Studying people w brain injuries can help researchers to understand how memory is supposed to work normally
But clinical studies aren't perfect
Major limitation is the lack of control of variables
Brain injuries experienced by pp were usually unexpected
The researcher had no way of controlling what happened to the pp before + during the injury
The researcher has no knowledge of the pp's memory before the injury
Without this its difficult to judge exactly how much worse it is afterwards
Lack of control limits what clinical studies can tell us about diff types of LTM