Veterinary Epidemiology and Zoonosis

RANDOMIZED CONTROLLED TRIALS AND NON RANDOMIZED TRIALS

Randomized controlled trials

• It involves a process of random allocation.
• The basic steps in conducting a randomized controlled trials include the following,
  • Drawing up a protocol
  • Selecting reference and experimental populations
  • Randomization
  • Manipulation or intervention
  • Follow up
  • Assessment of outcome  
• The protocol
  • One of the essential features of a randomized controlled trial is that the study is conducted under a strict protocol.
  • The protocol specifies the aims and objectives of the study, questions to be answered, criteria for the selection of study and control groups, size of the sample, etc.
• Selecting reference and experimental populations
  • Reference or target population: It is the population to which the findings of the trial, if found successful, are expected to be applicable.
  • Experimental or study population: The study population is derived from the reference population.
  • It is the actual population that participates in the experimental study.
• Randomization
  • Randomization is a statistical procedure by which the participants are allocated into groups usually called 'study and control groups', to receive or not to receive an experimental preventive or therapeutic procedure, or intervention.
• Manipulation
  • Having formed the study and control groups, the next step is to intervene or manipulate the study and group by the deliberate application or withdrawal or reduction of the suspected causal factor.
• Follow up
  • This implies examination of the experimental and control group subjects at defined intervals of time, in a standard manner, with equal intensity, under the same given circumstances , in the same time frame till final assessment of outcome.
• Assessment
  • The final step is assessment of the outcome of the trial in terms of positive results and negative results.
  • Randomized controlled trials require follow up of thousands of cases for a decade or more.
  • The cost and logistics are often prohibitive.
  • These trials are rare.

Non-randomized trials

• The approach is sophisticated in randomized controlled trials, it is rather crude in non-randomized trails.
• As there is no randomization in non-experimental trials, the degree of comparability will be low and the chances of a spurious result higher than where randomization had taken place.