8. 5 Hypothesis and endpoints

Several concepts are essential to understand research.

Study question – the hypothesis

The study hypothesis is the idea or theory that the research aims to either prove or disprove. It is the main study question.

All studies need to start with this question.

For example:

• Is something happening? – i.e. does smoking/diet/exercise affect health? or ‘Do bones get more brittle as we age’?
• Can doing something improve health?
• Is one treatment better than (or as good as) another?

Primary endpoint

Every study also needs a primary endpoint (PE).

This is the main way that the results of a trial will be assessed. The primary endpoint is an essential part of the study design.

• The primary endpoint determines how many people will be needed and how long the study will last. This will always be decided before the first participant is even enrolled.
• It includes deciding exactly what will be measured, how it will be measured and how the results will be analysed.
• The primary endpoint decides what level of evidence is needed to prove or disprove the study question. The choice of endpoints can determine whether the final results will be useful.

For example, with a new drug, the primary endpoint is often the percentage of people who have an undetectable viral load at a certain point. This could be after 8 weeks for an early effect or 48 weeks for a longer effect.

But it could also be the average drop in viral load, or the average increase in CD4 count. Or a direct measure of health such as how many people had better or worse health.

Secondary endpoints

Secondary endpoints look at everything else that is important in the study.

• Safety of a drug, side effects.
• Impact on CD4 count.
• Impact on quality of life.
• Cost-effectiveness of treatment and many other factors.

Community involvement in trial design can help ensure that important secondary endpoints are included when the study is first planned.

Last updated: 1 January 2023.