Quizes usually have three questions, and each question is worth		
ten points.  They take ten to fifteen minuntes.

Sample Quiz One		

1.  I rolled a six sided cube twice.		

a.  What is the probability that I got two sixes?

b.  What is the probability that the second roll was a 	
six given that the first was a six?


2.  P(E) = .1
    P(D given E) = .4
    P(D given no E) = .05

What is P(D and E)?

3.  There are three children in a family.  The probability that any child
inherited a trait is 1/4.  The events are independent.

a.  What is the probability that no child inherited the trait?

b.  What is the probability that the second child inherited the trait
given that the firstchild inherited the trait?

4.  P(A) = .1
    P(B) = .4
    P(A and B) = .02

What is P(A given B)?

Quiz Two

A random variable has a binomial distribution.  The probability of a
scuccess is .2.  If n = 10, what is the expected number of successes?

2.  Suppose the rate of influenza infections in children is one per year.  

a.  What is the rate for a two year period?

b.  What is the probability that a child will have more than three
episodes in the first two years of life?

Quiz Three

1.  A variable is normally distributed with mean 50 and standard deviation
ten.  Imagine that I draw a very large number of random samples from this
distribution each of size twenty five from this population.

a.  What is the best estimate of the mean of all the sample means
generated by these samples?

b.  What is the best estimate of what the standard deviation of all these
sample means will be?

c.  Suppose I only draw one sample.  The mean is 51.  Put a 95% confidence
bound around it.

2.  Find the t score with ten degrees of freedom that has 90% of the
distribution below it.

3.  A health educator conducted a survey and found that 200 of 500 smokers
want to quit.  

a.  What is the best estimate of the population proportion?

b.  Put a 95% confidence bound around the proportion.

4.  We estimated a mean based on a sample of of 25 people.  We did not
know the population variance so we estimated it from the sample.  What are
the critical values for the following confidence bounds?

a.  90%

b.  95%

c.  99%

Quiz Four

1.  We are testing the hypothesis that a drug elevates serum creatinine.
We will sample 40 people.  We do not know the population standard
deviation.		

a.  What is the critical value if alpha equals .05?  Where is the critical
region:  at the left tail, at the right tail, or at both tails of the
distribution?

b.  Suppose we do not set alpha in advance but try to estimate an exact p
value.  The test statistic equals 2.15.  p < ?

c.  Suppose you used a two sided alternative.  p < ?

2.  We did a one sample t test with 15 degrees of freedom.  The test
statistic equals 1.60.

a.  What is your conclusion if the alternative hypothesis is one sided?

b.  What is your conclusion if the alternative is two sided?

3.  A researcher wanted to test the hypothesis that women with frequent
urinary tract infections had sexual intercourse more often than women
without the infections.  He sampled twenty with infection and asked them
to keep logs for six weeks.  The mean frequency is 2.5 per week and its
standard deviation is 1.5.  Kinsey reported that the national average is
2.3 per week in his famous report.

a.  State the null and the alternative hypotheses.

b.  Compute the test statistic.

c.  State your conclusions.

4.  I want to estimate the power of a test.  The standard error equals 5.
the null hypothesis is that the mean equals 20.  The one sided alternative
is that it equals 30.  the critical value converted to the scale of the
null hypothesis is 28.5.  What is the power of the test?	

Quiz Five

1.  Another researcher explored the relationship between sexual activity
and frequency of urinary tract infection.  She selected twenty patients
with frequent infection and twenty controls.  She asked them to keep logs
for six weeks.  She obtained the following results.

         Infection      No infection
 Mean       2.5            1.9
 s.d.       1.5            1.3

a.  State the null and alternative hypotheses.  Find the critical value
for a .05 level test.

b.  Compute the test statistic and state your conclusion.


2.  A researcher wants to test the hypothesis that students who are
anxious about taking tests will have more variable scores that those who
are not anxious.  He sampled two students whose average socres were the
same.  The anxious student had a variance of 20, and the non-anxious
student had a variance of twelve.  Each variance was based on ten scores.
  
a. State the null and alternative hypotheses.  Find the critical value for
a .05 level test.

b.  Compute the test statistic, and state your conclusion.


3.  We want to test the hypothesis that clinic patients blood pressure
will be higher if it is taken with their legs crossed than it will be if
their legs are not crossed.  We collect data under both conditions for six
patients.

                 Crossed     Uncrossed
                   110         102
                   140         135
                   130         121
                   125         118
                   115         110
                   130         122

a.  Is a paired to test appropriate for this data?

b.  Do a paired t test, and state your conclusion.

c.  Do a two sample t test, and state your conclusion.

Practice for Quiz Six

1.  In a case control study we obtained twice as many controls as cases.
Data was not individually matched.

                   Case   Control
           Exp      40      50
           Not exp  60     150

a.  Find the expected values for the chi square test of independence.

b.  Compute the test statistic, and state your conclusion.

c.  Compute an odds ratio for exposure.

d.  Conduct a two sample test of proportions.