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Table 2 The advantages and disadvantages of different cohort study types

From: What can cohort studies in the dog tell us?

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
  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
  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