Table 1.

Possible outcomes of a dual analysis process

Row	A1	A2: + weight	Conclusion	Insight
1	+	-	Absolute phenotype ∆	No longer significant–confounded by BW
2	-	-	No abnormality
3	-	+	Relative phenotype ∆	Adding weight increases sensitivity to detect ∆
4	+	+	Absolute phenotype ∆ and relative phenotype ∆	Two scenarios
				1. BW difference: still there is a significant ∆ as ∆ larger/smaller than expect for BW difference
				2. BW same: a significant ∆. Weight explains variation but does not lead to phenotype difference.

Possible outcomes when assessing for a genotype effect for a variable of interest when the analysis excludes (A1) or includes body weight as a covariate (A2). In this table, + indicates a statistically significant genotype effect;−indicates a non-significant genotype effect; ∆ indicates change; BW indicates body weight