Not many years ago, when a child had frequent bouts of sore throat and earache, family doctors recommended removing the child’s tonsils

Statistics Nov 11, 2020

Not many years ago, when a child had frequent bouts of sore throat and earache, family doctors recommended removing the child’s tonsils. Typically, the child’s health improved afterwards. Parents and physicians attributed the improved health to the operation. What threats to internal validity were ignored?