Table 6.

Univariate predictors of change in pain at endpoint in the placebo population across all studies for continuous variables: younger age, shorter duration of PHN, higher baseline pain score, and longer study duration are significantly associated with a higher placebo response

Variable	DPN				PHN
	n	R-square	βa	P-value	n	R-square	βa	P-value
Age	1,038	0.05462	0.0138	0.0262	476	0.06461	0.0283	0.0007
Duration of NeP	627	0.03579	−0.0006	0.9830	–	–	–	–
Duration of diabetes	685	0.02435	−0.0014	0.8697	–	–	–	–
Duration of DPN	367	0.04232	−0.0068	0.8153	–	–	–	–
Duration of PHN	–	–	–	–	476	0.05975	0.0070	0.0028
Baseline pain score	1,038	0.09065	−0.2895	<0.0001	476	0.04249	−0.0375	0.5039
Study duration	1,038	0.11660	−0.1958	<0.0001	476	0.06967	−0.1226	0.0002

Notes: Not all studies recorded duration of illness; P-values based on Student’s t-test;

^aβ represents the change from baseline to endpoint in daily pain rating scale score associated with a one-unit change in the continuous variable; A negative β implies each unit in the continuous variable is associated with a greater improvement in pain score with placebo.

Abbreviations: DPN, diabetic peripheral neuropathy; NeP, diabetic neuropathic pain; PHN, postherpetic neuralgia.