TABLE 3.
Instrumental variable analyses of exenatide use
| Specification | Probit | 2SRI (logit outcome) |
|---|---|---|
| Constant | –0.848*** (–1.112–0.583) | 0.239*** (0.141–0.405) |
| # of 30‐day claims | 0.0320 (‐0.0404–0.104) | 1.052 (0.904‐1.223) |
| Age 70–74 | 0.168*** (0.147–0.190) | 1.428*** (1.363–1.496) |
| Age 75–79 | 0.390*** (0.368–0.413) | 2.224*** (2.116–2.337) |
| Age 80–84 | 0.582*** (0.557–0.608) | 3.199*** (3.030–3.377) |
| Age 85 and above | 0.680*** (0.651–0.709) | 3.812*** (3.585–4.052) |
| Male | –0.0567*** (–0.0779–0.0355) | 0.881*** (0.842–0.921) |
| Race, Black | 0.124*** (0.0994–0.148) | 1.273*** (1.213–1.336) |
| Race, Asian | –0.102*** (–0.138–0.0653) | 0.818*** (0.760–0.880) |
| Race, Hispanic | 0.0904*** (0.0651–0.116) | 1.189*** (1.131–1.250) |
| Race, other | –0.0596** (–0.115–0.00394) | 0.879** (0.784–0.985) |
| Dual eligible/received LIS | 0.153*** (0.138–0.169) | 1.350*** (1.309–1.392) |
| Social economic status (zip level): | ||
| Median household income (log) | –0.105*** (‐0.129–0.0814) | 0.816*** (0.778–0.855) |
| High school graduates (%) | ‐=0.215*** (‐0.288–0.142) | 0.662*** (0.572–0.766) |
| Foreign born (%) | 0.142*** (0.0781–0.207) | 1.326*** (1.169–1.504) |
| Owner occupied housing (%) | 0.109*** (0.0543–0.164) | 1.230*** (1.103–1.373) |
| Incidence year of diabetes | ||
| 2003 | 0.00449 (–0.0156–0.0246) | 1.006 (0.967–1.048) |
| 2004 | –0.0207* (–0.0417–0.000398) | 0.961* (0.921–1.002) |
| 2005 | –0.0364*** (–0.0578–0.0150) | 0.926*** (0.886–0.967) |
| 2006 | –0.0533*** (–0.0761–0.0304) | 0.900*** (0.859–0.942) |
| Comorbidities: | ||
| Acute myocardial infarction | –0.0347** (–0.0635–0.00582) | 0.934** (0.882–0.989) |
| Anemia | 0.0792*** (0.0642–0.0943) | 1.180*** (1.144–1.217) |
| Asthma | –0.0264** (–0.0466–0.00609) | 0.948*** (0.910–0.987) |
| Atrial fibrillation | –0.0160* (–0.0350–0.00299) | 0.967* (0.932–1.005) |
| Benign prostate hyperplasia | 0.0293** (0.00552–0.0532) | 1.067*** (1.015–1.122) |
| Cancer, breast | –0.0426*** (–0.0698–0.0154) | 0.918*** (0.869–0.969) |
| Cancer, colorectal | –0.0193 (–0.0535–0.0150) | 0.964 (0.901–1.032) |
| Cancer, endometrial | –0.0486 (–0.111–0.0142) | 0.910 (0.803–1.032) |
| Cancer, lung | –0.0179 (–0.0848–0.0490) | 0.958 (0.838–1.096) |
| Cancer, prostate | –0.00956 (–0.0418–0.0226) | 0.988 (0.924–1.055) |
| Cataracts | 0.00456 (–0.0118–0.0210) | 1.008 (0.975–1.043) |
| Chronic kidney disease | 0.0180** (0.00177–0.0343) | 1.036** (1.003–1.071) |
| Chronic obstructive pulmonary disease | 0.0535*** (0.0375–0.0694) | 1.111*** (1.076–1.147) |
| Congestive heart failure | 0.0462*** (0.0303–0.0620) | 1.095*** (1.061–1.131) |
| Depression | 0.323*** (0.309–0.337) | 1.872*** (1.821–1.926) |
| Glaucoma | 0.00414 (–0.0102–0.0185) | 1.007 (0.979–1.037) |
| Hip fracture | 0.136*** (0.102–0.170) | 1.270*** (1.192–1.353) |
| Hyperlipidemia | –0.0521*** (–0.0760–0.0283) | 0.898*** (0.857–0.942) |
| Hypertension | 0.0435*** (0.0110–0.0759) | 1.099*** (1.027–1.175) |
| Hypothyroidism | 0.00541 (–0.0101–0.0209) | 1.011 (0.980–1.042) |
| Ischemic heart disease | 0.0537*** (0.0381–0.0694) | 1.116*** (1.081–1.152) |
| Osteoporosis | 0.0607*** (0.0449–0.0766) | 1.122*** (1.087–1.158) |
| Rheumatoid arthritis | 0.0476*** (0.0328–0.0624) | 1.104*** (1.071–1.138) |
| Stroke/transient ischemic attack | 0.221*** (0.205–0.237) | 1.520*** (1.474–1.569) |
| Other drug use (%): | ||
| ACE inhibitors | 0.00171 (–0.0126–0.0160) | 1.004 (0.976–1.033) |
| ARBs | –0.0477*** (–0.0642—0.0312) | 0.909*** (0.879–0.939) |
| β2AR agonists | –0.0249** (–0.0455—0.00425) | 0.958** (0.919–0.998) |
| Beta blockers | –0.0482*** (–0.0623—0.0341) | 0.907*** (0.882–0.933) |
| Ca2+ channel blockers | –0.0198*** (–0.0337–0.00589) | 0.957*** (0.931–0.985) |
| DPP‐4 inhibitors | –0.0300* (–0.0636–0.00364) | 0.949 (0.885–1.017) |
| Insulin | 0.0531*** (0.0352–0.0710) | 1.112*** (1.073–1.153) |
| Loop siuretics | –0.0266*** (–0.0434—0.00982) | 0.945*** (0.913–0.978) |
| Metformin | –0.0226*** (–0.0395—0.00559) | 0.956*** (0.923–0.990) |
| Statins | 0.00241 (–0.0120–0.0168) | 1.006 (0.976–1.036) |
| Thiazide diuretics | –0.0460*** (–0.0608–0.0312) | 0.913*** (0.886–0.941) |
| Thiazolidinediones | –0.0335*** (–0.0536–0.0135) | 0.936*** (0.898–0.975) |
| Correlation between disturbances | –0.0574 (–0.1542–0.0394) | – |
| First‐stage residual | – | 0.928 (0.797–1.079) |
Notes: The instrumental variable is a dichotomous variable for patient's primary prescriber prescribing exenatide to someone else. First‐stage F‐test for weak IV F(1, 338 127) = 711.2, P < .0001. Second‐stage t‐test on endogeneity (P = .245 in IV Probit and P = .330 in 2SRI) leads us to fail to reject the null hypothesis of exogeneity; for IV probit, reported correlation is transformed as inverse hyperbolic tangent. Statistical significance is defined at the *10% level, **5% level, and ***1% level.
Abbreviations: 2SRI, two‐stage residual inclusion; ACE, angiotensin‐converting‐enzyme; ARB, angiotensin‐receptor blockers; CI, confidence interval; IV, instrumental variable; LIS, low‐income subsidy; SD, standard deviation.