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. 2017 Nov 20;7(11):e015640. doi: 10.1136/bmjopen-2016-015640

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The biases with the effects of E→M₁ (red), M₁→M₂ (blue) and M₂→D (black) increasing, respectively. Comparison of the bias of different effects in three adjustment models: (A) adjustment for M₁, (B) adjustment for M₂ and (C) adjustment for M₁ and M₂. The OR of target effect (eg, E→M₁) from 1 to 10 given the effect of M₁→M₂ fixed ln8 and other effects fixed ln2 (colour figure online).