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Lecture 9

HLTC15 Lecture 9 & 10

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Health Studies
Suzanne Sicchia

HLTC15 –Introduction to Quantitative and Qualitative Health Research Methodologies Lecture 9/10: Quantitative Methods III: RCTs and Experimental Methods (Chapter 12 & 13) Tuesday, November 6, 2012 & Tuesday, November 13, 2012 Experimental Designs  “In an experiment, [the researcher] investigates the relationship between two or more [variables] by deliberately producing a change in one of them and ... observing, the change in the other” (Definition adapted from Robson, 1973)  Attempt to test causation rather than association Types of Research Designs Classifying Experimental Designs Randomized Controlled Trials  Prospective, Experimental Design: o Commonly used in Clinical (laboratory) Research o Scientifically Rigorous o Provides the best Source of Evidence for Therapeutic Benefit RCTs and the Hierarchy of Evidence Key Characteristics  Scientific method of hypothesis testing  Sample of a population of interest is randomly assigned to one or more clinical interventions (“arms”) o E.g., control/placebo and intervention/treatment  Preferably (double) blind  Samples are followed up for a specified period of time – observed in an identical manner  Ideally, only difference between groups is the intervention  Groups then analyzed in terms of pre-defined outcomes Basic Structures of Randomized Controlled Trials Implicit Assumptions  Knowledge evolves and develops – contingent, never definitive  Research methods evolve and change – knowledge gained is incremental and likely modest  Cause precedes effect (A leads to B)  Beliefs cannot influence random events  Researcher’s beliefs cannot influence the outcome in well-designed studies  Good research aims to minimize the effects of bias, chance variation, and confounding Refining the Research Question  Quality and precision of the question is central to RCTs  Good questions are explicit, focused, and feasible  A single, well-defined primary question and a few secondary questions (not too many, should also be well-defined)  Good questions are derived from extensive knowledge of the literature (past research – findings, strengths, weaknesses, gaps)  Arriving at a good question is an iterative process  Flushed out and articulated in the research protocol  Clinical knowledge evolves slowly; cannot be rushed for many reasons Developing Viable RCTs  Structure, rationale and design largely formulated on existing evidence – as outlined in the research protocol  Investigation is carried out by research teams (regular consultation)  Literature review is continuous – does not end with protocol  Pilot or feasibility study can refine research question, sampling and recruitment strategy, test appropriateness of measurements, etc.  Statistical determination of required sample size (for statistical power, impacts generalizability)  Ensure randomization and blinding are possible Methodological Challenges  Feasibility: Time, Money, Instruments, Measurements, etc.  Ethical Considerations: Informed Consent, Denial of Treatment, Risk of Harm  Avoiding Bias at all Stages of the Trial  Randomization and the Control of Confounding Methodological Challenges: Bias Bias Description Counter-Measures 1. Recruitment Bias Non-representative population used for Sampling recruitment 2. Selection Bias Intervention and control groups are not Sample comparable 3. Performance Bias Groups within the intervention arm receive Standardization; High degree of different kinds of treatment Coordination across sites 4. Detection Systematic differences in the outcome Standardization of Outcome, assessment between groups Measurements, Instruments 5. Attribution Bias Withdrawals distort symmetry of the initial Transparency and Record Keeping: selection process and this skew results full reporting of withdrawals to avoid distortion 6. Researcher/Participant Bias Influence of knowing which arm of a study Binding (Hawthorne Effect) participants are in Methodological Challenges: Confounding  Occurs when there is an association between an exposure to an intervention and the outcome as a consequence of an intervening variable  Counter Measure: randomization  Neutralizes effects of confounding by equally distributing potential confounders between groups  Other counter measures: sample size and make-up, procedures (proper vetting, thorough data collection, )  Example: mortality attributed to lung cancer, age, smoking history RCT Phases (Progressive steps in RCTs)  In Vivo and In Vitro Research  Pre-Clinical Trials  Phase I - RCT  Phase II - RCT  Phase III – RCT Pre-Clinical Trials (in vivo and in vitro)  In vivo = research in a non-human living organism  In vitro = in a petri dish (cells, etc.)  Used to identify and minimize risk to humans and maximize therapeutic value of a given treatment  Many such experiments before clinical trials in humans  Useful for ADME of a drug: o Assessing absorption of a drug o Metabolic effects of a drug o Distribution of a drug through the body o Extent of Excretion Phase I RCTs  Population is not randomized  Carried out in individuals with pre-existing pathology  Used to establish the maximum tolerated dose by increasing dose of medication in patients with real pathology and to look for side effects  To assess the safety and efficacy of the treatment  Criteria used to define ‘max. tolerated dose’ and ‘tx efficacy’ varies greatly (e.g., cancer patients versus migraine sufferers) Phase II RCTs  Extends the work of Phase I  Looks at different doses to find the dose that provides the best clinical effect with the lowest level of adverse reaction  Also car
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