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Table 3 Risk of bias in time-trend analyses

From: The quadrivalent HPV vaccine is protective against genital warts: a meta-analysis

First author (year)Risk of selection bias: changes in the study population characteristics between the pre- and post-vaccination periodsRisk of information bias: errors in the identification of HPV+ during the pre- and post-vaccination period (data source, genital wart case definition, outcome used)Risk of confounding:
changes in HPV infection between the pre- and post-vaccination periods could be diluted/exacerbated by other variables
Dominiak-Felden (2015) [17]High
Some people possibly may have been vaccinated without reimbursement (risk of misclassification), imiquimod agreement was used as the date of vaccination.
High
A surrogate marker (imiquimod agreement) was used as definition of genital wart cases (risk of underestimation).
High
Different sexual behaviours between vaccinated and unvaccinated women.
Chow (2015) [28]High
Possible changes in the clientele of the sexual health services between the periods.
Self-reported vaccination status and the number of doses of HPV vaccine.
Low
Clinical diagnosis by clinicians.
High
Clients at sexual health service have higher risk of sexually transmissible infections.
Ali (2013) [27]High
Possible changes in the clientele of the sexual health services between the periods.
Self-reported vaccination status and the number of doses of HPV vaccine.
Low
Genital warts are directly diagnosed by physicians.
High
Changes in sexual activity, health seeking behaviour could potentially cause changes in genital wart frequency over time.
Harrison (2014) [29]Unclear
Some women from the vaccination eligible group may be included with non-vaccine eligible women due to the change in patient age.
Low
Genital wart diagnosis by physicians.
High
Change in sexual risk behaviour.
Read (2011) [31]Unclear
Possible changes in the clientele of the Melbourne Sexual Health Centre.
Low
Genital wart diagnosis by physicians.
Unclear
Possible HPV infection of 21–29 years women before the vaccination.
Fairley (2009) [30]Unclear
Possible changes in the clientele of the Melbourne Sexual Health Centre.
Low
Genital wart diagnosis by physicians.
Unclear
Boys aged 9–15 years could be prescribed the vaccine privately.
Checchi (2019) [32]Unclear
Inability to link anogenital wart diagnoses to individual vaccination status.
Low
Genital wart diagnosis by physicians.
Unclear
Patients could attend elsewhere for treatment of anogenital wart.
Mann (2019) [33]Unclear
Patients’ vaccination status is unknown.
Low
Genital wart diagnosis by physicians.
Unclear
Patients with anogenital wart could choose to seek care elsewhere.