In: Statistics and Probability
A new kind of typhoid shot is being developed by a medical research team. The old typhoid shot was known to protect the population for a mean time of 36 months, with a standard deviation of 3 months. To test the time variability of the new shot, a random sample of 21 people were given the new shot. Regular blood tests showed that the sample standard deviation of protection times was 1.3 months. Using a 0.05 level of significance, test the claim that the new typhoid shot has a smaller variance of protection times.
(a) What is the level of significance?
State the null and alternate hypotheses.
Ho: σ2 = 9; H1: σ2 > 9Ho: σ2 = 9; H1: σ2 < 9 Ho: σ2 < 9; H1: σ2 = 9Ho: σ2 = 9; H1: σ2 ≠ 9
(b) Find the value of the chi-square statistic for the sample.
(Round your answer to two decimal places.)
What are the degrees of freedom?
What assumptions are you making about the original
distribution?
We assume a uniform population distribution.We assume a exponential population distribution. We assume a binomial population distribution.We assume a normal population distribution.
(c) Find or estimate the P-value of the sample test
statistic.
P-value > 0.1000.050 < P-value < 0.100 0.025 < P-value < 0.0500.010 < P-value < 0.0250.005 < P-value < 0.010P-value < 0.005
(d) Based on your answers in parts (a) to (c), will you reject or
fail to reject the null hypothesis?
Since the P-value > α, we fail to reject the null hypothesis.Since the P-value > α, we reject the null hypothesis. Since the P-value ≤ α, we reject the null hypothesis.Since the P-value ≤ α, we fail to reject the null hypothesis.
(e) Interpret your conclusion in the context of the
application.
At the 5% level of significance, there is insufficient evidence to conclude that the new typhoid shot has a smaller variance of protection times.At the 5% level of significance, there is sufficient evidence to conclude that the new typhoid shot has a smaller variance of protection times.
(f) Find a 90% confidence interval for the population standard
deviation. (Round your answers to two decimal places.)
lower limit | |
upper limit |
Interpret the results in the context of the application.
We are 90% confident that σ lies within this interval.We are 90% confident that σ lies below this interval. We are 90% confident that σ lies above this interval.We are 90% confident that σ lies outside this interval.
Answer:
(a) What is the level of significance?
Level of significance = α = 0.05
State the null and alternate hypotheses.
Ho: σ2 = 9; H1: σ2 < 9
We are given σ = 3, so σ2 = 9
(b) Find the value of the chi-square statistic for the sample.
We are given n = 21, S = 1.3
Chi square = (n – 1)*S^2/ σ2= (21 - 1)*1.3^2/9 = 3.7556
Chi square = 3.7556
What are the degrees of freedom?
df = n – 1 = 21 – 1 = 20
What assumptions are you making about the original distribution?
We assume a normal population distribution.
(c) Find or estimate the P-value of the sample test statistic.
P-value = 0.0021
(by using Chi square table)
P-value < 0.005
(d) Based on your answers in parts (a) to (c), will you reject or fail to reject the null hypothesis?
Since the P-value ≤ α, we reject the null hypothesis.
(e) Interpret your conclusion in the context of the application.
At the 5% level of significance, there is sufficient evidence to conclude that the new typhoid shot has a smaller variance of protection times.