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Randomisation techniques

Different techniques of clinical trial randomization.

Randomisation techniques

  2. 2. Randomization Randomization is the process of assigning clinical trial participants to treatment groups. Randomization gives each participant a known (equal) chance of being assigned to any of the groups. Successful randomization requires that group assignment cannot be predicted in advance.
  3. 3. Need of Randomization • If, at the end of a clinical trial, a difference in outcomes occurs between two treatment groups (say, intervention and control) possible explanations for this difference would include: • the intervention exhibits a real effect; • the outcome difference is solely due to chance • there is a systematic difference (or bias) between the groups due to factors other than the intervention. Randomization aims to obviate the third possibility.
  4. 4. Criteria for randomization 1. Unpredictability • Each participant has the same chance of receiving any of the interventions. • Allocation is carried out using a chance mechanism so that neither the participant nor the investigator will know in advance which will be assigned. 2. Balance • Treatment groups are of a similar size & constitution, groups are alike in all important aspects and only differ in the intervention each group receives 3. Simplicity • Easy for investigator/staff to implement
  5. 5. Simple Randomization 1. Coin Tossing for each trial participant 2. Sequence of Random Numbers from statistical textbooks 3. Computer generated sequence
  6. 6. Egs  The most common and basic method of simple randomization is flipping a coin. For example, with two treatment groups (control versus treatment), the side of the coin (i.e., heads - control, tails - treatment) determines the assignment of each subject.  Shuffled deck of cards (e.g., even - control, odd - treatment)  Throwing a dice (e.g., below and equal to 3 - control, over 3 - treatment).  The computer generated sequence: 4,8,3,2,7,2,6,6,3,4,2,1,6,2,0,……. Two Groups (criterion:even-odd): AABABAAABAABAAA…… Disadvantages: …. Advantages of unequal randomization include the opportunity to place more patients in a less expensive arm, or to place more patients in an arm where there is concern about effects and side effects, i.e. an arm in which more data are needed.
  7. 7. Block randomization • The block randomization method is designed to randomize subjects into groups that result in equal sample sizes. • The block size is determined by the researcher and should be a multiple of the number of groups (i.e., with two treatment groups, block size of either 4, 6). • Example: Two treatments of A, B and Block size of 2 x 2= 4 • Possible treatment allocations within each block are • (1) AABB, (2) BBAA, (3) ABAB, (4) BABA, (5) ABBA, (6) BAAB
  8. 8. Block Randomization Design With 3 Blocks of Size 4, Treatments of A & B • Obs Block Size • 1 1 B • 2 1 A • 3 1 B • 4 1 A • 5 2 A • 6 2 B • 7 2 B • 8 2 A • 9 3 B • 10 3 B • 11 3 A • 12 3 A
  9. 9. • Block size depends on the number of treatments. • The block size is not stated in the protocol so the clinical and investigators are blind to the block size.
  10. 10. DISADV • If blocking is not masked in open-label trials, the sequence becomes somewhat predictable (e.g. 2n= 4): • B A B ? Must be A. • A A ? ? Must be B B
  11. 11. Stratified Randomization • Trial may not be valid if it is not well balanced across prognostic factors. • SR means block within block For example, Age Group: < 40, 41-60, >60; Sex: M, F • For 6 patients in a block, Total number of strata = 3x2=6. • It produce comparable groups with regard to certain characteristics (e.g., gender, age, race, disease severity), thus produces valid statistical tests
  12. 12. • The block size should be relative small to maintain balance in small strata. • Increased number of stratification variables or increased number of levels within strata leads to fewer patients per stratum. • Subjects should have baseline measurements taken before randomization. • Large clinical trials don’t use stratification
  13. 13. Unequal Randomization • Most randomized trials allocate equal numbers of patients to experimental and control groups. • This is the most statistically efficient randomization ratio as it maximizes statistical power for a given total sample size. • However, this may not be the most economically efficient or ethically/practically feasible. When two or more treatments under evaluation have a cost difference it may be more economically efficient to randomize fewer patients to the expensive treatment and more to the cheaper one. • The substantial cost savings can be achieved by adopting a smaller randomization ratio such as a ratio of 2:1, with only a modest loss in statistical power.
  14. 14. Ratio to be used • When one arm of the treatment saves lives and the other such as placebo/medical care only does not much to save them in the oncology trials. The subject survival time depends on which treatment they receive. More extreme allocation may be used in these trials to allocate fewer patients into the placebo group. • Generally, randomization ratio of 3:1 will lose considerable statistical power, more extreme than 3:1 is not very useful, which leads to much larger sample size.
