In a study by Brown et al in (CMAJ January 31, 2022 194 (4) E112-E121; DOI: https://doi.org/10.1503/cmaj.211277) the authors report on a study "that included adults with COVID-19 who were admitted to hospital and discharged between Jan. 1, 2020, and Nov. 30, 2020, at 7 hospitals in Ontario, Canada". They write "We evaluated clinical outcomes in patients who were admitted to hospital with COVID-19 with a disability compared with patients without a disability".

They found 1279 admissions with COVID of whom 285 or 2.3% "had a recorded disability". For those with a disability 28.1% died in hospital and for those without 17.3% died in hospital.

Question a) Explain why it would be unsafe to conclude that patients with a disability are more likely to die in hospital than are patients without a disability. [2 marks]

Question b) Explain why it would be unsafe to conclude that disabled people are more vulnerable to COVID than are people without a disability. [2 marks]

The authors went on to make the same comparison between patients with a disability and those without a disability separately in two different age groups: those under 65 years of age and those over.

Question c) Explain why they would do this and suggest reasons why the differences in death rates between the two groups would be smaller in each of the age groups than overall.

Can anyone answer these three questions? It is about statistics.