Is the study design appropriate to answer your question?

When considering whether a paper answers your question, you should try to establish whether the methods used in the paper are appropriate. More information is given below, or you can go back to ASK
Type of question Example question Study type that will best answer the question*
Treatment In [dogs with osteoarthritis], does [supplementation with glucosamine and chondroitin] compared to [no supplementation] [reduce lameness]? Randomised controlled trial
Prognosis and Incidence In [flat-coated retrievers with cutaneous lymphoma], does [being a male] compared with [being a female] affect [average life expectancy]? Cohort study
Aetiology and Risk In [ferrets], is [general anaesthesia by triple injectable agent] compared with [general anaesthesia by induction and inhalational agent] associated with [an increased risk of death]? Cohort study, Case-control study, Cross- sectional study
Diagnosis In [lactating dairy cattle] does [milk ELISA] compared with [serum ELISA] have [a better sensitivity and specificity for diagnosing fascioliasis]? Diagnostic test validation study
Prevalence In [adult racehorses] what is the [prevalence of laryngeal neuropathy] in winter? Cross-sectional study

* For all question types, meta-analysis and systematic reviews are more robust than individual studies.

A brief description of the common study types are outlined below in the table (adapted from Dean 2013). When reading a paper, it is important to read the methods section to determine what type of study was conducted; this may sometimes differ from the description in the title or abstract! It is important to understand what was done so that you can determine whether the method was appropriate to answer your question. Be aware that if you read around the subject of study design, you may find different descriptions; epidemiologists are still arguing about what constitutes what study type. This basic description is provided to help you interpret papers you find, and explain the meaning of the terms as used in this tutorial.

Study type Description (adapted from Dean 2013)
Meta-analysis A meta-analysis is a quantitative statistical analysis (generally) conducted as part of a systematic review. By combining the data, a meta-analysis provides more evidence than each individual study is able to on its own.
Systematic review

 

A systematic review is a defined and rigorous method of collating and summarising the information from all published papers addressing a particular question. The methods used to search the literature, assess the quality, and make conclusions are explicitly stated in the methods section.
Randomised controlled trial A randomised controlled trial is an intervention study used to assess a treatment or other intervention. Study subjects are randomly allocated to either the intervention group or a control group (which receives either no treatment, a placebo, the current best treatment or a comparator). Ideally, the study should be ‘blinded’ so that anyone involved with the animals does not know which treatment each animal received.
Cohort study A cohort study is an observational study where exposed and unexposed groups (cohorts) are followed over a period of time. At the end of the study period, the outcome (e.g. disease) is measured. Cohort studies can identify risk factors associated with disease and estimate incidence.
Case-control study A case-control study is a retrospective study comparing animals with the disease (cases) and without the disease (controls) of interest. The animals’ histories are examined to identify risk factors for the disease.
Cross-sectional study A cross-sectional study looks at a sample of the population at a single point in time, most commonly to determine the prevalence of a certain disease.
Diagnostic test validation study A diagnostic test validation study is used to establish the usefulness of new diagnostic tests. Animals are tested using the new diagnostic test and the current gold standard to establish the sensitivity, specificity and likelihood ratios for the new diagnostic test.
Case series A case series is a description of the presentation, diagnosis, treatment and outcome of a group of animals with the same disease. There are no disease-free animals for comparison, and any differences in management are not randomly allocated (for example, they may be due to the owners’ preferences or different protocols between centres).
Case report A case report is a description of a single case (or small number of cases).
Expert opinion Expert opinion can be one individual’s opinion or part of an elicitation process based on a panel of experts used to answer a question of interest. Expert opinion may provide some evidence where no information is available (e.g. new treatment efficacy or application to a new population).