MA 213
Fall 2007
Professor: Michael J. Pencina
Practice midterm 2  Solutions
1.
Double Multiple Choice:
in the following questions exactly
two answers are correct.
If you give two correct answers you get 4 points;
if you give only
one answer and it is correct you get two points;
if you give two answers, one correct and one incorrect, you get only 1 point;
in all other situations you get zero points.
1.1 Which two are true:
A) We are trying to prove, support or detect the null hypothesis;
B) The level of significance is equal to the probability of the margin of error;
C) The level of significance if equal to the probability of type I error;
D) Type I error is committed if we reject the null if it is false;
E)
Type I error is committed if we reject the null if it is true;
1.2 We measured the pulse rate for each individual in a random sample of 23.
Assume we have all the
measurements.
A) The 95% confidence interval (CI) for pulse rate would use a critical value of z=1.96;
B) The 95% confidence interval (CI) for pulse rate would use a critical value of t=2.069;
C) The 95% confidence interval (CI) for pulse rate would use a critical value of t=2.074;
D) Since the population standard deviation is unknown we cannot construct a 95% CI for pulse rate;
E)
To construct the 95% CI we need to assume that pulse rate is approximately normal.
1.3 Let t1 and t2 be such numbers that P(t ≥ t1) = 0.025 and P(t ≤ t2) = 0.05.
A) If degrees of freedom are 10 then t1 = 2.228;
B) If degrees of freedom are 10 then t1 =  2.228;
C) If degrees of freedom are 13 then t2 = 1.771;
D) If degrees of freedom are 13 then t2 = 1.761;
E) t1 > t2 regardless of the degrees of freedom.
1.4 Assuming all other parameters are constant, in order to cut the margin of error in half we need to:
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