There may be no way to know the answer to this question. A recent study in Quebec, Canada, looked at the differences between employed women and homemakers. All the women had seen a doctor for low back pain.
Pain levels and function were measured four to six weeks after the doctor visit. All women were rechecked one year and two years later. Pain levels and number of disability days were the same for both groups.
It may be that unhealthy women tend to stay home. Those who have good health can get a job outside the home. This is called the healthy worker effect.