For a repeated-measures study comparing two treatments with a sample of [tex]n=9[/tex] participants, the difference scores have a mean of [tex]M_D=4.9[/tex] with [tex]SS=72[/tex]. What is the estimated standard error and [tex]t[/tex] value for this study?

A. [tex]S_{MD}=1[/tex] and [tex]t=4.9[/tex]

B. [tex]S_{MD}=1.5[/tex] and [tex]t=3.26[/tex]

C. [tex]S_{MD}=9[/tex] and [tex]t=0.54[/tex]

D. [tex]S_{MD}=3[/tex] and [tex]t=1.63[/tex]



Answer :

To solve this question, we need to calculate the estimated standard error [tex]\( S_{M_D} \)[/tex] and the t value step-by-step. Let's start with the information given:

- Sample size, [tex]\( n = 9 \)[/tex]
- Mean of the difference scores, [tex]\( M_D = 4.9 \)[/tex]
- Sum of squares of the difference scores, [tex]\( SS = 72 \)[/tex]

1. Calculate the variance of the difference scores:
[tex]\[ \text{Variance}_D = \frac{SS}{n - 1} \][/tex]
Here, [tex]\( n - 1 = 9 - 1 = 8 \)[/tex],
[tex]\[ \text{Variance}_D = \frac{72}{8} = 9 \][/tex]

2. Calculate the standard deviation of the difference scores:
[tex]\[ \text{Standard Deviation}_D = \sqrt{\text{Variance}_D} \][/tex]
[tex]\[ \text{Standard Deviation}_D = \sqrt{9} = 3 \][/tex]

3. Calculate the estimated standard error [tex]\( S_{M_D} \)[/tex]:
[tex]\[ S_{M_D} = \frac{\text{Standard Deviation}_D}{\sqrt{n}} \][/tex]
Here, [tex]\( \sqrt{n} = \sqrt{9} = 3 \)[/tex],
[tex]\[ S_{M_D} = \frac{3}{3} = 1 \][/tex]

4. Calculate the t value:
[tex]\[ t = \frac{M_D}{S_{M_D}} \][/tex]
[tex]\[ t = \frac{4.9}{1} = 4.9 \][/tex]

Therefore, the estimated standard error [tex]\( S_{M_D} \)[/tex] is 1 and the t value is 4.9. So the correct answers are:

[tex]\[ S_{M_D} = 1 \][/tex] and [tex]\[ t = 4.9 \][/tex]