Difference in admission rates may be due to other factors

EDITOR—Strachan et al found an interesting difference between admissions to hospital for childhood asthma between twins and singletons.1 They conclude that there is reduced risk of asthma among twins. We found no significant difference in questionnaire based asthma diagnoses between singletons and twins aged 30–59 years among the Finnish twin cohort, but we did not give figures.2 The Finnish twin cohort is a population based sample of adult twin pairs of the same sex selected from the central population registry of Finland as pairs of individuals with the same birth date and sex, as well as the same surname and local community …