Question

Researchers collected a simple random sample of the times that 81 college students required to earn their bachelor's degrees. This sample has a mean of 4.8 years and a standard deviation of 2.2 years. Use a 0.05 significance level to test the claim that the mean time for all college students is greater than 4.5 years.

Answer 1

Answer:

$t=\frac{4.8-4.5}{\frac{2.2}{\sqrt{81}}}=1.227$    

$p_v =P(t_{(80)}>1.227)=0.1117$  

If we compare the p value and the significance level given $\alpha=0.05$ we see that $p_v>\alpha$ so we can conclude that we have enough evidence to fail reject the null hypothesis, so we can't conclude that the true mean is higher than 4,5 years at 1% of signficance.  

Step-by-step explanation:

Data given and notation  

$\bar X=4.8$ represent the sample mean

$s=2.2$ represent the sample standard deviation

$n=81$ sample size  

$\mu_o =4.5$ represent the value that we want to test

$\alpha=0.05$ represent the significance level for the hypothesis test.  

t would represent the statistic (variable of interest)  

$p_v$ represent the p value for the test (variable of interest)  

State the null and alternative hypotheses.  

We need to conduct a hypothesis in order to check if the mean is higher than 4.5, the system of hypothesis would be:  

Null hypothesis:$\mu \leq 4.5$  

Alternative hypothesis:$\mu > 4.5$  

If we analyze the size for the sample is > 30 but we don't know the population deviation so is better apply a t test to compare the actual mean to the reference value, and the statistic is given by:  

$t=\frac{\bar X-\mu_o}{\frac{s}{\sqrt{n}}}$  (1)  

t-test: "Is used to compare group means. Is one of the most common tests and is used to determine if the mean is (higher, less or not equal) to an specified value".  

Calculate the statistic

We can replace in formula (1) the info given like this:  

$t=\frac{4.8-4.5}{\frac{2.2}{\sqrt{81}}}=1.227$    

P-value

The first step is calculate the degrees of freedom, on this case:  

$df=n-1=81-1=80$  

Since is a one side test the p value would be:  

$p_v =P(t_{(80)}>1.227)=0.1117$  

Conclusion  

If we compare the p value and the significance level given $\alpha=0.05$ we see that $p_v>\alpha$ so we can conclude that we have enough evidence to fail reject the null hypothesis, so we can't conclude that the true mean is higher than 4,5 years at 5% of signficance.