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. Author manuscript; available in PMC: 2015 Aug 1.
Published in final edited form as: Pharmacoepidemiol Drug Saf. 2014 Mar 24;23(8):830–838. doi: 10.1002/pds.3611

Table 2.

Strength of Instrumental Variables Based on Nursing Home Prescribing Preference in Predicting Psychotropic Medication Use for Individual Nursing Home Residents

Unadjusted Adjusted(a)
Risk Difference(b) 95% CI Semi-Partial R2 Risk Difference(c) 95% CI Semi-Partial R2
Antidepressants versus Atypical APMs(d)
 IV1: Median groups (lowest vs. highest quantile) 0.325 0.306, 0.343 0.107 0.223 0.215, 0.231 0.057
 IV2: Tertile groups (lowest vs. highest quantile) 0.385 0.364, 0.406 0.150 0.279 0.269, 0.288 0.085
 IV3: Quartile groups (lowest vs. highest quantile) 0.397 0.374, 0.421 0.161 0.309 0.299, 0.319 0.103
Antidepressants versus Hypnotics
 IV1: Median groups (lowest vs. highest quantile) 0.261 0.251, 0.270 0.068 0.248 0.241, 0.256 0.062
 IV2: Tertile groups (lowest vs. highest quantile) 0.329 0.318, 0.339 0.108 0.316 0.308, 0.324 0.100
 IV3: Quartile groups (lowest vs. highest quantile) 0.370 0.358, 0.382 0.137 0.356 0.347, 0.365 0.128
Atypical APMS versus Hypnotics
 IV1: Median groups (lowest vs. highest quantile) 0.327 0.308, 0.346 0.110 0.226 0.218, 0.234 0.060
 IV2: Tertile groups (lowest vs. highest quantile) 0.392 0.371, 0.413 0.158 0.286 0.278, 0.295 0.091
 IV3: Quartile groups (lowest vs. highest quantile) 0.407 0.384, 0.431 0.173 0.320 0.310, 0.330 0.112
(a)

Adjusted for propensity score including all resident and facility characteristics

(b)

1-stage Model: X = α0 + α1Z + ε, with X=exposure and Z=IV

(c)

1-stage Model: X = α0 + α1Z + α2PS + ε, with X=exposure, Z=IV, and PS=propensity score

(d)

For the antidepressant versus atypical APM comparison, the risk difference represents the probability of being prescribed an antidepressant if residing in a nursing home with a preference for antidepressants (i.e., NH in highest quantile) relative to the probability of being prescribed an antidepressant if residing in a nursing home with a preference for atypical APMs (i.e., NH in lowest quantile) represented by α1 in the Model. The interpretation is similar for the other comparisons.