Table 2.

Descriptive statistics for categories of theory use.

Theory coding scheme categories (category number)	Category description (what the items in each category assess) [19]	Items included	Maximum score	Mean (SD)	Studies scoring ≥1, N
Reference to underpinning theory (C1)	Stated or suggested, rather than demonstrated theoretical base	1, 2, 3	3	1.1 (1.23)	20
Targeting of relevant theoretical constructs (C2)	Whether evidence was provided that a targeted theoretical construct predicted behavior, whether theory or predictors were explicitly used for designing the intervention, and the extent to which the intervention targets particular theory-relevant constructs	2, 5, 6, 7, 8, 9, 10, 11	8	2.0 (2.43)	17
Using theory to select recipients or tailor interventions (C3)	Whether theory was used to select participants likely to benefit from the intervention, or to tailor the intervention to the needs of a particular individual	4, 6	2	0.1 (0.26)	2
Measurement of constructs (C4)	Whether the relevant theory-based constructs or predictors have been measured	12a, 12b	2	0.5 (0.86)	11
Testing of theory: mediation effects (C5)	Whether theoretical constructs are measured, whether the intervention changes the theoretical constructs, and whether these changes explain the effect	12a, 12b, 13, 14a, 14b, 14c, 14d, 15, 16	9	1.6 (2.83)	14
Refining theory (C6)a	Whether the results of evaluating theory-based interventions are used to refine theory	17a, 17b	2	—	—
Total use of theory	—	All items	22	4.4 (5.43)	20

^aNo score >0 for any studies, so not included in the meta-regression analyses.