A health educator wants to evaluate the effect of a dental film on the frequency with which children brush their teeth. A random selection of 8 children are used for the experiment. First, a baseline of the number of times the children brush their teeth over a month's period is established. Next, the children are shown the dental film and again the number of teeth brushings are recorded for a month. The following data are recorded. Assume there is a real effect and estimate the size of effect, using Cohens d. = _________.
A) 1.10
B) 0.03
C) 1.11
D) 0.02

Question

A health educator wants to evaluate the effect of a dental film on the frequency with which children brush their teeth. A random selection of 8 children are used for the experiment. First, a baseline of the number of times the children brush their teeth over a month's period is established. Next, the children are shown the dental film and again the number of teeth brushings are recorded for a month. The following data are recorded.  Assume there is a real effect and estimate the size of effect, using Cohens d. = _________.
A) 1.10 
B) 0.03 
C) 1.11 
D) 0.02

Quizplus · Accepted Answer

To calculate Cohen's d, we first need to find the mean difference between the number of teeth brushings before and after showing the dental film.

Mean difference = (13+15+5+8+6+11+9+12)/8 - (8+10+3+5+3+7+6+7)/8 
= 9 - 5.375 
= 3.625

Next, we need to find the pooled standard deviation, which takes into account the variability in both the pre- and post-intervention measurements.

Pooled standard deviation = sqrt[((7-1)(2.774^2) + (7-1)(2.266^2))/(2(7))] 
= 2.521

Finally, we can calculate Cohen's d by dividing the mean difference by the pooled standard deviation:

Cohen's d = 3.625/2.521 
= 1.44

Since Cohen's d is greater than 1.0, the effect size is considered large.

Therefore, the best choice is (C).

A Health Educator Wants to Evaluate the Effect of a Dental