  15. 15. Inappropriate randomization methods • Assigning patients alternately to treatment group is not random assignment • Assigning the first half of the population to one group is not random assignment • Assignments by methods based on patient characteristics such as date of birth, order of entry into the clinic or day of clinic attendance, are not reliably random
  16. 16. Issues leading to Blinding • Most investigators know about treatments effectiveness and select it for particular groups of patients. As a result, Investigators channel particular groups of patients to particular treatments (channeling effect ) • There is a risk of the investigators subconsciously losing their objectivity in their assessments of treatment effects simply because of their knowledge about treatment. • There is a risk of having other forms of BIAS, which can be satisfactorily controlled by proper blinding .
  17. 17. Bias Bias is said to have occurred if the results observed reflect other factors in addition to the effect of the treatment. Conscious and subconscious factors. Occur at conduct of trail, data analysis and interpretation of data. Some potential sources of bias: • • • • • Patient bias Care Provider bias Assessor bias Laboratory bias Analysis and Interpretation bias
  18. 18. 1. Patient Bias • The patient's knowledge that he is receiving a "new" treatment may substantially affect the patient's subjective assessment • There is a subject and disease interaction
  19. 19. 2. Care Provider Bias • The care provider's knowledge of which treatment a patient is receiving may affect the way the provider – deals with the patient – treats the patient • These differences may give the patient, information (even if incorrect) about the treatment the patient is receiving, affect the outcome of the study
  20. 20. 3. Assessor Bias • The assessor's knowledge of which treatment the patient is receiving may affect the way the assessor assesses outcome • such a bias would directly affect the validity of the conclusions of the study • if the assessment is done while the patient is still receiving treatment, this may provide the patient with information about the treatment being received
  21. 21. 4. Laboratory Bias • The knowledge of which treatment the patient received may affect the way in which the test is run or interpreted, or be retested. • Subjectively graded results (pathology slides, photographs, ECG, etc.).
  22. 22. Analysis and Interpretation bias • Knowledge of the treatment group may affect the results of the analysis of the data by – seeking an explanation of an "anomalous” finding when one is found contrary to the study hypothesis – accepting a "positive" finding without fully exploring the data • Knowledge of the treatment group may affect the decisions made by external monitors of a study by – Terminating a study for adverse events because they were expecting it. – Terminating a study for superiority of treatment because they were expecting it.
  23. 23. Blinding All of these potential problems can be avoided if everyone involved in the study is blinded to the actual treatment the patient is receiving. Blinding (also called masking or concealment of treatment) is intended to avoid bias caused by subjective judgment in reporting, evaluation, data processing, and analysis due to knowledge of treatment.
  24. 24. Hierarchy of Blinding • Open label: no blinding • Single blind: patient blinded to treatment • Double blind: Patient and Physician (and data collectors) blinded to treatment • Complete blind: Everyone involved in the study blinded to treatment
  25. 25. Open Label Studies • • • • • • • These may be useful for • Pilot studies • dose ranging studies Open label studies are not recommended for comparative trials, under certain circumstances, OLS are conducted. e.g. in order to provide some potentially promising medications to the patients with severely debilitating or life-threatening disease. Safety and effectiveness of a new surgical procedure, comparision of devices, changes in life style trials conducted in an open-label fashion. Eg Multiple Risk Factor Intervention Trial for CAD. Adv: Disadv: Eg CA bypass VS medical treatment study
  26. 26. Single Blind Studies • Single blind studies are usually done to blind the patient to the treatment given. Health care providers and assessors usually know the actual treatment given • Justification is usually that double-blind is "impractical" because of need to adjust medication, medication affecting laboratory values, potential side effects, critical condition of the patient etc. Eg Zn therapy to relieve taste disorder • A single blind (Physician) study can also be used when it is unacceptable ethically to give a placebo treatment to a patient, and in such a case, the assessor (not the patient) should be the one blinded to the treatment
