Empirical data is information gained through direct observation or experiment. This is an advantage because we know the truth of theory or the benefits of treatment through empirical evidence An example of this is testing a drug to see if it reduces anxiety.
This is reflected in empirical data i.e. not affected by the expectations of the researcher. This is an advantage because without objectivity we have no way of being certain that data collected is valid. For example, in Gardner and Gardner's study observers might have judged that Washoe was using real words because they wanted him to succeed. For that reason the Gardner's developed a strict set of criteria to make judgements.
The aim of the scientific method is to test hypotheses by falsifying them. This is an advantage because it is not possible to prove a hypothesis correct but you can prove it wronged i.e. falsify it. For example, one of the issues with Freud's theory of psychoanalysis is the lack of proof. His theory produces claims that are untestable because they are un-falsifiable. His view that all men have repressed homosexual tendencies cannot be disproved. If you do find men who have no homosexual tendencies then it could be argued that the men do have feelings but these are not apparent as they have been repressed.
The ideal form of the scientific method is a lab experiment because it enables researchers to demonstrate casual relationships. The experimental method is the only way to do this- where we vary one factor (the IV) and observe it's effect on the DV. Conditions, such as extraneous variables, must be controlled. This is an advantage because if we can't demonstrate relationships then we can't be sure that... for example, a persons anxiety was reduced by the drug used.
Scientists record their methods and standardise them carefully so the same procedures can be followed in the future. This is an advantage because by replicating a study we can demonstrate validity of any observation or experiment. If the outcome is the same this affirms the truth of the original results. For example, an issue with Milgram's study was ecological validity. This study has been replicated in a lab therefore suggesting that findings are valid, however to gain more validity it would have to be replicated in natural settings.