Iwona Stelmach
['Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data.', 'Is a subgroup effect believable? Updating criteria to evaluate the credibility of subgroup analyses.', 'Iwona Stelmach', 'The BMJ', 'Creative Commons Attribution', 'Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data.']