It is important to think about validity and reliability when designing your study. This will impact how they will be able to be generalized to the population.
Validity-How likely the measure you are using actually measures your dependent variable.
Reliability-How likely the measure you are using measures the dependent variable consistently (does it measure it each time).
The type of research project you are doing will depict the design you will use:
Within subjects-Used when the researcher is interested in determining whether or not one condition is better than another and is dependent upon having the same participants in both conditions. An example could be determining whether website A is more efficient than website B.
Between subjects-Used when the researcher is interested in determining whether or not one condition is better than another. An example could be determining whether using PowerPoint presentations help students get better grades compared to overhead projections.
Counterbalancing-The practice of randomizing the order of condition for participants (see Tables 1 and 2).
Table 1. Counterbalancing for within subjects design
Table 2. Counterbalancing for between subjects design
Research Designs Section-Manual
Resource:
The following is an additional reading resource that you may find useful:
Research Methods Resource: Heiman, G. (2001). Research Methods in Psychology (3rd ed.). Cengage Learning.