Describe the type of sample selection bias that would result from each of these

Question

Describe the type of sample selection bias that would result from each of these sampling methods.

a) A student wants to determine the average size of farms in a county in Iowa. He drops some rice randomly on a map of the county and uses the farms hit by grains of rice as a sample.

b) In a study about whether valedictorians "succeed in life", a professor "traveled across Illinois, attending high school graduations and selecting 81 students to participate... He picked students from the most diverse communities possible from little rural schools to rich suburban schools near Chicago to city schools".

c) To estimate the percentage of students who passed the first Advanced Placement Statistics exam, a teacher on an Internet discussion list for teachers of AP Statistics asked teachers on the list to report to him how many of their students took the test and how many passed.

d) To find the average length of string in a bag, a student reaches in, mixes up the strings, selects one, mixes them up again, selects another and so on.

e) In 1984, Ann Landers conducted a poll on the marital happiness of women by asking women to write to her.

Explanation / Answer

a. Size bias would result from this sampling method as this would give an higher value for the average size farm.

b. Judgement bias would result as the professor picked students from the most diverse communities possible.

c. Voluntary bias would result as teachers on the list whose students passed are more likely to respond.

d. This would again result in size bias as chances of reaching a longer string is more.

e. Voluntary bias would result as only any women who is happy is more likely to write.

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