ABSTRACT
Researchers often manipulate independent variables in their research and observe the consequences of such manipulations on dependent variables. In so doing, they have to take account of other aspects of the research which could interfere with the results that they have obtained. In addition, if they wish their findings to be generalisable, they have to consider the external validity of their research designs. If researchers want to investigate the causal relationship between the independent and dependent variables in their research they have to consider the internal validity of their research designs. Researchers who are testing an explicit hypothesis, statistically, have to formulate it as an Alternative Hypothesis and propose a Null Hypothesis to match it. The research will then provide evidence which will allow the researchers to choose between the hypotheses.
