In biology, a lot of interesting dependent variables are nominal (e.g., survived/died, got cancer/didn't get cancer, reproduced/didn't reproduce, became diseased/did not become diseased, etc). To regress such a variable on a continuous X variable, we use logistic regression. In this lesson, I show you how logistic regression is done, and how to obtain the function relation prob(outcome a) to X (e.g., chance of surviving as a function of size).