Table 2 The advantages and disadvantages of different cohort study types
Study type | Data source(s) | Advantages | Disadvantages |
|---|---|---|---|
Retrospective | Pre-existing insurance databases | - Relatively cheap | - Non-standardised diagnostic criteria |
- Relatively quick | - Poor generalisability in countries with high uninsured population | ||
- May assess multiple clinical exposures and outcomes | - No requirement for insurance data to be made available | ||
- May assess long latent periods | |||
- Recruitment and retention simple | |||
| Â | Pre-existing databases from secondary veterinary hospitals | - Relatively cheap | - Non-standardised diagnostic criteria |
- Relatively quick | - Non-standardised recording systems | ||
- May assess multiple clinical exposures and outcomes | - No knowledge of wider environmental exposures | ||
- Potential to use ancillary resources | - Potential for referral and geographical bias | ||
- May assess long latent periods | |||
- Good for examining serious illnesses | |||
- Recruitment and retention simple | |||
| Â | Pre-existing databases from primary veterinary clinics | - Relatively cheap | - Non-standardised diagnostic criteria |
- Relatively quick | - Non-standardised recording systems | ||
- May assess multiple clinical exposures and outcomes | - No knowledge of wider environmental exposures | ||
- Recruitment simple | - Potential for retention bias as owners move practices | ||
Prospective: Time Limited | According to study protocol: May include investigators, veterinarians, breeders and owners | - Costs and time limited according to length of the study | - Necessarily time limited so unable to assess long-term exposures and long latent periods |
- May assess multiple exposures and outcomes including wider environmental exposures | - Recruitment not simple | ||
- Good for the study of infectious diseases | |||
- Diagnostic criteria set according to study protocol | |||
- Retention bias is minimised | |||
Prospective: Single issue | According to study protocol: May include investigators, veterinarians, breeders and owners | - Potential to examine a single issue in great detail | - Not quick |
- Diagnostic criteria set according to study protocol | - Potentially very expensive | ||
- May assess wider environmental exposures | - Recruitment not simple | ||
- Potential for retention bias in uncontrolled conditions | |||
- May only examine multiple exposures OR multiple outcomes | |||
Prospective: Hypothesis generation | According to study protocol: Animals typically population-based but data maybe generated by investigators, veterinarians, breeders and owners | - May assess multiple exposures and outcomes including wider environmental exposures | - Not quick |
- Diagnostic criteria set according to study protocol | - Not cheap | ||
- Potential to describe health and lifestyle of current population | - Delay to results and lack of specific focus make funding difficult | ||
- Potential to assess the broad impact of lifestyle on disease | - Recruitment not simple | ||
- Potential to generate new hypotheses | - High susceptibility to retention bias | ||
- Potential for poor diagnostic accuracy if reliant on owner-reporting |