ABSTRACT
Internal validity concerns observational bias, effect of random variation, outcome variation with the magnitude of the source, strength of relationship between source of exposure and outcome, and time relationship, whereas external validity concerns the applicability of the results to target population. The consistency of the results with those of other studies as well as the plausibility of the results must be specified. In confirmatory studies, strong conclusions can be drawn about the relationships found. Otherwise, it is only exploratory and further studies become necessary. The report should modify the scientific belief by strengthening, weakening or altering existing ones, or creating new ones. For this, the design or analysis should not be flawed. The publications in scientific journals will enable a person's results to be rapidly disseminated throughout the world. Many studies are conducted in order to make policy decision, whether in government or in private industry.
