Randomised controlled trial
This is a study in which a group of individuals with the condition of interest are randomly assigned at entry to the trial into one of two (or more) groups. Usually in clinical practice such groups will then receive different treatment regimes. Such trials may be single blind, in which the patient does not know which treatment he is getting, but are preferably double blind in which case the investigator/researcher too does not know what treatment the patient is receiving. This is because of the potential for both a powerful placebo effect and subjective bias in people. You could randomise institutions rather than people, and the principles involved are also used in animal and plant studies.
In medicine the successful delivery of the RCT was the 1948 British Medical Research Council (MRC) trial of streptomycin for the treatment of tuberculosis. The gestation certainly included Scottish surgeon James Lind 1753 publication of a controlled trial that demonstrated that a diet including citrus fruit was effective against scurvy. By the late 19th century, researchers were conducting alternate-allocation trials, with the classic such trial being Johannes Fibiger’s 1898 study of diphtheria antitoxin in 484 patients in Copenhagen. In 1931, James Burns Amberson and colleagues published a trial in which a coin flip randomly determined which of two seemingly equally divided groups of patients would receive sanocrysin for the treatment of tuberculosis. Selection bias stemming from the ease of cheating the process of strict allocation remained the Achilles’ heel of alternate allocation. Austin Bradford Hill, replaced alternate allocation with strict concealed randomization of patients to treatment or control groups due to problematical data from alternate-allocation trials of tuberculosis therapies in the 1930's. The increasing regulation of the medicines industry in the 1970s made the RCT an essential step in new medicine development and contributed to marked improvements in medicines safety.
- Cohort study
- Case control study
- Randomised controlled trial
- PHRU on appraisal of a cohort study
- Social Research Methods website tutorial on cohort studies
- Wikipedia page on cohort studies
- Disease and exposure - includes sections on Odds ratio and Relative risk.