This preview shows page 1. Sign up to view the full content.
Unformatted text preview: about the Population Mean: σ known Decision rule will evaluate how likely it is to get a sample with x = 2.5 if you
¯
population mean of 3 years.
.5 2
¯
We know X ∼ N (3, (125) ) if µ = 3 were true.
¯
Then the question is: If so what is the probability of getting an X ≤ 2.5? Well we
can calculate that!
¯
P ( X < 2 .5 ) = P ( Z < 2.5 − 3
) = P (Z < z ) = P (Z < −1.66)
0 .3
z test statistic We can calculate this probability using the ztable. It is 0.0485: the probability that
you get a sample that produces an x which is equal to or lower than than our
¯
current estimate x = 2.5 if the null hypothesis were true.
¯
This is a small probability, so we should probably think that H0 is false. But what is
a small probability?
We need a criteria for small probability. We will call this criteria signiﬁcance level
and denote it with α.
α is in researcher’s control and usually set it to be 0.1, 0.01 or 0.05.
If you calculate a probability for your sample which is less than α, you reject the null
hypotesis.
This is the essence of pvalue approach
Utku Suleymanoglu (UMich) Hypothesis Testing 12 / 37 Testing Hypothesis about the Population Mean: σ known Graphical recap: 0 Utku Suleymanoglu (UMich) Hypothesis Testing z 13 / 37 Testing Hypothesis about the Population Mean: σ known pvalue Approach for OneTailed Tests We are working on the case: tests for µ where σ is known, but this logic generalizes to
many cases.
1. After hypotheses statement and the calculation of test statistic (z for this case) :
2. Calculate
Lefttailed tests: Calculate (lefttail) probability that the sample mean is less than x
¯
at hand if the null is true via: P (Z ≤ z ).
Righttailed tests: Calculate (righttail) probability that the sample mean is more than
x at hand if the null is true via: P (Z ≥ z ).
¯ 3. The probability you calculate is called the pvalue.
4. Compare the pvalue with α.
If pvalue < α : Reject the H0 . You have enough evidence that H0 is false.
If pvalue > α : Fail to reject H0 . There is not enough evidence to reject the null
hypothesis. 5. In our example, we reject the null if α is set to be 0.05 or 0.1 but not if 0.01.
pvalue approach allows easy comparison of decision with diﬀerent α’s.
6. Notice: pvalue is the smallest α choice where H0 is rejected. Utku Suleymanoglu (UMich) Hypothesis Testing 14 / 37 Testing Hypothesis about the Population Mean: σ known Critical Value Approach for OneTailed Tests Another equivalently valid approach to create to criteria for testing would be this:
1. After hypotheses statement and the c...
View
Full
Document
This note was uploaded on 03/17/2014 for the course ECON 404 taught by Professor Staff during the Spring '08 term at University of Michigan.
 Spring '08
 STAFF

Click to edit the document details