Regression

Fifteen ways regression output gets misread, with the symptom, what it actually means, and how to check. Every one came from a real model.

Alone it reads -0.0054. With seven other predictors, +0.0154. Both significant. Why hunting for the guilty variable is the wrong instinct.

The smoker coefficient is $24,330. That does not mean quitting saves anyone $24,330, and no amount of significance will make it mean that.

Ridge, lasso and elastic net returned identical test error, to the last digit. The reason is a mistake hiding in a workflow you have copied.

Your model says 1.60. That cannot be a probability. Four things that go wrong reading logistic output, and none of them throw an error.