Table 3. Comparison of covariate balance before and after one to one matching across studies, with or without replacement, for each drug group, based upon standardized difference (%) of the logit of propensity score between groups.

			Matching within studies				Matching across studies
Exposure	Before matching		Matching without replacement		Matching with replacement		Matching without replacement		Matching with replacement
	Std dif # (%)	p-value+	Std dif (%)	p-value+	Std dif (%)	p-value	Std dif (%)	p-value+	Std dif (%)	p-value+
Earlier generation FQN	-18.74	<0.0001	-23.58	<0.001	-2.90	<0.001	-14.61	<0.001	0.05	0.022
Later generation FQN	-13.35	<0.0001	-26.53	<0.001	-17.44	<0.001	-12.79	<0.001	0.13	0.14
Macrolide	-26.45	<0.0001	12.48	0.06	9.01	<0.001	-6.37	0.118	-0.03	0.542

^# Std dif = Standardized difference of logit of propensity score in unexposed relative to exposed. FQN = fluoroquinolone.

⁺The differences in propensity score between exposed and unexposed individuals receiving were tested for significance using a paired t-test [34]