8 Internal validity and observational studies

So far, you have learnt to ask a RQ, identify different ways of obtaining data, and design the study.

In this chapter, you will learn how to ensure that the conclusions we can make are logical and sound in observational studies. You will learn to:

• maximise the internal validity of observational studies.
• manage confounding in observational studies.
• explain, identify and manage the carry-over effect in observational studies.
• explain, identify and manage the Hawthorne effect in observational studies.
• explain, identify and manage the observer effect in observational studies.
• explain, identify and manage the placebo effect in observational studies.