It's certainly reasonable for a studies across fields with hourly pay or, e.g., including both part-time and full-time (such as the BLS survey cited by the Forbes article), but I'm not sure we can make that assumption for software development - programmer productivity in a given time period is, on its own, somewhat mythically considered to vary by orders of magnitude.
All the academic studies I have seen either adjust for it explicitly or put forward a strong case on why it isn't being included.