Have students think about subtle sources of selection


Have students think about subtle sources of selection. For example, have them generate reasons for not dividing people into treatment and no-treatment group based on whether:

(a) their first name ends in a vowel or consonant (more women´s names end in vowels);
(b) their last name begins with A-M or N-Z (some ethnic groups have more last names beginning with letters in the first part of the alphabet, others have more last names beginning with letters in the latter part of the alphabet);
(c) they smoke or not (in addition to other differences, smokers eat more white bread, sugar, whole milk, and fewer fruits and vegetables than nonsmokers); or
(d) they sit in the front or back of the classroom.


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