Table 5 Moderators of light treatment effect on sleepiness by using subgroup analyses with mixed-effects models.

(a)
Subgroup	k	Hedges’s g	95% CI		p (Z)^a	I²
Subgroup	k	Hedges’s g	Lower	Upper	p (Z)^a	I²
Intensity of light treatment (lux)
Group 1
< 1000	2	0.180	0.078	0.282	< 0.001	0
1000–5000	7	0.632	0.423	0.842	< 0.001	0
> 5000	5	0.482	0.234	0.730	< 0.001	0
Group 2
< 2000	3	0.194	0.093	0.294	< 0.001	0
2000–5000	6	0.625	0.402	0.848	< 0.001	0
> 5000	5	0.482	0.234	0.730	< 0.001	0
Group 3
< 3000	6	0.240	0.146	0.334	< 0.001	0
3000–5000	3	0.764	0.359	1.168	< 0.001	0
> 5000	5	0.482	0.234	0.730	< 0.001	0
Treatment duration (daily hr)
≤ 1	7	0.504	0.312	0.695	< 0.001	0
> 1	7	0.400	0.191	0.608	< 0.001	0
Treatment duration (total hr)
≤ 10	10	0.532	0.361	0.703	< 0.001	0
> 10	4	0.309	0.095	0.523	0.005	27.071
Number of daily treatment sessions (n)
1	11	0.400	0.240	0.560	< 0.001	0
> 1	3	0.535	0.261	0.809	< 0.001	0

(b)
Subgroup	k	Hedges’s g	95% CI		p (Z)^a	I²
Subgroup	k	Hedges’s g	Lower	Upper	p (Z)^a	I²
Timing of treatment
Night time	6	0.427	0.170	0.683	0.001	0
Day time or mixed	9	0.431	0.279	0.583	< 0.001	0
Treatment day
Same day	6	0.575	0.347	0.804	< 0.001	0
Different day	9	0.363	0.203	0.522	< 0.001	0
Type of treatment light
Single type of light	11	0.361	0.228	0.494	< 0.001	0
Mixed type of light	4	0.779	0.401	1.158	< 0.001	0
Control treatment
Active treatment	12	0.511	0.312	0.710	< 0.001	0
No treatment	3	0.330	0.146	0.513	< 0.001	0
Shift work
Night shift	8	0.439	0.195	0.684	< 0.001	0
Rotating shift	7	0.430	0.284	0.576	< 0.001	0
Simulated shift
Yes	6	0.454	0.162	0.746	0.002	0
No	9	0.431	0.290	0.573	< 0.001	0
Timing of measure
Night time	8	0.463	0.225	0.702	< 0.001	0
Day time or mixed	7	0.410	0.252	0.569	< 0.001	0
Research design
Randomized controlled trial	4	0.502	0.185	0.820	0.002	0
Randomized crossover trial	11	0.426	0.257	0.595	< 0.001	0
Data handling
Intention-to-treat	7	0.480	0.310	0.649	< 0.001	0
Per protocol or unknown	8	0.305	0.149	0.461	< 0.001	0

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