD = .14) [i.e., corrected adherence (%) = .924 × (parent-reported adherence %)]. After applying this correction factor to the second half of the sample, a one-sample t-test comparing the difference between the corrected parent-reported adherence levels and EM adherence levels to a test value of 0 was non-significant (t = −.92, p > .05), indicating that the correction factor reliably adjusted the parent-reported adherence levels based on the objective, EM adherence.
The mean difference between the corrected adherence values (i.e., Method 2 corrected value − Method 1 corrected value) obtained by the two correction methods was 1.59% (SD = 1.03%).