Table 1.

Strengths, limitations and assumptions of each study design in estimating heritability (h²) of psychiatric disorders

Study design	Strengths	Limitations	Assumptions
National sibling design (h2–national)	Implicitly includes effects of common and rare genetic effects	No info on actual causal genetic variants	Equal shared sibling environment, also for half siblings
	Psychiatric status based on clinical diagnosis	Needs large samples sizes (tens of thousands of cases) to be able to estimate heritability	Random mating
			Reflection of general population
			No gene × environment interaction
			No gene × environment correlation
SNP-based design (h2-SNP)	Based on measured genetic variants	Includes (a priori) tagged common genetic effects only	Random mating
	No confounding with shared environmental factors	Needs large samples sizes (hundreds of thousands of cases and controls) to be able to extract small genetic effects	Reflection of general population
	Psychiatric status based on clinical diagnosis		No gene × environment interaction
			No gene × environment correlation