25. A researcher studied the effect of feedback on estima- tion of length. Two s

Question

25. A researcher studied the effect of feedback on estima- tion of length. Two samples of participants were given practice estimating the lengths of lines drawn by the researcher on a chalkboard. One group received no feedback about the accuracy of the estimates. The second group received feedback ("too long," "too short") for accuracy. Then everyone was tested for accuracy of length estimation. The amount of error, in inches, was measured for all participants. The follow- ing table gives the data. No Feedback Feedback 0 a. Does feedback have a significant effect on accu racy? Use a two-tailed test with a0S b. Calculate the estimated d and r (percentage of variance accounted for) to measure the effect size for this study

Explanation / Answer

QUestion 25

For feedback :

sample mean x1 = 6

sample standard deviation s1 = 1.4142

sample mean x2 = 3

sample standard deviation s2 = 1.6330

H0 : 1 = 2

Ha : 1 2

Pooled standard deviation sp = sqrt [(n1 - 1)s12 + (n2 - 1)s22 }/(n1 + n2 -2)] = sqrt [(3 * 2 + 3 * 2.667)/6] = 1.5275

Test statistic

t = (x1 - x2)/ [sp * sqrt [1/n1 + 1/n2] = (6 - 3)/ sqrt [7 * (1/3 + 1/3)] = 3/ 2.1602 = 1.3887

Here for dF = 6 and alpha = 0.05 and two tailed test

tcritical = 2.447

so here t <  tcritical so we fail to reject the null hypothesis and can say that there is no significant impact of feedback.

(b) Estimated d = (x1 - x2)/ sp = (6 - 3)/1.5275 = 1.964

so here the estimated cohen d is so much higher and that is very large effect size here.

r2 = t2/(n-2 + t2)

r2 = 1.38872/ (3 - 2 + 1.38872) = 0.6585

so here the the effect size is also very good here.

Related Questions

Navigate

• Browse (All)
• Browse 2
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.