Managed Care - February 2009 - (Page 43) TABLE 4 Multivariate regression analysis of HEDIS score with analog insulin, human insulin, and brand oral prescription share; plan enrollment; and plan location Drug class, enrollment, location Analog insulin share Human insulin share OAD share (brand ) Small enrollment Medium enrollment Large enrollment East north central South Atlantic/Central Mountain Pacific Correlation with HEDIS 2005 (N = 194)* −0.263 0.148 0.429 −0.010 −0.002 −0.013 −0.007 0.035 0.040 0.011 Correlation with HEDIS 2006 (N = 211)* −0.288 0.298 0.491 −0.003 −0.011 −0.006 −0.006 0.032 0.036 0.002 P value† 0.02 0.48 0.01 0.50 0.91 0.47 0.65 0.02 0.02 0.67 P value† 0.01 0.15 0.00 0.82 0.39 0.71 0.64 0.01 0.02 0.94 Small enrollment = 100,000 to 249,999; medium enrollment = 250,000 to 749,999; large enrollment ≥750,000 Enrollments under 100,000, northeast and mid-Atlantic used as reference and not included in model *A negative model coefficient indicates a favorable correlation between HbA1c control and prescription share. Model statistics: r2=0.161, p<0.001, F-test (year 2005); r2=0.207, p<0.001, F-test (year 2006). † t test OAD = oral antidiabetic drug ment and location in the multiple regression model increased the unfavorable effect of human insulin with respect to analog insulin. The linear regression with percentage of diabetes prescriptions on the lowest copayment tier as the independent variable showed a small nonsignificant effect (Table 5). For 2005, a higher percentage of prescriptions in the lowest copay tier was associated with a better (lower) HEDIS score. The slope was –11.3, indicating a 1.1 percentage point drop in HEDIS score for a 10-sharepoint increase in prescriptions in the lowest copay tier (p = 0.06). In 2006, this relationship diminished to a slope of –7.4. DISCUSSION These results of this study corroborate those reported in the earlier study (years 2004 and 2005), which used more limited prescription volume information (Weiss 2007). A strong relationship between better (lower) HEDIS scores for HbA1c control and higher analog insulin prescription share was demonstrated by both the univariate and multivariate regression analyses for 2005 and 2006. Human insulin share showed a favorable relationship to HEDIS scores in the univariate analysis in both years but without statistical significance. The multivariate analysis attributed the improvement in HEDIS scores to analog insulin only, with human insulin showing a slight (nonsignificant) unfavorable effect on HEDIS scores in both years. The inclusion of plan enrollment and location in the multiple regression analysis resulted in a further differentiation between analog and human insulin, with human insulin showing a greater unfavorable impact, although still not reaching statistical significance. Both the univariate and multivariate regressions demonstrated an unfavorable relationship between oral product shares and HEDIS scores. The relationship was much more pronounced for the brand oral products, with higher brand oral market shares in health plans associated with statistically sig- TABLE 5 Results of univariate (simple) regression between HEDIS score and percentage of diabetes prescriptions in lowest copayment tier Mean percent of diabetes prescriptions by copayment tier Tier 1 2005 2006 68.4% 70.5% Tier 2 30.7% 28.2% Tier 3 0.9% 1.3% Slope -11.3 -7.4 p-value 0.06 0.18 Percentages are based on prescriptions for products with known copayment tiers FEBRUARY 2009 / MANAGED CARE 43
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