Randomised Controlled Trials
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This document discusses randomised controlled trials (RCTs) and their use in evaluating health care interventions. It provides background on James Lind, who in 1747 conducted one of the earliest known clinical trials to test treatments for scurvy. The document outlines key aspects of RCTs such as defining the research question, population, interventions, and outcomes, as well as the importance of randomization and blinding to reduce bias. It distinguishes between explanatory and pragmatic trials and notes RCTs are generally considered the gold standard for evaluating health care technologies.
Randomised Controlled Trials
- 1. Randomised Controlled Trials (RCTs) Graeme MacLennan
- 2. James Lind Born Edinburgh 1716 On HMS Salisbury in 1747 he allocated 12 men with scurvy Cider Seawater Horseradish, mustard, garlic Nutmeg Elixir Vitriol Oranges and Limes
- 3. Think about… Consider how you would go about evaluating the following interventions Surgical versus medical termination of pregnancy Referral guidelines for radiographic examination Paracetamol and/or ibuprofen for treating children with fever Nurse counsellors as an alternative to clinical geneticists for genetic counselling Single dose of chemotherapy versus radiotherapy treating testicular cancer http://news.bbc.co.uk/1/hi/health/7647007.stm Cervical cancer vaccine http://news.bbc.co.uk/1/hi/health/6223000.stm
- 4. The need to evaluate health care Variations in health care Unproven treatments Inadequacies in care Inaccurate medical models Limitation of resources New innovations … Crombie (1996)
- 5. Evaluation process Define research question What is already known? Identify appropriate study design Define population, intervention and criteria for evaluation How large a study? Consider measurement of evaluation criteria (“outcomes”) How often? Timing? Length of follow up? To whom? Who collects the data? What format? Analysis of data Dissemination and implementation
- 6. Define research question and what is already known Research question (PICOT) Population Intervention Control/comparator Outcome Target Has the question already been answered? Conduct review to assess what is know about intervention
- 7. Definition of population, intervention and “outcomes” Population Strict definition (explanatory) or flexible (pragmatic) Intervention Dose of drug, timing etc “ Outcomes” Health related Quality of Life Biochemical outcomes Symptoms Physical assessment Patient satisfaction Acceptability Cost-effectiveness
- 8. Measuring “outcome” Questionnaires, interview, medical notes etc Timing of questionnaires? Baseline (prior to treatment) Short term outcomes Long term outcomes Who collects the data?
- 9. Sources of systematic errors Selection bias can be introduced by the way in which comparison groups are assembled Attrition bias systematic differences in withdrawal/follow up Performance bias Systematic differences in care provided Observation/detection bias systematic differences in observation, measurement, assessment
- 10. What is a randomised controlled trial? Simple Definition A study in which people are allocated at random to receive one of several interventions (simple but powerful research tool)
- 11. Simple RCT model RANDOMLY allocated to experimental or CONTROL group CONTROL EXPERIMENT Trial participants
- 12. What is a randomised controlled trial? Random allocation to intervention groups all participants have equal chance of being allocated to each intervention group why RCTs are referred to as randomised controlled trials
- 13. Terminology Interventions are comparative regimes within a trial Prophylactic, diagnostic, therapeutic e.g. preventative strategies screening programmes diagnostic tests drugs surgical techniques
- 14. What is a randomised controlled trial? One intervention is regarded as control treatment (the group of participants who receive this are the control group) NOTE: Contemporaneous (not historical controls) why RCTs are referred to as randomised controlled trials
- 15. Terminology Control Group can be conventional practice no intervention (this may be conventional practice) placebo Experimental Group receive new intervention (also called treatment group or intervention group interchangeably)
- 16. What is a randomised controlled trial ? RCTs are Experiments: investigators can influence number, type, regime of interventions Quantitative: measure events rather than try to interpret them in their natural settings Comparative: compare two or more interventions
- 17. What is a randomised controlled trial? More Complex Definition Quantitative, comparative, controlled experiments in which a group of investigators study two or more interventions in a series of participants who are allocated randomly to each intervention group
- 18. Inclusion/exclusion criteria Decision rules applied to potential trial participants to judge eligibility for inclusion in trial See CONSORT statement www.consort-statement.org Important that they are applied identically to all groups in a trial!
