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From |
"Ariel Linden, DrPH" <ariel.linden@gmail.com> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
re: st: Standardization necessary for mediation analysis with binary outcome? About binary_mediation ado |

Date |
Thu, 12 Jul 2012 21:28:13 -0400 |

Hi Adam, I won't get long winded here, but when you have categorical mediators and/or outcomes, you need to standardize the given variables in order to get them (Y and M) on the same scale. There are several references I could point you to, but I would start by reading the references below, and more importantly, consider using the user-written command -khb- (findit khb), which these references refer to. Kohler, U., Karlson, K.B., Holm A.: Comparing coefficients of nested nonlinear probability models. The Stata Journal 11, 420-438 (2011) Karlson, K.B., Holm, A.: Decomposing primary and secondary effects: A new decomposition method. Research in Stratification and Social Mobility 29, 221-237 (2011) Karlson, K.B., Holm, A., Breen. R.: Comparing regression coefficients between models using logit and probit: A new method. Sociological Methodology 42, XX (2012) Ariel Date: Wed, 11 Jul 2012 15:30:23 +0800 (SGT) From: Adam Cheung <adam_kalok@yahoo.com.hk> Subject: st: Standardization necessary for mediation analysis with binary outcome? About binary_mediation ado Dear Statalisters, I am estimating an indirect effect of an independent variable X on dependent variable Y through mediator M, in which M is a continuous variable while outcome Y is a binary variable. I do not need to estimate the "proportion of total effect mediated". I only need a coefficient indicating the size of indirect effect for substantive interpretation (such as an unit increase in X increase how much of Y through M). For now, I am using "binary_mediation", written by Phil Ender, to estimate the indirect effect. (https://www.ats.ucla.edu/stat/stata/faq/binary_mediation.htm) In this ado, the indirect effect is "standardized". As some have already pointed out (http://www.nrhpsych.com/mediation/logmed.html), it is not correct to compare the indirect effect with the total effect if the effects are not rescaled. However, since I only want to estimate the size of indirect effect. Is standardization procedure necessary in estimating the indirect effect if the outcome is binary? If I do not read wrongly, some have proposed the product of coefficients method without standardizing the the coefficients in the first place (for example, MacKinnon et al. 2007. The intermediate endpoint effect in logistic and probit regression). And in Preacher and Hayes's program for mediation analysis in other statistical packages, it seems that their programs do not standardize the coefficients before multiplying them (http://www.afhayes.com/public/sobel.pdf). Now, I am totally confused whether standardization is necessary in the context of mediation with dichotmous outcome with product of coefficients approach (in times that proportion of total effect mediation is not the focus). Is there any ado in Stata can do that without standardization (if it is correct to do so). I am aware that it is necessary to rescale the coefficients if we use difference in coefficients method. Since I may want a dichotmous X as well, I am worrying if standardization is problematic for any substantiive interpretation. Thanks. Adam P.S. Strictly speaking, my analysis is more like an "associational" type of analysis. My data do not allow me to estimate average causal mediation effect which is to be estimated by using "medeff"(Imai et al.) * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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