Blinding

• Blinding:

  • controls for biases that may occur after randomisation due to people know what the study is about
• Blinding:

  • concealing the identity of the experimental condition
  • single blind helps minimise the chances of any placebo effects (psychological effects)
  • double blind consists of also blinding the researcher, so they dont know which patient gets the experimental or control group, minimising Rosenthal effects
  • triple blind consists of also blinding the assessors, so they dont bias the outcome towards their views, minimising Rosenthal effects
• Drop Out and Protocol Violation:

  • another type of bias that can occur after randomisation
  • Participants often do not complete the treatment or withdraw from trials
  • Often this is not at random, so the benefits of randomisation are lost
  • Clear reporting and appropriate management of violation and dropout is vital
  • For example, in a trial of Constraint induced therapy versus usual rehab the CIT group experience high drop-out because
  • Unable to tolerate constraint
  • Don’t feel they are making progress
  • this can cause the outcome to look as if CIT is not as effective as it actually can be
• Drop Out and Protocol Violation:

  • questions to ask:
  • How many people dropped out and when?
  • Why did they drop out?
  • Was there a big difference in drop-out between groups?
  • How were any missing data managed?
• Intention to treat versus per protocol:

  • Per protocol: only participants who complete the trial/ treatment to which they were randomised are analysed
  • Intent to treat: (ITT) All participants who were randomised are entered into the analysis regardless of violation or withdrawal