Statistics for The Behavioral Scie...

10th Edition
Frederick J Gravetter + 1 other
ISBN: 9781305504912



Statistics for The Behavioral Scie...

10th Edition
Frederick J Gravetter + 1 other
ISBN: 9781305504912
Textbook Problem

Two separate samples receive different treatments. After treatment, the first sample has n = 9 with S S = 462 , and the second has n = 7 with S S = 420 .

a. Compute the pooled variance for the two samples.

b. Calculate the estimated standard error for the sample mean difference.

c. If the sample mean difference is 10 points, is this enough to reject the null hypothesis using a two-tailed test with α = .05 ?

To determine

Sample variances, Pooled variance, standard error of mean difference, also we need to take decision that a difference of mean is significant or not.


Here we have given with different two SS and we need to find variance as well as pooled variance so here we will use general formula so that we can use for any two different sample size.

Here we need to find that the standard error of mean difference that will be described that how far is the distance of the two means of the sample from the population difference. Also we have testing in the part c there will be decide that whether true difference is 10 or not basis of sample data we have.


Here we are provided with two SS that is SS1=462 and SS2= 420, also for

n1=9, n2=7

Formula used:

For one sample of size n, we have below formulas

Mean= x¯ = 1ni=1nxi

SS= i=1n(xix¯)2

Variance= 1n1i=1n(xix¯)2

If there are two samples of sizes n1and n2 we have the following formula for pooled SD,

Sp=Pooled Variance


S12=sample variance of first sample

S22=sample variance of second sample


Se=standard error of the mean,



  1. Here
  2. n1=9,n2=7 So now


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