Note: The risk of bias by domain corresponds to the highest risk of bias among outcomes by domain.
The overall risk of bias corresponds to the overall highest risk of bias assessed among outcomes.
| Bias | Author's judgement | Support for judgement |
| Confounding |
Serious |
The study matched on age, sex, GP practice and time. The analysis adjusted for care home residence, risk category, number of non-cardiovascular drug classes in past 240 days, recent hospitalisation. Ethnicity, socio-economic status and health-seeking behaviour were not measured and uncontrolled confounding is likely. |
| Selection of participants into the study |
Low |
No particular concerns in this domain. |
| Clasification of interventions |
Low |
No particular concerns in this domain - vaccination status is likely to be adequately measured (obtained from electronic health records). |
| Deviations from intervention |
Low |
No concerns in this domain - the study was observational. |
| Missing outcome data |
Low |
No concerns in this domain - data appear reasonably complete. |
| Measurement of the outcome |
Low |
No particular concerns in this domain - outcome assessment is likely to be adequate. |
| Selection of the reported results |
Moderate |
There is no evidence of a protocol/analysis plan, and we have concerns that results could have been selected for reporting because of the findings. |
| Overall risk of bias |
Serious |
|
| Overall comment | Concerns is over uncontrolled confounding: the estimates were not adjusted for socio-economic status, ethnicity or health-seeking behaviour. |