Table 1. Results of multilevel modeling for perceived mental exertion (ME).

	ME0: Intercept Only			ME1: + Level 1 Predictors			ME2: + Level 2 Predictors			ME3: + Random Coefficients			ME4: + Cross-level Interactions
Fixed Componentsa,b
Predictor	ß [S.E.]	df	p	ß [S.E.]	df	p	ß [S.E.]	df	p	ß [S.E.]	df	p	ß [S.E.]	df	p
1. Intercept	0.02 [0.15]	54	.90	-0.23 [0.18]	50	.21	-0.23 [0.17]	50	.20	-0.10 [0.18]	49	.58	-0.19 [0.17]	48	.26
2. Environmental noise in patient rooms	-	-	-	0.28 [0.12]	50	.02	0.27 [0.12]	50	.02	0.27 [0.10]	49	.008	0.30 [0.10]	48	.003
3. Time outside of main work areas	-	-	-	0.87 [0.67]	50	.20	0.73 [0.66]	50	.27	-0.16 [0.81]	49	.84	0.23 [0.76]	48	.76
4. Activity level outside of main work areas	-	-	-	-0.33 [0.20]	50	.11	-0.36 [0.19]	50	.07	-0.30 [0.18]	49	.09	-0.32 [0.17]	48	.08
5. Time outside of main work areas x Activity level outside of main work areas	-	-	-	2.01 [0.84]	50	.02	2.10 [0.81]	50	.01	2.34 [0.75]	49	.003	2.24 [0.73]	48	.004
6. Burstiness of speaking	-	-	-	-	-		-	-	-	0.08 [0.12]	49	.54	0.03 [0.11]	48	.78
7. Patients on an insulin drip	-	-	-	-	-		0.30* [0.12]	33	.01	0.05 [0.12]	33	.68	0.05 [0.11]	33	.64
8. Patients on an insulin drip x Burstiness of speaking	-	-	-	-	-		-	-	-	-	-	-	0.19 [0.07]	48	.01
Random Components
Between-shift variance (σ2e)	0.64 [0.80]			0.46 [0.68]			0.36 [0.60]			0.22 [0.47]			0.17 [0.41]
Within-shift / residual variance (σ2u0)	0.38 [0.62]			0.35 [0.59]			0.35 [0.59]			0.35 [0.59]			0.36 [0.60]
Slope variation (Burstiness of speaking)										0.08 [0.29]			0.02 [0.15]
Variance Modelledc
Level 1: R2Within Shift				0.08			0.05			0.05			0.05
Level 2: R2Between Shift				0.28			0.44			0.66			0.73
Ran. Coef.: R2slope: Burstiness of speaking										0			.75
Model Fit
Deviance (-2 * Log likelihood ratio)d	224.2			210.00			203.40			195.47			190.43
L. Ratio	χ2(1) = 27.30, p < .001			χ2(4) = 14.27, p < .01			χ2(1) = 6.60, p < .05			χ2(3) = 7.93, p = .05			χ2(1) = 5.04, p < .05

^aThere were 89 shift segments nested within 35 shifts.

^bTerms 2–4, and 6 are Level 1 main effects; Term 5 is a Level 1 interaction; Term 7 is a Level 2 main effect; term 8 is a cross-level interaction.

^cProportion of variance explained for Level 1 (within shifts) and Level 2 (between shifts) were calculated relative to ME₀, the model with only a grouping variable; Proportion of slope variation explained was calculated relative to ME₃, the model with random coefficients, but no cross-level interactions.

^d Reduction in model deviance was tested as follows: ME₀ contained only the shift grouping variable and was tested against a model without the grouping variable; ME₁ included Level 1 sensor-based measures and was tested against ME₀; ME₂ included Level 2 task demand fixed effects and was compared to ME₁; ME₃ included random coefficients for Level 1 sensor-based measures and was evaluated relative to ME₂, the model without random coefficients; ME₄ included cross level interactions between Level 1 and Level 2 predictors and was evaluated relative to ME₃.