I just recently started working with logistic regression, and I'm struggling with the interpretation of the results.
Say I have brain disease (BD) as an outcome and gestational age (GE) as an explanatory variable. The OR is 0.99. I have used R to calculate this:
gl1 <- glm(BD~GE, data, family = "binomial")
How do I know what my reference group is in this case? Does the model pick a reference for me? Individuals with disease is explained by 1, and individuals with no disease are 0. The clinical theory is that individuals with a low GE is more likely to get BD.
But this doesn't make sense to me in this case. Every time I Google this issue, I get: "every increase of GE is associated with 0.99 times the odds of BD". But shouldn't it be opposite? That is, every decrease of GE, is associated with 0.99 time the odds of BD?
summary(gl1)and provide the codebook's definition of GE: what units or thresholds are used? Also verify if the OR is on the natural scale or log scale. $\endgroup$