An insurance company is reviewing its current policy rates. When originally setting the rates they
believed that the average claim amount was $1,800. They are concerned that the true mean is actually
higher than this, because they could potentially lose a lot of money. They randomly select 40 claims, and
calculate a sample mean of $1,950. Assuming that the standard deviation of claims is $500, and set ® = :05,
test to see if the insurance company should be concerned.
Solution
² Step 1: Set the null and alternative hypotheses
H0 : ¹ · 1800
H1 : ¹ > 1800
² Step 2: Calculate the test statistic
Z = x ¡ ¹0
¾=
p
n
=
1950 ¡ 1800
500=
p
40
= 1:897
² Step 3: Set Rejection Region
Looking at the the picture below, we need to put all of ® in the right tail. Thus,
R : Z > 1:96
² Step 4: Conclude
We can see that 1:897 < 1:96, thus our test statistic is not in the rejection region. Therefore we
fail to reject the null hypothesis. We cannot conclude anything statistically significant from this test,
and cannot tell the insurance company whether or not they should be concerned about their current
policies.