Help with null hypothesis and T-Statistics

#1
Hi:) ,

I'm having problems understanding null hypothesis and t-statistics. Especially this question(below):

12. You will have complete sales information for last month in a week, but right now you have data from a random sample of 40 stores. The mean change in sales in the sample is +3.8% and the standard deviation of the changes is 12%. Are average sales for all stores different from last month?

a. State appropriate null and alternative hypotheses. Explain how you decide between the one-and two-sided alternatives.
H0: µ = .038
Ha: µ ≠ .038

I used the two-sided alternative because it wants to know if the average sales for all stores are different from last month.

b. Find the t statistics and its P-value. State your conclusion.
t = X¯ - .038/(.12/√40 )= 2.00




P-value = .052

Answer: t=2 and p=.052

Are these answers right?

Please help and Thank You
 
Last edited:
#2
Hi,

I also have one more question:

If the test gives strong evidence against the null hypothesis, would you conclude that sales are up in every one of your stores? Explain your answer.

Is dependant on whether the p-value < or > α.

Thank You:)
 
#3
i think you want Ho = 0 in other words the null hypothesis is that no change has occurred.

the answer to your second post is found by considering the standard deviation of your sample.

cheers
jerry
 

JohnM

TS Contributor
#4
jena2007 said:
If the test gives strong evidence against the null hypothesis, would you conclude that sales are up in every one of your stores? Explain your answer.
No - the inference helps you make statements regarding the average sales increase, but tells you nothing about individual stores.
 
E

elnaz

Guest
#5
Hello
yes, your first answers are true ,but about second question if i have understood true , no .