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Occupational Therapy: An Evidence-Based Approach




Categories of Clinical Questions

Different types of clinical questions have certain kinds of studies that best answer them. The chart below lists the categories of clinical questions and the studies you should look for to answer them.




Types of studies we are going to cover all fall under one of two categories - primary sources or secondary sources. Primary sources are those that report original research and secondary sources are those that compile and evaluate original studies.

Primary Sources

Randomized Controlled Trials are studies in which subjects are randomly assigned to two or more groups; one group receives a particular treatment while the other receives an alternative treatment (or placebo). Patients and investigators are "blinded", that is, they do not know which patient has received which treatment. This is done in order to reduce bias.

Cohort Studies are cause-and-effect observational studies in which two or more populations are compared, often over time. These studies are not randomized.  

Case Control Studies study a population of patients with a particular condition and compare it with a population that does not have the condition. It looks the exposures that those with the condition might have had that those in the other group did not.

Cross-Sectional Studies look at diseases and other factors at a particular point in time, instead of longitudinally. These are studies are descriptive only, not relational or causal. A particular type of cross-sectional study, called a Prospective, Blind Comparison to a Gold Standard, is a controlled trial that allows a research to compare a new test to the "gold standard" test to determine whether or not the new test will be useful.

Case Studies are usually single patient cases.  

Secondary Sources

Systematic Reviews are studies in which the authors ask a specific clinical question, perform a comprehensive literature search, eliminate poorly done studies, and attempt to make practice recommendations based on the well-done studies.

Meta-Analyses are systematic reviews that combine the results of select studies into a single statistical analysis of the results.

Practice Guidelines are systematically developed statements used to assist practitioners and patients in making healthcare decisions.  

The PICO Model

PICO is a useful way of formulating clinical research questions and a well-build question or problem should include the four components of the model: Patient/Problem, Intervention, Comparison and Outcome

PICO Linguist is a tool from the NLM that lets you search for research with terms that incorporate the PICO model. Using it, you can limit your search results to certain types of studies (clinical trials, randomized controlled trials, etc.) or to practice guidelines. 

Patient/Problem   Describe the patient.  Important descriptors might include: age and gender.  Then describe the problem the patient is experiencing.  For example, you might say, "A four-year-old boy with asthma"
Intervention Describe the treatment you are considering for the patient.  This may be a drug, such as "theophylline" for the child with asthma
Comparison Ask yourself what main alternative therapy exists for the problem.  Example: "inhaled glucocorticosteroids"
Outcome Ask yourself what result you want to see because of the therapy.  Example: "decreased hospitalizations and school abscences"


Who cares about your topic?

Who cares about your will help you figure out what type of research they do. (scientists will perform experiments, doctors may run a randomized controlled trial, a professor might write a literature review, etc)

Once you figure the type of resources someone who cares about your topic would create, you can then determine where you will find these resources. (scholarly articles can be found in databases, news articles can be found online, etc)

Brainstorming Keywords

Start by by thinking about the main ideas that are related to your topic.  The PICO format (Population, Intervention, Comparison, Outcome) can help you think about these concepts.

Consider using synonyms of your keywords to help find even more information. For example, if you are looking for articles about the benefits of exercise for patients with heart disease, you might start with the keywords and synonyms below:

Keyword Synonym 1 Synonym 2
heart disease cardiovascular disease
exercise fitness physical activity

Searching for Keywords

Creating a grid like the one above can also help you enter your keywords when you're searching in the databases.  

Try Boolean Operators...

  • "Or" broadens your search results.  (Citrus OR Oranges OR Lemons OR Tangerines OR Grapefruit)
  • "And" narrows your search results. (Rainfall AND Deforestation AND Brazil)
  • "Not" narrows your search results. (Wound healing NOT Plants) (Social media NOT Facebook)
  • "Not" can be used to weed out biased words or phrases associated with your topic. (immigrants NOT illegal aliens)
  • Combine operators for more complex searching. (Coastal sage scrub AND fire OR Postfire OR Postburn)


  • Broadens your search
  • Enter the root of a word and put the truncation symbol at the end.
  • The database will return results that include any ending of that root word. (teen* = teens, teenager, teenagers, teenaged.  environment* = environments, environmental, environmentalist)


  • Broadens your search.
  • Use if a word can be spelled several different ways but has the same meaning.
  • Wom*n = women, woman,  col*r = color, colour

One way to keep track of your research results is to use a research log. This way you will remember where you searched, the keywords you used, and how many results you got.