Question

You collect data on two independent simple random samples from approximately normal populations. The summary statistics are: n1 = 7, = 7, s1 = 2, n2 = 9, = 4, and s = 1.9. You think the population standard deviations are equal, so you decide to pool the estimates of the population standard deviation of the difference between the means. Which of the following gives the correct t statistic for a pooled test of the hypothesis H0 : µ1 − µ2 = 0, and the number of degrees of freedom upon which this is based?

Answer 1

T-statistic = 3.068

Degree of Freedom = 14

Explanation:

We are given the following in the question:

Group 1:

`\mu_1 = 7\\\sigma_1 = 2\\n_1 = 7`

Group 2:

`\mu_2 = 4\\\sigma_2 = 1.9\\n_2 = 9`

First, we design the null and the alternate hypothesis

`H_(0): \mu_1 - \mu_2 = 0\\H_A: \mu_1 - \mu_2\\eq 0`

Since, the population variances are equal and that the two populations are normally distributed, we use t-test(pooled test) for difference of two means.

Formula:

Pooled standard deviation

`s_p = \sqrt{\displaystyle((n_1-1)\sigma_1^2 + (n_2-1)\sigma_2^2 )/(n_1 + n_2 - 2)}`

`t_(stat) = \displaystyle\frac{\mu_1-\mu_2}{s_p\sqrt{(1)/(n_1)+(1)/(n_2)}}`

`\text{Degree of freedom} = n_1 + n_2 - 2`

Putting all the values we get:

`s_p = \sqrt{\displaystyle((7-1)(2)^2 + (9-1)(1.9)^2 )/(7 + 9 - 2)} = √(3.7771) =1.94`

`t_(stat) = \displaystyle\frac{7-4}{1.94\sqrt{(1)/(7)+(1)/(9)}} = 3.068`

`\text{Degree of freedom} = 7 + 9 - 2 = 14`