. 2012 Feb 3;7(2):e31617. doi: 10.1371/journal.pone.0031617

Table 3. Mediation effects of 5-HT on the relation between pack-years smoked and COPD.

	Effect	Estimate	SE	P value
Initial: Pack-years smoked	^aTotal: Pack-years smoked on COPD	0.050	0.011	0.000
Mediator: Serotonin (5-HT)	^bPack-years smoked on 5-HT	0.008	0.003	0.003
Outcome: COPD	^c5-HT on COPD given pack-years smoked	0.024	0.007	0.000
	^dIndirect: Pack-years smoked on COPD through 5-HT	0.483	0.046	0.035
	^eDirect: Pack-years smoked on COPD given 5-HT	0.046	0.014	0.001

Since the level of 5-HT was not normally distributed, a log-transformation was performed in the linear regression model. All analyses were adjusted for age.

SE = standard error.

^a,b,c,e

Regression analyses were performed to calculate parameter estimates.

The estimate is the product of the estimates of b and c. After the estimate and SE of the product were calculated, the Sobel test was performed to assess the significance of the indirect effect.