- 19. What is randomisation? Randomisation is the process of random allocation Allocation is not determined by investigators, clinicians or participants Equal chance of being assigned to each intervention group Individual people patients caregivers (physicians, nurses etc) Groups of people, ‘cluster randomisation’ (Covered in more depth in later lecture)
- 20. Pseudo-randomisation Other allocation methods include according to date of birth the number on hospital records date of invitation etc. These are NOT regarded as random These are called pseudo- or quasi-random
- 21. Terminology Controlled clinical trials (CCTs) are not the same as randomised controlled trials Controlled clinical trials include non-randomised controlled trials and randomised controlled trials
- 22. Why use randomisation? Characteristics similar across groups at baseline can isolate and quantify impact of interventions with effects from other factors minimised Risk of imbalance not abolished completely even if perfect randomisation To combat selection bias Unpredictability paradox: review of empirical comparisons of randomised and non-randomised clinical trials, Kunz and Oxman 1998 BMJ http://www.bmj.com/cgi/content/abstract/317/7167/1185
- 23. Why do we need a control group? Don’t need a control group if completely predictable results Parachutes when jumping from plane New drug cures a few rabies cases But No intervention has 100% efficacy Many diseases recover spontaneously
- 24. Regression to the mean Occurs when an intervention aimed at a group or characteristic that is very different from average For example selecting people because they have high blood pressure then measuring them in future will see the blood pressure measurements closer to the mean of the population Morton and Torgerson BMJ 2003 326:1083-4 Bland and Altman BMJ 1994 308:1499 and 309:780
- 25. DISTRIBUTION OF RESULTS threshold measurement 1 measurement 2
- 26. Hawthorne Effect Experimental effect in the direction expected but not for the reason expected Essentially studying/measuring something can change what you studying/measuring
- 27. Placebo Effect Effect (usually, but not always positive) attributed to the expectation that a therapy will have an effect The effect is due to the power of suggestion A placebo is an inert medication or procedure Waber et al 2008 JAMA Commercial Features of Placebo and Therapeutic Efficacy http://jama.ama-assn.org/cgi/content/full/299/9/1016
- 28. EFFECT OF AN INTERVENTION Effect size Experimental group Control group Hawthorne E. R. mean Placebo E. Therapeutic E. Real difference Noise Signal
- 29. Minimising bias in RCTs Blinding Single blind – participants are unaware of treatment allocation Double blind – both participants and investigators are unaware of treatment allocation Requires use of placebos in drug trials Schulz and Grimes (2002)
- 30. Concealment of random allocation list “ Trials with inadequate allocation concealment have been associated with larger treatment effects compared with trials in which authors reported adequate allocation concealment” Schulz KF (1995). Subverting randomisation in controlled trials. JAMA, 274, 1456-8
- 31. Blinding, placebos RCTs should use the maximum degree of blinding that is possible Placebo is a ‘dummy’ treatment given when there is no obvious standard treatment needed as the act of taking a treatment may have some effect -need to attribute double blind treatments must be indistinguishable to those affected
- 32. Empirical evidence of bias
- 33. ‘ Explanatory’ and ‘Pragmatic’ questions Explanatory Can it work in an ideal setting …..? Efficacy Hypothesis testing Placebo controlled Double blind Pragmatic Does it work in the real world …..? Effectiveness Choice between alternative approaches to health care Standard care Open
- 34. Key differences between explanatory and pragmatic trials (1) Explanatory Pragmatic Question efficacy effectiveness Setting ‘laboratory’ normal practice Participants strictly defined broader, clinically indicated (uncertainty) Interventions strictly defined as clinical practice
- 35. Key differences between explanatory and pragmatic trials (2) Explanatory Pragmatic Outcomes short-term long-term, patient- surrogates centered and resource orientated Size small (usually larger single centre) (often multi-centre) Analysis treatment received intention to treat Relevance indirect direct to practice
- 36. Example of selection bias for PP in an open trial Exp Ctrl None None White(2005) E E Worse prognosis
- 37. Terminology: explanatory versus pragmatic Explanatory trials estimates efficacy - that is the benefit the treatment produces under ideal conditions Pragmatic trials estimates effectiveness - that is the benefit the treatment produces under routine clinical practice Roland M, Torgerson D. What are pragmatic trials? BMJ 1998;316:285
- 38. RCT as the Gold Standard The randomised controlled trial is widely regarded as the gold standard for evaluating health care technologies because it allows us to be confident that a difference in outcome can be directly attributed to a difference in the treatments and not due to some other factor
- 39. RCT strengths Confounding variables minimised Only research design which can in principle yield causal relationships can clarify the direction of cause and effect Accepted by EBM school Don’t have to know everything about the participants
- 40. RCT limitations Contamination of intervention groups Comparable controls Problems with blinding What to do about attrition? Are patients/professionals willing to be in trial different from ‘refusers’?- external validity Cost!
