If
dependent variable is a proportion (ranging from 0 to 1), then your predicted
values must be a proportion, logically. Therefore we use
logit transformation of dependent. Before we proceed further we need to know
some terms:
- Ogive/ sigmoidal/ flattened S-curve:
It is linear in middle part, but categorical on extremes
- Logit transformation: If your dependent variable is ranging from 0 to 1, e.g. any proportion, then use logit transformation. For Example: If x is dependent then logit transformation is ln(x/(1-x)).
If most of the dependent values are ranging in
middle linear part of the curve (from 0.3 to 0.7), we can use simple OLS
instead of logistic regression. (http://www.theanalysisfactor.com/proportions-as-dependent-variable-in-regression-which-type-of-model/)
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