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QUESTION 7 When subjects and investigators are both blinded it is known as: a. Explanatory blinding b. Double blinding c. Differential blinding d. Single blinding QUESTION 8 Non-response bias , a. occurs when groups in the source population are left out or underrepresented on the population list used to select the sample O b. occurs when self-selected participants are atypical of the population c. Occurs when a large percentage of selected individuals refuse to participate or cannot be contacted Od. never occurs