- 41. Other issues in RCTs (1) Ethics Management issues Interim analysis and ‘stopping rules’ part of ethical concern mechanisms to avoid patient harm Data Monitoring and Safety Committee required for trials Clemens F et al Data monitoring in randomised controlled trials: surveys of recent practice and policies. Clin Trials 2005;2(1):22-33.
- 42. Other issues in RCTs (2) A power calculation is essential for the validity of a trial and will always be necessary for grant applications and in publications of the trial (later lecture) The methods of randomisation should always be reported. It is not enough to say that the patients were randomly allocated to the treatments. (see CONSORT)
- 43. Parallel group (simple) RCT design in practice Patient eligible for either treatment Patient gives informed consent Yes No Randomise Exclude from trial Experimental treatment Standard treatment Standard treatment
- 44. Summary “ Gold standard” of research designs Individual patients are randomly allocated to receive the experimental treatment (intervention group) or the standard treatment (control group) Maximises the potential for attribution Randomisation guards against selection bias between the two treatment groups Standard statistical analysis Good internal validity May lack generalisability due to highly selected participants Can be costly to set up and conduct, ethical issues
- 45. Good study design General considerations maximise attribution Ensure no factor other than the intervention differs between the intervention and control group Random allocation, if adequately carried out, will in the long run ensure comparable groups with respect to all factors minimise all sources of error systematic error (bias) random error (chance) be practical and ethical
- 46. Minimise sources of error Systematic errors (bias) “ inaccuracy which is different in its size or direction in one of the groups under study than the others ” Minimise bias by ensuring that the methods used are applied in the same manner to all subjects irrespective of which group they belong to. Random errors (chance) “ Inaccuracy which is similar in the different groups of subjects being compared” Adequate sample size, accurate methods of measurement Elwood (1998)
- 47. Study designs Experimental (Randomised controlled trial) A new intervention is deliberately introduced and compared with standard care Quasi-experimental (non-randomised, controlled before and after) Researchers do not have full control over the implementation of the intervention (“opportunistic research”) Observational (Cohort, case-control, cross-sectional) describes current practice observed differences cannot be attributed solely to a “treatment” effect
- 48. Evaluation of health care interventions Randomised controlled trials are considered as the “gold standard” However, some debate over the advantages and disadvantages of different research designs for assessing the effectiveness of healthcare interventions Polarised views “ observational methods provide no useful means of assessing the value of a therapy” (Doll, 1993) RCTs may be unnecessary, inappropriate, impossible or inadequate (Black, 1996) Approaches should be seen as complementary and not as alternatives (Black, 1996) Interpretation of RCTs in terms of generalisability
- 49. Useful/interesting links www.jameslindlibrary.org (History) www.consort-statement.org (CONSORT) www-users.york.ac.uk/~mb55/pubs/pbstnote.htm (All the stats notes from BMJ) www.ctu.mrc.ac.uk (MRC CTU) www.rcrt.ox.ac.uk (under construction) Doll R. Clinical Trials the 1948 watershe BMJ 1998;317:1217-1220 The unpredictability paradox: review of empirical comparisons of randomised and non-randomised clinical trials Regina Kunz and Andrew D Oxman BMJ 1998 317: 1185-1190
- 50. References Black. Why we need observational studies to evaluate the effectiveness of health care. BMJ 1996 : 312;1215-8 Crombie. Research in Health Care. 1996 Doll. Doing more good than harm: the evaluation of health care interventions. Ann NY Acad Sci 1993:703;310-13 Elwood M. Critical appraisal of epidemiological studies and clinical trials. 1998 OUP; Oxford. Greenhalgh T. How to read a paper. 2001 BMJ; London Schulz and Grimes. Lancet Epidemiology series. 2002