It is important to be purposeful about creating a well-built clinical question so that you will be able to find the most relevant results possible. A well-built question will address four important items: Patient or Problem, Intervention, Comparison, and Outcome. To help you remember this, you can use the mnemonic PICO. When you are designing your clinical question, here are some topics to take into consideration.

P= Patient or Problem:

How would you describe a group of patients similar to yours? What are the most important characteristics of the patient? This may include the primary problem, disease, or co-existing conditions. Sometimes the gender, age or race of a patient might be relevant to the diagnosis or treatment of a disease.

I= Intervention: 

Which main intervention, prognostic factor, or exposure are you considering? What do you want to do for the patient? Prescribe a drug? Order a test? Order surgery? Or what factor may influence the prognosis of the patient - age, co-existing problems, or previous exposure? 

C= Comparison: 

What is the main alternative to compare with the intervention? Are you trying to decide between two drugs, a drug and no medication or placebo, or two diagnostic tests? Your clinical question may not always have a specific comparison.

O= Outcome: 

What can you hope to accomplish, measure, improve or affect? What are you trying to do for the patient? Relieve or eliminate the symptoms? Reduce the number of adverse events? Improve function or test scores?

Using our clinical scenario, we will use PICO to develop a clinical question.

Question: In patients with type 2 diabetes and obesity, does bariatric surgery promote the management of diabetes and weight loss as compared to standard medical care?

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.

In our clinical scenario, we are want to determine whether or not bariatric surgery will benefit the patient, so this is a therapy question. As such, we will want to find randomized control trials to answer our question. If we found numerous RCTs on this topic, we might want to consider searching for a systematic review that synthesizes the results of these trials.

The strength of the evidence produced varies among the different types of studies. Filtered sources like systematic reviews and meta-analyses provide stronger evidence because they evaluate and compare a number of original studies. The image below demonstrates the relative strengths of the study types - generally, the higher up on the pyramid you go, the more rigorous the study design and the lesser likelihood of bias or systematic error.

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.