# Questions tagged [collapsible]

A measure is collapsible when its value for a group is equal to a weighted average of the values for its subgroups or elements.

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### What are the issues with absolute risk reduction/relative risk reduction vs odds ratios in reference to variation over risk factors

The following quote is from this: Any measure that has the potential for summarizing a treatment effect with one constant for all types of patients will be non-collapsible when the outcome is ...
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### Odds Ratios paradox? Pooled OR inconsistent with subgroup ORs

I have two groups (A and B) that each produce ORs of 1.44 and 1.50. However, if I combine the frequencies for the two groups to create a pooled dataset, I get an OR of 1.40. I get that it's not going ...
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### Marginal/Conditional odd ratios - collapsibility

I have fitted a logistic regression model to some individual binary data. I am mostly interested in the causal effect of a particular binary variable (A), and so I estimated the marginal odds ratio ...
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### Is there a mathematical definition of non-collapsibility?

When teaching GLMs, it's commonly taught that the linear and log link are collapsible but that the logit is not. The log link is collapsible because the curves are proportional and the means are ...
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It is known that odds ratios enjoy a certain symmetry. For example, the odds ratio of outcome $Y$ is the inverse of the odds ratio of outcome $\neg Y$. Risk ratios, on the other hand, do not enjoy ...