Table 2 Sources of bias
Source of bias | Description |
|---|---|
A | Vaccination affects the probability of NFARI, i.e. ρ β ≠1. This may result from virus interference [6]. |
B1 | Health status affects the probability of NFARI, i.e. η β ≠1. |
B2 | Health status affects the probability of FARI, i.e. η γ ≠1. |
BS | Health status affects the probability of FARI and NFARI, and the risk ratios comparing a healthy and a frail person are the same for both types of ARI, i.e. η β =η γ ≠1. This is a special case of \(B1 \bigcap B2\). |
C | Vaccination affects the probability of seeking medical care for FARI, while it does not affect the probability of seeking medical care for NFARI, i.e. Ψ F ≠1. This may result from reduced severity of symptoms in vaccinated influenza patients. |
D | Health status affects the probabilities of seeking medical care against FARI and NFARI, i.e. λ≠1. |