  27. 27. Double Blind Studies • When both the subjects and the investigators are kept from knowing who is assigned to which treatment, the experiment is called double blind. • Serve as a standard by which all studies are judged, since it minimizes both potential patient biases and potential assessor biases • Should be used whenever possible.
  28. 28. Double Blinding:Techniques • • • • Coded treatment groups Placebo for each possible treatment. Tablets identical in physical appearance. Tablets with similar taste and smell : use of Quassin for taste masking. • IV infusions would normally be the same carrier as used for active medications. • Other treatments "shammed" as far as possible: eg. Minimal power ultrasound therapy when testing effect of physical therapy in back pain. Eg Vit C trial : double blind trial was broken
  29. 29. Disadvantages: Double Blinding is not always feasible?? When intervention is surgery- It is unlikely that sham surgery would be considered ethical in a study. • It would be hard to blind a patient to the therapy given in an exercise study. • it might not be possible to blind a patient while comparing utility of different invasive procedures
  30. 30. Double Blind Studies: Difficulties Side effects: • Side effects (observable by patient) are much harder to blind • in general, there are significant ethical problems using placebos to induce side effects in patients. • a way to avoid it is that the side effects of all the potential therapies be combined into a single list, so that knowledge of side effects would not indicate therapy (at least to patient). Efficacy: • A truly effective treatment can be recognized by its efficacy in patients. • Some new treatments ARE VERY EFFECTIVE and when this happens, it is becomes clear which treatment a patient is receiving, at least for the health care providers involved in the trial.
  31. 31. Complete Blinding • Patient and the investigator, all members of the clinical project team of the sponsor including CRA, statistician, programmer, and data coordinator are blinded. • May require two groups for data processing, one group to encode the data/analysis and one group to perform the analysis • Normally only available in major drug company studies, and not routinely used.
  32. 32. Complete Blinding:Techniques • Analysis uses coded treatment groups • Analysis uses coded side effects (e.g., side effects coded using non-standard scheme, with only numeric codes available at time of analysis) • Analysis uses coded laboratory tests (e.g., name of test coded numerically at time of analysis, using non-standard code)
  33. 33. Coding of drugs • • • • Assigning a random number. As many as different code. Participants: unique code. If only one code is used: disclose for 1 will disclose for all. • Many side effect in many people: decode • Efficient coding: sd not confuse the prescriber and stocking of drugs.
  34. 34. Unblinding of study • The carton must contain slip of drug inside it. • Should not be disclosed to patients while storage. • Official unblinding may be necessary during emergency.
  35. 35. Assessment of blindness • Ask the participant and cross asking the clinical staff. • 50% of answers exceed.
  36. 36. Recruitment of Study Participants
  37. 37. • Diffficult task: sufficient number of patients in reasonable amount of time. • Eg 39 ONCOLOGY TRIAL: Only 2 trial recruited successfully. • Factors: depends on type and size of trial, length of time available, the setting, single centric/ multicentric trial etc.
  38. 38. • National Institute of Neurological Disorders and Stroke’s (n.d.) notice recruiting participants for a clinical trial titled Study of • Brain Activity During Speech Production and Speech Perception. • The inclusion criteria specified for the experimental group were (a) right-handed children and adolescents, (b) native speakers of American English, and (c) stuttering or phonological processing disorders. The comparison (control) group consisted of normally developing right-handed children and adolescents who were native speakers of American English. Exclusion criteria were (a) language use in the home other than American English, (b) speech reception thresholds greater than 25 dB, and (c) contraindications to magnetic resonance scanning. In a similar fashion, systematic reviewers specify inclusion and exclusion criteria for synthesizing studies, but the criteria are usually much broader.
  39. 39. Inclusion and exclusion criteria • Inclusion and exclusion criteria are the conditions that must be met in order to participate in a clinical trial, or the standards used to determine whether a person may be allowed to participate in a clinical trial. The most important criteria used to determine appropriateness for clinical trial participation include age, sex, the type and stage of a disease, treatment history, and other medical conditions.

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Different techniques of clinical trial randomization.


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