Having fit a logistic regression, I want to do cross-validation.
How can I do this? The usual method of computing predictions and calculating the accuracy doesn't work ... because ... there's nothing to predict. My logistic regression predicts a probability, which I can't compare to anything, as my data is binary 1/0 values.
You could try and predict 1 if the predicted probability is greater than 0.5 and vice-versa, but that only works for trivial cases: in my case, the probabilities are always less than 0.5, so this method would always predict y = 0.