Modeling gene-environment interactions in longitudinal family studies: a comparison of methods and their application to the association between the IGF pathway and childhood obesity

Table 2 Characteristics of the analysis sample

	No. of individuals	Proportion or Mean (SD)
Individuals	536
Individual average BMI	536	15.09 (1.59)
Age
At birth	536	0 (0)
Follow-up #1	536	6.28 (0.74)
Follow-up #2	531	19.49 (0.75)
Follow-up #3	497	31.77 (0.96)
Follow-up #4	435	49.85 (1.82)
Follow-up #5	478	62.25 (3.23)
Zygosity^a
DZ twin	149	0.51
MZ twin	143	0.49
Sex^a
Female-female twin	122	0.42
Male-male twin	102	0.35
Female-male twin	68	0.23
Physical Activity
More	156	0.37
Equal	253	0.59
Less	17	0.04
Individual proportion of follow-up attending daycare facility	530	0.42 (0.37)
Individual proportion of follow-up with sufficient sleep	524	0.57 (0.31)
Race
Caucasian	518	1
Other	0	0

^aAnalysis conducted with respect to each twin pairs instead of individuals
No number, SD standard deviation, BMI body mass index, MZ monozygotic, DZ dizygotic

ISSN: 1471-2350