Table 5.

Study size^a of clinical trials and observational studies at the hierarchical level of the data analysis.

	Number of studies	Range of study sizes	Experimental settings	Commercial settings	Unclear settings
Individual	405	9–3,31,592	200	179	26
Group/pen/room	113	2–653	63	45	5
Herd	37	3–1,513	0	37	0

^aStudy size was the number of study subjects included in the analyses.

Some studies measured outcomes at multiple levels.

For some studies some outcomes were measured at the individual level but performance was measured at the pen level.