. Author manuscript; available in PMC: 2013 Oct 1.

Published in final edited form as: Chronobiol Int. 2012 Aug 10;29(8):1036–1047. doi: 10.3109/07420528.2012.706766

TABLE 4.

Analysis of covariance of daylength and P10L genotype on sleep onset and chronotype

			F	p	η²	Levene^b
Sleep onset
Additive model	P10L		3.337	.037^*	.029	.552
	Daylength		.816	.367	.004
	P10L × Daylength		3.345	.037^*	.029
		CC vs. TT^a	3.430	.065
		CT vs. TT^a	6.090	.014^*
Recessive model	P10L (TT vs. CT&CC)		4.307	.039^*	.019	.271
	Daylength		2.800	.096	.012
	P10L × Daylength		3.894	.049^*	.017
Chronotype
Additive model	P10L		3.328	.038^*	.029	.719
	Daylength		4.428	.036^*	.020
	P10L × Daylength		3.214	.042^*	.028
		CC vs. TT^a	4.150	.043^*
		CT vs. TT^a	6.260	.013^*
Recessive model	P10L (TT vs. CT&CC)		5.021	.026^*	.022	.468
	Daylength		6.520	.011^*	.029
	P10L × Daylength		4.621	.033^*	.020

Seasonality is the Global Seasonality Scale (GSS) from the Modified Seasonal Pattern Assessment Questionnaire. Partial eta squared (η²) effect size for ANCOVA is estimated to be small = .01, medium = .06, and large = .14 (Cohen, 1988).

In the event of significant interactions between genotype and daylength on both sleep onset and chronotype, this effect was parsed into specific genotype contrasts (e.g., TT vs. CT and TT vs. CC for P10L). This involved testing for significant difference between slopes describing the relationship between daylength and sleep onset, for example, within a specific genotype, and such specific genotype contrasts are reported above under the interaction effects.

In the additive model, all three genotype groups were compared with one another. In the recessive model, the TT genotype was compared with a group including both CC and CT genotypes together. In the final column, Levene’s test of equality of error variances tested the null hypothesis the error variance of dependent variables is equal across groups, and proved to be not statistically significant in any case, indicating that the variance was not significantly different between genotype groups in any analyses, despite the small number of TT genotypes. Resulting p value of Levene’s test is not less than .05, so the null hypothesis of equal variances is retained, and there is no evidence that there is difference between the variances obtained on the dependent variables when groups are compared by genotype.

p < .05.