Types of research studies 

There are lots of different types of medical research, not all of them involve people. The results of research studies is usually (but not always) published in clinical journals or on special websites.  These are available for doctors and nurses and other health workers to read and learn from.

The main types of research involving people are:

  • Randomised control trials 
  • Prospective cohort studies

Randomised control trials

These are the gold standard in clinical research.  People are randomly assigned to different groups.  Each group receives a different treatment or procedure.  The outcomes from each group are compared over a particular time period.  These trials are designed to test a theory. They do this by changing only one thing but keeping all the groups similar in every other respect.

Crossover randomised controlled trials

In a crossover trial people are swapped from one treatment to the opposite treatment after a period of time.  There is usually a “wash out” period between the two treatments.

Prospective cohort studies

Here there is no intervention.  After recruitment and baseline tests, people are observed over time and further measurements and tests conducted.  These observations may go on for years.  The results from these studies have to be treated with caution as they can be affected by many things including diet and lifestyle.  These studies can only ever suggest a relationship between a particular behaviour and a risk factor, condition or another medical outcome.  

What is a systematic review or meta-analysis?

Sometimes researchers will review all the available literature on a specific subject to see if collectively it answers a particular research question or strengthens the available evidence for or against a treatment.
  
In a systematic review researchers identify specific criteria to describe the type of research they want to review.  They use this to help them search for and identify relevant research.   They usually reject poor quality data, or any studies they find that do not fit their strict criteria.  They then systematically appraise the data.
  
In a meta-analysis similar studies are combined together and a mathematical analysis is made of the results. 

Results from systematic reviews and meta-analysis can often help to identify patterns in the research data and can strengthen our understanding.  But like individual research trials these too can be of variable quality.              

Why conduct clinical research
Who can take part in a clinical trial
Questions to ask before taking part in a clinical trial
How are clinical trials planned and organised
How are clinical trials supervised