From The Guardian
Researchers compared the medical records of 24,624 people in the US with Parkinson’s, 19,046 people with Alzheimer’s and 23,942 people with cerebrovascular disease.
Those with Parkinson’s were matched with patients in the other groups for age, sex, race and ethnicity, and length of diagnosis to compare the frequency of gastrointestinal conditions in the six years before diagnosis.
1. What is the study design?
2. What is the rationale for selecting people with Alzheimer's?
[Kim Barrett, vice-dean for research at the University of California, Davis] said: “The findings are purely correlative, and it remains possible
that both gastrointestinal conditions and Parkinson’s disease are
independently linked to an as yet unknown third risk factor.”
2. What is the epidemiologic concept she refering to? Explain why this matters.
3. Could you design an RCT to investigate this research question?