My dependent binary variable is Turnout in 2010 elections (yes/no) and I'm performing logit analysis using a cross-sectional dataset.

There's a variable though called Past vote in 2005 elections i.e. (Abstain,Conservative,Labout,etc) and, as we expected,its high correlated with Turnout in 2005 and significant in our regression.

Is it right to put it in the model? When we include it the constant term of the logit regression has a p-value of 0.800 and when we exclude it, 0.000.

Cheers