Evaluation of Procedure: Strengths: The MRI scans provided the researchers with vast amounts of quantitative data relating to the volume and size of the hippocampus enabling them to carry out statistical analysis such as correlational analysis. The study employed many controls. For example the samples were matched for age, sex and handedness. The pixel counting was carried out by a researcher who was experienced in this technique but ‘blind’ to the participants’ condition. MRI scanning technology does not pose any health risks to the participants and all of the participants gave informed consent. None of the participants should have been negatively affected by their experience.
Weaknesses: It is normally difficult to make conclusions form natural or quasi experiments as any differences found between the two groups (e.g. volume of grey matter) may not have occurred because of the independent variable (taxi driver or non-taxi driver). For example, it could be possible that people with certain brain differences are attracted to certain jobs. However, the researchers carried out a correlational analysis which clearly demonstrated that there was a positive correlation between length of time the participants had been driving taxi cabs and their posterior hippocampul volume. This suggests that length of time taxi driving is associated with grey matter within the hippocampus. Although the task of being scanned in an MRI scanner is hardly ecologically valid it would not be possible for the participants to respond to demand characteristics. An obvious weakness of the sample is that the participants were all male. There may be difference between males and females in terms of spatial memory. We could apply the same argument to left handed people.