I want to assess the strength of dependence between several risk factors and a dependent variable. The dependent variable is typo 0/1 and the risk factors are eg gender or education category.

I would like to ask what is the difference between the two approaches:

a) I use logistic regression to calculate B, p, OR and 95% CL for each factor separately. For example, a separate analysis for the sexes and a separate analysis for the category of education.

b) I add several factors to one regression analysis. For example, as factors 1 sex, as a factor 2 education category

When I compare the results, I get slightly different OR and much different p. What are the differences?