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6. Randomised controlled trial

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This is the lecture notes for Randomized controlled trial (HFS3063)

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6. Randomised controlled trial

  1. 1. KNOWLEDGE FOR THE BENEFIT OF HUMANITYKNOWLEDGE FOR THE BENEFIT OF HUMANITY PUBLIC HEALTH AND EPIDEMIOLOGY (HFS3063) Epidemiological Study Designs: RANDOMISED CONTROLLED TRIALS Dr.Dr. MohdMohd RazifRazif ShahrilShahril School of Nutrition & DieteticsSchool of Nutrition & Dietetics Faculty of Health SciencesFaculty of Health Sciences UniversitiUniversiti SultanSultan ZainalZainal AbidinAbidin 1
  2. 2. Topic Learning Outcomes By the end of this lecture, students should be able to; • describe randomised controlled trial design. • explain the advantages and disadvantages of randomised controlled trial design. 2
  3. 3. Randomized controlled trials (RCT) • RCT or randomized clinical trials are experimental studies where the effect of an intervention is assessed by collecting data before and after an intervention. • Used to compare an intervention with one or more other intervention or with no intervention. • Intervention are often clinical treatments but may also be educational interventions (e.g. health promotion leaflets). • Two main features of the RCT; a) They are comparative b) They are designed to minimize bias 3
  4. 4. a) Comparative • In RCT, an intervention is investigated by comparing one group of people who receive the intervention with a control group or control arm who do not. • Control group receives usual or no treatment and their outcome measure (or the change in measure from the baseline) is compared with that of the intervention group. 4
  5. 5. 5
  6. 6. b) Minimizing bias in RCT 1) Allocation bias 2) Performance bias 3) Assessment bias 4) Attrition bias 5) Allocation concealment 6
  7. 7. 1) Allocation bias • Occurs when the measured treatment effect differs from the true treatment effect because of how participants were selected into the intervention or control group. • In RCT, participants will be randomized to either an intervention or control group at study entry. • Randomization ensures that characteristics that might affect the relationship between intervention and outcome measures will be roughly equal across all arms of the study – minimizing potential bias 7
  8. 8. 2) Performance bias • Occurs when participants’ response to the treatment is affected by knowledge of the group to which they are assigned. – They know which group they belongs to either intervention or control. • Performance bias might also occur when health professionals administer treatment differently between treatment arms. 8
  9. 9. 3) Assessment bias • Health professionals assessing the outcome of treatment relative to alternative or placebo interventions may record outcome measures biased by the knowledge of the group assignments. • Overestimation or underestimation of the effects on an intervention is known as assessment bias. • There might be a systematic difference in measuring the outcomes between the two groups because of the method of recording used – E.g. control group is assigned to one practitioner and the intervention group to another, or groups are assessed at different times of the day. 9
  10. 10. (cont.) 3) Assessment bias • How to minimize the assessment bias? – Use a standardized method of evaluation across both groups. – Avoid using subjective measures to assess the effectiveness of a treatment which are more prone to bias. 10
  11. 11. 4) Attrition bias • Also called as loss-to-follow-up bias. • Occurs when patients drop out of the study from their respective study group. • If halfway through a study the treatment has been successful, participants may drop out and information about the success of the treatment is then lost. • Participants in the control group might be unhappy with their lack of progress and may drop out of the study in order to seek alternative help. 11
  12. 12. 5) Allocation concealment • Bias will be minimized where the allocation schedule is concealed of whom is assigned to which group. • Blinding (or masking) helps prevent systematic differences between comparison groups in prognosis or responsiveness to treatments (allocation bias). • Blinding of both participants and practitioners prevents performance and assessment bias by ensuring everybody (participants, treatment admin, those measuring outcomes) do not know which treatment was given. • It is recommended RCT participants are blind to the treatment they receive. – Control group receives placebo 12
  13. 13. Why carry out RCT? • RCT are prospective longitudinal studies – Allowing causal association between intervention and outcomes. • The random selection of participants into each arm and the controlled way in which trial is carried out mean that all factors are considered equal. • Other study design cannot infer causality. 13
  14. 14. Important factors in RCT? 1) Sample size 2) Stratification 3) Trial design 4) Between group contamination 5) Ethical issues 14
  15. 15. 1) Sample size • Sample size dependent upon – the power of the test – what size of intervention impact is considered meaningful – type of hypothesis the RCT is testing • The smaller magnitude of difference between groups that is to be detected and the greater the variability in outcomes, the larger the sample size that will be required. 15
  16. 16. 2) Stratification • Very large trials are likely to have a good balance of patients within each arm. • When samples are small, however, treatment groups may be chance end up with different characteristics – May affect the outcome trial • Stratification is a way of ensuring the treatment groups are balanced on characteristics that are likely to alter the relationship between treatment and outcome. 16
  17. 17. 3) Trial design • There are two commonly used trial design to allocate treatment and control regimens in RCT; – Parallel design – Crossover design • In parallel design, different patients will be randomized in each treatment group. – There will be differences in characteristics of participants 17
  18. 18. (cont.) 3) Trial design • Crossover trials are another way of overcoming differences in groups by keeping the patients as matched as possible. • Instead of having different patients in each treatment group, patients receive first one treatment and then the other, in random order, with a wash out period in between. 18
  19. 19. (cont.) 3) Trial design • Within-patient differences are then compared in crossover design. • Each patient effectively becomes their own ‘test’ and ‘control’. 19
  20. 20. 4) Between group contamination • Educational interventions are prone to contamination e.g. a member of the control arm is a friend of a patient receiving the low fat diet advice intervention. – Information will be passed between the two arms of trial and thus alter results. • Use cluster sampling so natural cluster such as geographic areas are randomized rather than individuals. 20
  21. 21. 5) Ethical issues • RCT is not always possible because of ethical issues when assigning patients to study arms. • If one group of patients receives treatment thought to be effective, while another group does not, the ethics of a trial may be brought into question. • Similarly, there are some trials that cannot be carried out because they may actively encourage unhealthy practices e.g. smoking. – People cannot be randomized into smoking and non-smoking group. 21
  22. 22. Analysis of data • RCT are experiments set up to test hypotheses. • Null hypotheses – the intervention will have no impact on the outcome measure – Outcome will be similar in both the test and control groups • Alternative hypotheses – intervention will have meaningful effect and statistically significant • Statistical method (e.g.); – Pre and post intervention differences = paired t-test – Mean differences pre and post between two group = independent t-test – Mean differences pre and post between more than two groups = ANOVA 22
  23. 23. Advantages of RCT • Ability to make causal inferences mean that RCT provide the strongest empirical evidence of a treatment’s efficacy. • Randomization of participants to the test and control arms and concealment of their allocation ensures that allocation bias and confounding or unknown variables are minimized. • The study can be tailored to answer a specific question. 23
  24. 24. Disadvantages of RCT • High dropout when the intervention has undesirable side-effects or there is little incentive to stay in the control arm. • Ethical consideration may mean that a research question cannot be investigated using RCT design • For a descriptive overview it may be cheaper and easier to use an observational design. • Prior knowledge is required for sample size calculation; – the level of improvement that is clinically meaningful – expected variation of improvement in the sample 24
  25. 25. Recapitulate In this lecture, you have been exposed to; • definition of RCT • how biases is minimized in RCT • factors to be considered when carrying out RCT • analysis of data for RCT • advantages and disadvantages of RCT 25
  26. 26. Thank YouThank You 26
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This is the lecture notes for Randomized controlled trial (HFS3063)


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