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. 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.

d

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.