The following
are examples of errors in the analysis of the sample problem. In each case,
explain what is wrong.
A student is
given the following problem: In the past, about 10% of people were left-handed.
You suspect the percentage is increasing because people are less likely to
dissuade a child from being left-handed these days. You observe a random sample
of 100 first-graders at recess to see whether they throw with their left or
right hand, and you find that 15 use their left hand. What is the probability
that you would observe 15 or more first-graders using their left hand if the
population proportion was still 10%?
She presents
the following calculations. What has the student done wrong in each case?
a. 
= 497
probability
above ≈ 0
b. SD = 
=.03
probability above ≈ 0
c. 
probability above: z = -1.67 is 1 - .0475 = .9525