22nov2011 - CR Long C502 Biostatistical Thinking 22 Nov...

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CR Long C502: Biostatistical Thinking 22 Nov 2011 Learning Objectives 1. Recognize 2 common methods of minimizing systematic error: randomization and blinding Terminology Selection Bias A systematic error or bias that causes a sample to be unrepresentative of the target population. Randomization Random Sample : a subset of a population where each study unit is independently chosen and has a known non-zero chance of being selected. Purpose: to eliminate systematic differences in the choice of study units to be included in the sample (i.e. selection bias ) Note: a statement not about the sample, but rather the method that produced the sample. Random Allocation to Treatment : each study unit has a known non-zero chance of being assigned to one treatment or another, but the study units do not necessarily make up a random sample (are usually a convenience sample) . Purpose: to eliminate systematic differences in the distribution of important characteristics (e.g. demographics, prognostic factors) between treatment groups
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22nov2011 - CR Long C502 Biostatistical Thinking 22 Nov...

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