TABLE 4.

Results of meta‐regressions in the meta‐analyses of correlation coefficients

	Moderator	k cohorts	% Between‐study heterogeneity explained	Estimate (slope)	95% CI	Q m	P‐value
HairF versus BMI	Mean age	120	0.3	0.0006	−0.0005; 0.0017	1.32	0.25
	Mean BMI	113	0.7	0.0003	−0.0050; 0.0057	0.01	0.90
	Adults only	84	0.7	−0.0082	−0.0180; 0.0016	2.70	0.10
	Mean HairF	115	0.002	0.0000	−0.0002; 0.0003	0.10	0.76
	LC–MS	44	2.1	0.0008	−0.0042; 0.0057	0.09	0.76
	CLIA	23	7.4	−0.0025	−0.0092; 0.0041	0.55	0.46
	ELISA	47	0.03	0.0000	−0.0003; 0.0003	0.02	0.88
	% obesity	57	11.9	−0.0029	−0.0049; −0.0010	8.95	0.0028
	% males	122	2.5	0.0003	−0.0006; 0.0011	0.38	0.54
HairF versus BMI SDS	Mean age	11	11.0	0.0127	−0.0091; 0.0344	1.30	0.25
	% males	10	18.6	0.0037	−0.0012; 0.0087	2.18	0.14
	Mean BMI SDS	10	86.4	−0.2108	−0.3408; −0.0807	10.09	0.0015
	Mean HairF	10	1.03	−0.0006	−0.0040; 0.0028	0.12	0.73
HairF versus WC	Mean age	23	21.9	0.0011	−0.0007; 0.0028	1.46	0.23
	Mean BMI	20	9.3	0.0013	−0.0081; 0.0106	0.07	0.79
	Adults only	17	18.3	−0.0080	−0.0267; 0.0108	0.69	0.41
	Mean HairF	21	0.002	0.0003	−0.0006; 0.0012	0.46	0.50
	% obesity	16	0.03	−0.0002	−0.0030; 0.0027	0.02	0.89
	% males	23	39.5	0.0022	0.0010; 0.0033	14.29	0.0002
HairF versus WHR	Mean age	15	10.7	0.0024	−0.0006; 0.0055	2.10	0.12
	Mean BMI	12	13.3	−0.0120	−0.0315; 0.0074	1.47	0.23
	Adults only	10	54.4	−0.0170	−0.0377; 0.0037	2.59	0.11
	Mean HairF	14	4.0	0.0014	−0.0020; 0.0047	0.65	0.42
	LC–MS	11	25.2	0.0056	−0.0013; 0.0126	2.53	0.11
	% males	15	28.7	0.0011	0.0001; 0.0021	5.07	0.02
HairE versus BMI	Mean age	15	27.9	0.0016	−0.0004; 0.0035	2.56	0.11
	Mean BMI	12	47.2	0.0096	−0.0006; 0.0197	3.41	0.07
	Mean HairE	13	65.2	0.0046	0.0025; 0.0068	17.96	<.0001
	% males	15	12.2	0.0010	−0.0010; 0.0030	0.99	0.32

Note: Meta‐regressions were only performed when data of at least 10 cohorts were available. Bold text indicates statistically significant effect (P‐value < 0.05).

Abbreviations: CI, confidence interval; Q_m, Cochrane's Q for the moderator; HairF, hair cortisol; SDS, standard deviation score; WC, waist circumference; WHR, waist‐to‐hip ratio; LC–MS, liquid chromatography‐(tandem) mass spectrometry; ELISA, enzyme‐linked immunosorbent assay; CLIA, chemiluminescent immunoassay; NA, not available or not applicable.