However, the retrospective nature of this study makes confounding by indication difficult to control.
The presence of a strong association makes confounding a less likely explanation for the results.
Because this was a randomized trial, these patients were likely distributed with similar frequency in both study groups, making confounding unlikely.
However, the retrospective nature of this study makes confounding by indication difficult to control and further studies regarding the timing, dosing, and method of administration are required.
Moreover, the majority of the infants in Sweden have mothers'milk as the only source of nutrition during the first 3 months of life, making confounding of results due to differences in sources of nutrition less pronounced.
To bias the results, a variable would need to be associated with daily changes in air pollution and also be a risk factor for neonatal hospitalization for asthma, making confounding unlikely.
Torreón, on the other hand, has a year-round sunny climate with less seasonal variation, making confounding by seasonality less likely, though still possible; for example, the association between U and 25(OH D was no longer significant after adjusting for season.
Many factors are associated with women's BMI and pregnancy weight gain, such as diet, physical activity, and socioeconomic status (11), but few such factors are known to influence their children's risk of developing islet autoimmunity or type 1 diabetes (12), making confounding by such factors less likely.
Some Muslim Americans say they find themselves having to make a confounding choice.
