Table 5.

Univariate predictors of change in pain at endpoint in the placebo population across all studies for categorical variables: being female, higher active treatment:placebo ratio, and studies conducted postapproval are significantly associated with a higher placebo response

Variable	DPN			PHN
	n	Mean (SD)a	P-value	n	Mean (SD)a	P-value
Sex			<0.0001			0.0016
Female	466	−1.85 (2.22)		231	−1.12 (1.92)
Male	572	−1.64 (2.11)		245	−0.91 (1.82)
Site recruitmentb			<0.0001			0.0036
≤5	735	−1.65 (2.10)		367	−1.02 (1.87)
6–8	231	−1.99 (2.41)		91	−1.07 (1.90)
9–11	40	−1.63 (1.84)		18	−0.65 (1.69)
≥12	32	−1.99 (1.91)		–	–
Pregabalin approval statusc			<0.0001			0.0028
Preapproval	467	−1.47 (2.11)		361	−0.85 (1.88)
Postapproval	571	−1.95 (2.18)		115	−1.52 (1.75)
Enrollment periodd			<0.0001			0.0136
1st quartile	224	−1.56 (2.15)		46	−0.94 (1.94)
2nd quartile	218	−1.77 (2.29)		129	−0.99 (1.87)
3rd quartile	263	−2.03 (2.18)		136	−0.98 (1.83)
4th quartile	333	−1.60 (2.05)		165	−1.08 (1.90)
Ratio of active:controle			<0.0001			0.0028
1:1	287	−1.26 (1.96)		84	−1.10 (2.03)
≥2:1	751	−1.92 (2.21)		392	−0.99 (1.84)
Sites per study, n			<0.0001			0.0028
10–26	222	−1.55 (2.04)		116	−1.22 (1.96)
27–42	82	−1.18 (1.80)		186	−1.30 (1.79)
43–49	357	−1.88 (2.29)		81	−0.48 (1.65)
50–76	377	−1.82 (2.16)		93	−0.63 (1.95)

Notes: P-value based on Student’s t-test;

^amean change (SD) from baseline in pain score at endpoint in the pooled placebo arms;

^bnumber of patients recruited at each site;

^cpregabalin approval status at the commencement of the study;

^dpoint of patient enrollment into the study relative to full study population;

^eratio of the total number of patients receiving active treatment to patients receiving placebo.

Abbreviations: DPN, diabetic peripheral neuropathy; PHN, postherpetic neuralgia; SD, standard deviation.