Evaluate

• The sample size was too small to draw reliable conclusions 


  it is difficult to generalise the results to other people with SZ, as the sample may not have been representative and the participants were all volunteers.
• The sample was potentially culturally biased 


  the sample was drawn from a small area of the USA and consisted mainly of white people. Because there is evidence of different rates of SZ between different ethnic groups and different countries, we should be cautious about making generalisations about the relationship between the brain and SZ.
• The study may lack temporal validity 


  results may become outdated overtime because the study used a different system from diagnosing SZ than the one that is used today.
• Some psychologists would be concerned about the ethics of using scans when we are unclear on their long term consequences 


  this is especially an issue because the participants were scanned just for the sake of research and sometimes after only being administered a placebo.
• The difference in brain activity may have been affected by the haloperidol given to the participants before the other drug 


  although haloperidol was necessary for stabilising the patients, it becomes an extraneous variable that makes it harder to establish cause and effect.