An American pathologist says too many doctors are misdiagnosing shaken baby syndrome.

Dr. John Plunkett, testifying on Thursday for the defence in the case of Gordon Singer, said injuries often can just as easily be caused by a simple fall.

Singer, 28, is being tried for the manslaughter death of two-and-a-half-year-old Cole Thompson, who the Crown alleges was shaken to death.

Plunkett says his research proves small children get the same types of brain injuries by falling from as low as one metre. However, he says most doctors discount his findings because they don't want to admit they may be wrong.

"Somebody said something 30 years ago," Plunkett said, "it made sense; it was a nice theory. People simply kept on repeating it and teaching it, and coming to conclusions with no objective evidence that they were correct at all. And now that there is objective evidence that they've been incorrect, they're fighting it tooth and nail."

Plunkett says he studied the cases of 18 children who died from injuries sustained in relatively minor playground falls.

He hopes when the findings are published in a scientific journal in March, the medical profession might not be so quick to diagnose shaken baby syndrome.