We trust the scientific method to give us reliable knowledge. Nevertheless, research should never be taken at face value. There are many ways a study can be biased and it is extremely important to be able to interpret the results of a study critically. The issue of validity is of particular importance. Are the results valid or is the study flawed to the extent that the conclusions are not supported by the data? Internal validity refers to the integrity of the study methods. Is there a fatal flaw that is intrinsic to the design of the design? For example, a study comparing the effectiveness of two drugs used one drug that had passed its expiration date. In this case, drug B may be less effective than drug A simply because it passed its expiration date. External validity refers to the extent to which the results can be applied to a larger population. A study of attitudes toward religion that only includes atheists will have limited external validity. It may be an accurate measure of the subjects’ religious beliefs but the study would not tell us much about non-atheists. In general, internal validity is more important than external validity.