Table 2.

Outcomes, effects and inference.

Type of outcome		Primary or secondary	Inference
			Was an effect found?
			Yes	No
Declared, registered	Adequately powered	Primary*	Confirmatory ‘Intervention X has an effect on outcome Y’	Confirmatory ‘Intervention X does not have an effect of the magnitude for which the trial was powered on outcome Y’
	Inadequately powered	Secondary	Exploratory ‘Intervention X has an effect on outcome Y, but the magnitude of the estimated effect is likely to be larger than the average population effect’	No conclusion possible
Undeclared, not registered	Adequately powered	Secondary	Exploratory ‘Intervention X may have an effect on outcome Y’	Exploratory ‘Intervention X may not have an effect of the magnitude for which the trial was powered on outcome Y’
	Inadequately powered	Secondary	Exploratory ‘Intervention X may have an effect on outcome Y, but the magnitude of the estimated effect is likely to be larger than the average population effect’	No conclusion possible

*Primary outcomes are those that are relevant based on the intervention intent and programme theory and therefore declared and adequately powered. Secondary outcomes are all other outcomes, including those either undeclared and/or inadequately powered.