JariJ kirjoitti:
Annika Dahlqvist kirjoitti:
Jag fick nu telefon från en person som läst studien. Han berättar att av de 592 kvinnor som dog under studien var 412 rökare. Sådant kallas för confounding factor, förvirrande faktor.
Aika jännä, kommentoi noin kuulopuheen perusteella...
Piti oikein katsoa mitä tästä tupakka-asiasta sanottiin - ja olihan se tietenkin otettu huomioon jo tutkimusasetelmassa:
The participating women and the deaths that occurred amongst them were distributed by non-nutritional covariates, and age- and multivariate- adjusted mortality ratios were calculated. Hazard ratios for overall mortality and mortality from cancer, as well as cardiovascular diseases, were estimated through Cox proportional hazards regression using, alternatively, the high protein score, the low carbohydrate score and the composite additive score as the principal exposure variables. To accommodate secular trends the models were stratified by 1-year birth cohorts with attained age as time scale. In a stratified Cox model the baseline hazard is allowed to vary across strata. The models were adjusted for the following variables as reported at enrolment: height (cm, continuously), body mass index (BMI; <25, 25–29.99 and ≥30 kg m2, categorically),
smoking status (never smokers, former smokers of <10 cigarettes, former smokers of 10–14 cigarettes, former smokers of 15–19 cigarettes, former smokers of 20 or more cigarettes, current smokers of <10 cigarettes, current smokers of 10–14 cigarettes, current smokers of 15–19 cigarettes, current smokers of 20 or more cigarettes, categorically), physical activity [from 1 (low) to 5 (high), categorically], education (0–10, 11–13 and 14 or more years in school, categorically), energy intake (per 1000 kJ day1, continuously), saturated lipid intake (per 10 g, continuously) and alcohol intake (<5, 5–25 or >25 g day1, categorically). Unsaturated lipids should not be and were not controlled for in these models to avoid overdetermination generated by inclusion of all energy-generating nutrients as well as total energy intake in the same models.
Fine control for tobacco smoking was necessary because of the powerful influence of smoking on mortality and the possibility that smoking may be associated with some dietary intakes. All analyses were conducted for all women, as well as separately for women <40 years old at enrolment and for women 40 years or older at enrolment, the rationale being that genetic and early life factors are likely to have a stronger influence amongst younger than amongst older adults.