A 62-year-old man with a history of dyslipidemia and type 2 diabetes mellitus comes to the emergency department due to severe substernal chest pain and diaphoresis that began 2 hours ago. His ECG shows ST- segment elevation in leads V1 to V4. He is taken to the cardiac catheterization lab and a complete occlusion of the mid-left anterior descending artery (LAD) is diagnosed. A drug-eluting stent is placed in the LAD with complete restoration of flow, and the patient is started on aspirin and clopidogrel. On the third day of hospitalization, the option of adding rivaroxaban is discussed with the patient. He asks about the benefits and risks of the added therapy. Based on the research abstract, The statistical methods section of the full research paper indicates that the analysis was performed using an "intention-to-treat" approach. The primary purpose of such an approach is most likely which of the following?
A)Decrease the placebo effect
B)Eliminate observer bias
C)Enhance external validity
D)Preserve randomization
E)Reduce type II errors

Question

A 62-year-old man with a history of dyslipidemia and type 2 diabetes mellitus comes to the emergency department due to severe substernal chest pain and diaphoresis that began 2 hours ago.  His ECG shows ST- segment elevation in leads V1 to V4.  He is taken to the cardiac catheterization lab and a complete occlusion of the mid-left anterior descending artery (LAD) is diagnosed.  A drug-eluting stent is placed in the LAD with complete restoration of flow, and the patient is started on aspirin and clopidogrel.  On the third day of hospitalization, the option of adding rivaroxaban is discussed with the patient.  He asks about the benefits and risks of the added therapy.  Based on the research abstract, The statistical methods section of the full research paper indicates that the analysis was performed using an "intention-to-treat" approach.  The primary purpose of such an approach is most likely which of the following?
A)Decrease the placebo effect
B)Eliminate observer bias
C)Enhance external validity
D)Preserve randomization
E)Reduce type II errors

Quizplus · Accepted Answer

Explanation: Important features of randomized clinical trials are randomization (eg, to eliminate bias in treatment assignments), blinding, and intention-to-treat (ITT) analysis. The basic premise of ITT analysis is that participants in trials should be analyzed in the groups to which they were randomized, regardless of whether they received or adhered to the allocated intervention and regardless of whether they withdrew from treatment. The ITT principle holds that randomization is of paramount importance and that deviation from the original randomized groups can contaminate the treatment comparison. ITT analyses are performed to avoid the effects of crossover and dropout, which may break randomization and affect the outcome. For example, if the sickest patients drop out at a higher rate, even an ineffective treatment may appear beneficial if analysis is performed on only those who finished the treatment. (Choice A) The placebo effect is the phenomenon whereby a patient's symptoms are alleviated by an otherwise ineffective treatment (placebo), most likely due to the individual expecting the treatment to work. The ITT principle does not affect the placebo effect. (Choice B) Observer bias occurs when the observer may be influenced by prior knowledge or details of the study that can affect the results. Blinded studies, such as this one, usually avoid this bias by preventing the observers from knowing which treatment or intervention the participants are receiving, thereby measuring outcomes more objectively. (Choice C) The generalizability or external validity of a study reflects the applicability of the obtained results beyond the cohort that was studied. External validity is dependent on the adequacy of the sample. If the sample is representative of the desired population, then the results will generalize. Although ITT analysis can improve the external validity by including the entire sample originally selected for the trial (regardless of participation or compliance with the intervention), the primary purpose of ITT is to preserve randomization rather than to enhance external validity. (Choice E) Type II error represents failure to reject a null hypothesis when it is false. Type II errors are dependent on the power of a study, which is in turn dependent on sample size. As the sample size and power increase, the likelihood of a type II error decreases. Educational objective: The basic premise of the intention-to-treat principle is that participants in trials should be analyzed in the groups to which they were randomized, regardless of whether they received or adhered to the allocated intervention and regardless of whether they withdrew from treatment. References: Intention-to-treat analysis in clinical trials: principles and practical importance. (http://www.ncbi.nlm.nih.gov/pubmed/12522981)

A 62-Year-Old Man with a History of Dyslipidemia and Type