A hypothesis can be defined as an educated guess about the relationship between two or more variables.
The null hypothosis states that there is no relationship between the two variables being studied (one variable does not affect the other).
Validity refers to whether a study measures or examines what it claims to measure or examine.
Face validity refers to the extent to which a measure appears on the surface to measure what it is suppose to measure.
Criterion validity is a way of assessing validity by comparing the results with another measure. For example, we could compare the results of an IQ test with school results. If the other measure is roughly compared at the same time we call this concurrent validity. If the other measure is compared at a much later time we call this predictive validity.
Construct validity is a way of assessing validity by investigating if the measure really is measuring the theoretical construct it is suppose to be. For example, many theories of intelligence see intelligence as comprising a number of different skills and therefore to have construct validity an IQ test would have to test these different skills.
Internal validity is related to what actually happens in a study. In terms of an experiment it refers to whether the independent variable really has had an effect on the dependent variable or whether the dependent variable was caused by some other confounding variable.
External validity refers to whether the findings of a study really can be generalised beyond the present study. We can break external validity down into two types.
Population validity - which refers to the extent to which the findings can be…