View source for WBR0741

{{WBRQuestion
|QuestionAuthor={{YD}} (Reviewed by {{YD}})
|ExamType=USMLE Step 1
|MainCategory=Biostatistics/Epidemiology
|SubCategory=Cardiology
|MainCategory=Biostatistics/Epidemiology
|SubCategory=Cardiology
|MainCategory=Biostatistics/Epidemiology
|SubCategory=Cardiology
|MainCategory=Biostatistics/Epidemiology
|MainCategory=Biostatistics/Epidemiology
|MainCategory=Biostatistics/Epidemiology
|SubCategory=Cardiology
|MainCategory=Biostatistics/Epidemiology
|SubCategory=Cardiology
|MainCategory=Biostatistics/Epidemiology
|SubCategory=Cardiology
|MainCategory=Biostatistics/Epidemiology
|SubCategory=Cardiology
|MainCategory=Biostatistics/Epidemiology
|MainCategory=Biostatistics/Epidemiology
|SubCategory=Cardiology
|Prompt=A cardiologist who interprets echocardiograms notes his observations before he reads the relevant clinical history the patient. After documenting his findings, he retrieves the patient's charts and compares his findings to the patient's clinical data. When asked by his student, the cardiologist replies that this technique is designed to prevent bias. Which type of bias is this technique most likely preventing?
|Explanation=Using the blinded technique, the cardiologist is reducing observer bias (also known as experimenter's bias or researcher's bias). Observer bias is defined as a bias due to the presence of a pre-existing knowledge among the physician/researcher that unconsciously alters results to change the study's outcome. Observer bias is also seen in clinical trials when an investigator knows beforehand which group of subjects is receiving a specific medication; this knowledge might unconsciously influence investigator to alter his findings to match the study's expectations. In this vignette, the cardiologist is documenting his findings blindly to reduce the observer-expectancy effect induced by observer bias.
|AnswerA=Procedure bias
|AnswerAExp=An example of procedure bias is when subjects of two arms of a study experience a different course during the study or are treated differently.
|AnswerB=Lead-time bias
|AnswerBExp=An example of lead-time bias is when early detection is misinterpreted as increased survival.
|AnswerC=Recall bias
|AnswerCExp=An example of recall bias is when a person experiencing a disease might know more of the disease than subjects who do not experience the disease.
|AnswerD=Selection bias
|AnswerDExp=An example of selection bias is when subjects are selected in a non-random fashion.
|AnswerE=Observer bias
|AnswerEExp=An example of observer bias is when the researcher is aware beforehand of what to expect and is unconsciously influenced by his knowledge.
|EducationalObjectives=An example of observer bias is when the researcher is aware beforehand of what to expect and is unconsciously influenced by his knowledge. Blind experimentation reduces observer bias.
|References=First Aid 2014 page 55
|RightAnswer=E
|WBRKeyword=Observer, Bias, Blind, Experiment, Technique, Observer-expectancy bias, Observer expectancy bias, Observer bias, Experimenter bias, Experimenter's bias, Researcher bias, Researcher's bias, Influence
|Approved=Yes
}}