Effects of Adjusting for Instrumental Variables on the Bias and Precision of Propensity Score Weighted Estimators: Analysis Under Complete, Near, and No Positivity Violations

Purpose

To demonstrate that using an instrumental variable (IV) with monotonicity reduces the accuracy of propensity score (PS) weighted estimators for the average treatment effect (ATE).

Methods

Monotonicity in the relationship between a binary IV and a binary treatment variable is an important assumption to identify the ATE for compliers who would only take treatment when encouraged by the IV. We perform theoretical and numerical investigations to study the impact of using the IV that satisfies monotonicity on the PS of treatment in terms of the positivity assumption, which requires that the PS be strictly between 0 and 1, and the accuracy of PS weighted estimators. Two versions of monotonicity that result in one-sided or two-sided noncompliance are considered.

Results

The PS adjusting for the IV always violates the positivity assumption when noncompliance occurs in one direction (one-sided noncompliance) and is more extreme than without the IV under two-sided noncompliance. These results are valid if the probability of being encouraged to get treatment and the compliance score, the probability of being a complier, are strictly between 0 and 1.

Conclusion

Using a binary IV with monotonicity as a covariate for the PS model makes the estimated PSs unnecessarily extreme, reducing the accuracy of the PS weighted estimators.

Behavioral and cardiovascular effects of a single dose of gabapentin or melatonin in cats: a randomized, double-blind, placebo-controlled trial

OBJECTIVES

The aim of this study was to verify whether a single oral dose of gabapentin (100 mg) or melatonin (3 mg) given 60 mins before a cardiac evaluation would reduce anxiety without interfering with heart rate (HR), systemic blood pressure (SBP), electrocardiogram (ECG) and echocardiographic indexes.

METHODS

Seventy-five client-owned healthy cats underwent two sets of cardiac assessments 60 mins apart, randomly divided into gabapentin, melatonin and placebo groups. The interval between treatment and the second ECG and SBP measurement was 60 mins, and 70 mins for echocardiography. A compliance score (CS) classified the behavior, focusing on the ease of handling.

RESULTS

Most variables did not change between the examinations. The placebo group showed more significant changes (SBP, tricuspid annular plane systolic excursion, HR during echocardiography, aortic flow velocity, S' wave from lateral mitral annulus), but they were not considered to be hemodynamically relevant. Gabapentin and melatonin significantly increased the cats' compliance without interfering with cardiac assessment. Eight cats presented with mild sedation, seven after gabapentin and one after melatonin. No major side effects were observed.

CONCLUSIONS AND RELEVANCE

Gabapentin tranquilized the cats when it was given 60 mins prior to ECG and SBP measurement, and 70 mins prior to echocardiography, without interfering with systolic echocardiographic indexes. Melatonin also decreased the CS, but without sedation in most cases. The waiting period may have relaxed the cats in the placebo group, resulting in lower SBP measurements. However, this tranquility did not last as some echocardiographic changes signaled a sympathetic predominance.

Effect of safety education on knowledge of and compliance with road safety signs among commercial motorcyclists in Uyo, Southern Nigeria

OBJECTIVE

Compliance with road safety signs is important in the reduction of motorcycle accidents. The aim of this study was to implement health education intervention and assess its impact on the knowledge of and compliance with road safety signs among commercial motorcyclists in Uyo, Southern Nigeria.

METHOD

This was an intervention study among motorcyclists in Uyo, Southern Nigeria, with a control group from a similar town. The instrument of data collection was a semi-structured interviewer administered questionnaire. Subjects were selected through multistage sampling method. Baseline data on compliance to road safety signs was collected from both groups. Motorcyclists in the intervention group were given education on the importance of compliance to road safety signs. Data was subsequently collected from both groups 3 months post intervention and analysed using the Statistical Package for the Social Sciences version 11.

RESULT

A total of 200 respondents participated in the study, 100 from each group. Following intervention, respondents with good knowledge score increased from 21% at baseline to 82% at 3 months post intervention in the intervention group (p<0.05) and from 19% to 21% in the control group. Compliance score in the intervention group increased from 15% to 70% (p<0.05) and from 12% to 18% in the control group.

CONCLUSION

A significant increase in compliance to road safety signs was recorded among motorcyclists in the intervention group after safety education. All motorcyclists should therefore be given education on road safety signs as this will improve compliance and lead to safer road use among them.