3.7 The importance of design

Choosing the type of study is only a small part of research design. Planning the data collection process, and actually collecting the data, is still required. Data may be obtained by:

• Using data already available: This is called secondary data.
• Collecting new data: This is called primary data.

Either way, knowing how the data are obtained is important. The design phase is concerned with planning the best way to obtaining the data to ensure the study is internally and externally valid, as far as possible.

External validity, considerations include:

• Sampling: Since we can’t study the whole population, who or what do we study in the population (Chap. 5)? And how many do we need to study? (We need to learn more before we can answer this critical question.)

Internal validity considerations include:

• What else might influence the values of the response variable, apart from the explanatory variable? (Chap. 6)
• Effectiveness: How can the study be designed effectively to maximise internal validity? (Chaps. 7 and 8)
• Data collection: How exactly will the data be collected? (Chap. 10)

Ethical issues must also be considered (Chap. 4), and the limitations of the study understood when the results are interpreted (Chap. 9).

The following short (humourous) video demonstrates the importance of understanding the design!