Once people have health insurance, they are going to be less likely to go to the emergency room for acute health problems and will instead see doctors in their offices and use more preventive care services. Right? Well, it seems logical and there are many supporting anecdotes, but a large randomized trial of Medicaid eligibility in Oregon found that this logic is wrong: After people received Medicaid, they used the emergency room more than they did before.
The value of randomized trials is that they allow comparison of some outcome for one group that receives a treatment to the outcome for another group that doesn’t receive that treatment but otherwise is similar to the treated (“experimental”) group.
Are you convinced? Read chapter 7 on experimental design before you decide that you’ll just go with your gut feelings. And be sure to read “Health Care Myths” in the New York Times:
Researching in a Social World 