𝟲. 𝗛𝗜𝗚𝗛 𝗘𝗫𝗧𝗘𝗥𝗡𝗔𝗟 𝗩𝗔𝗟𝗜𝗗𝗜𝗧𝗬:
One strength of Bahrick et al.'s study is that it has high external validity.
Real life meaningful memories were studied. When studies of LTM have been conducted with meaningless pictures, recall rates were lower (Shepard, 1967). The downside of real-life research is that confounding variables are not controlled, e.g. participants may have looked at their yearbook photos and rehearsed their memory over the years.
However, this ultimately suggests that Bahrick et al.'s findings reflect a more 'real' estimate of the duration of the LTM.