Question

what is the differnce between a one tail z test and a two tail z test? When should we use one over the other?

Answer #1

If the alternative hypothesis in a z-test consists of ‘less than’ or ‘greater than’ type of inequality, then this z-test is said to be a one tailed z test.

If the alternative hypothesis in a z-test consists of ‘not equal to’ type of inequality, then this z-test is said to be a two tailed z-test.

For example:

One tail z test:

H_{0}: µ = 5 vs. H_{a}: µ > 5

Or

H_{0}: µ = 5 vs. H_{a}: µ < 5

Two tail z test:

H_{0}: µ = 5 vs. H_{a}: µ ≠ 5

We should use one tail z-test when alternative hypothesis or research hypothesis wants to show sample mean is less than or greater than that of population mean.

We should use two tail z-test when alternative hypothesis or research hypothesis wants to show sample mean is not equal to that of population mean.

For a two-tail hypothesis test, the test statistic is z = 2.08.
What is the p-value?
For a one-tail hypothesis test, the test statistic is z = -2.18.
What is the p-value?

What is the relationship between the confidence level and the
level of significance of a 2-tail test?
Which Hypothesis Tests use Z distributions?
Which Hypothesis Tests use a Student’s t distribution?

In a one-tail hypothesis test where you reject Upper H 0 only
in the lower tail, what is the p dash value if upper Z subscript
STAT baseline equals negative 1.05?

In
a one tail hypothesis test where you tehect Ho only in the lower
tail what us the critical value of the Tstat test statistic w/ 26
degrees of freedom at the .01 level if significance? (Round to 4
decimal places)

If you use a 0.05 level of significance in a two-tail
hypothesis test, what decision will you make if ZSTAT=+2.09?

For a one-tail (lower) test for a single population, we do not
reject the null if the test statistic is greater than or equal to
the negative of the critical value.
True or false

4. What is the difference between “z” and “t” statistics? When
do we use z-table, and when do we use t-table?

Imagine a utility company shared population variance for all
LEED and non-LEED certified buildings in their database. If we want
to compare water usage between two samples of LEED-certified and
non-LEED certified buildings for which we have data, what type of
test should we use and why? What is the main benefit of using this
type of test? Interpret the findings.
Gallons of Water Used per Hour LEED-Certified
Buildings
(in thousands of gallons)
Gallons of Water Used per Hour non...

What is the F-critical value for a one-tail F-test if the
numerator sample size is 21 (n1) and the denominator
sample size is 16 (n2); use level of significance (α)
0.05.
Select one:
a. 3.37
b. -3.99
c. 2.33
d. 3
To test the effectiveness of a business school preparation
course, 8 students took a general business test before and after
the course. The results are given below.
Exam
Score
Exam Score
Student Before Course
(1) After Course (2)...

1. Consider a two tail
test at the α =0.01 significance level with a test statistic ztest=
-1.98.
a) use the critical
value approach to decide weather to reject ho
b) use the p value
approach to decide weather to reject ho

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