Question

Experimenter bias refers to the phenomenon that data tends to comes out in the desired direction even for the most conscientious experimenters. A social psychologist wants to confirm this phenomenon. In a study, the psychologist tells a sample of students that they will be experimenters in study that investigates the impact of caffeine on cognition. The experimenters are told that all subjects will be given caffeine an hour before solving arithmetic problems. However, half of the experimenters are told that caffeine will lead to better performance and the other half are told nothing. The experimenters are then asked to grade the arithmetic problems. What can the psychologist conclude with an α of 0.05? Below are the grades that they gave.

told nothing	leads to better performance
18 15 21 12 17 14 20 24	12 14 13 8 14 17 20 10

a) What is the appropriate test statistic?
---Select--- na z-test One-Sample t-test Independent-Samples t-test Related-Samples t-test

b)
Condition 1:
---Select--- told nothing told caffeine leads to better performance grades the phenomenon experimenter bias
Condition 2:
---Select--- told nothing told caffeine leads to better performance grades the phenomenon experimenter bias

c) Compute the appropriate test statistic(s) to make a decision about H₀.
(Hint: Make sure to write down the null and alternative hypotheses to help solve the problem.)
critical value =  ; test statistic =  
Decision:  ---Select--- Reject H0 Fail to reject H0

d) If appropriate, compute the CI. If not appropriate, input "na" for both spaces below.
[  ,  ]

e) Compute the corresponding effect size(s) and indicate magnitude(s).
If not appropriate, input and/or select "na" below.
d =  ;  ---Select--- na trivial effect small effect medium effect large effect
r² =  ;  ---Select--- na trivial effect small effect medium effect large effect

f) Make an interpretation based on the results.

Experimenters that were told nothing gave significantly higher grades than experimenters that expected a good performance.

Experimenters that expected a good performance gave significantly higher grades than experimenters that were told nothing.     

There was no significant grade difference between experimenters that expected a good performance and those that were told nothing.

Answer 1

a) Correct answer: t-test related samples

b) told nothing told caffeine leads to better performance grades the phenomenon experimenter bias

c)
H0: caffeine will not lead to better performance and the other half are told nothing

H1: caffeine will lead to better performance and the other half are told nothing

From the given data

told	leads to better
nothing	performance	Difference
18	12	6
15	14	1
21	13	8
12	8	4
17	14	3
14	17	-3
20	20	0
24	10	14
	Total:	33

Critical t: 1.8946

Here t value is > t critical value so we reject H0

Thus we conclude that caffeine will lead to better performance and the other half are told nothing

d) The 95% confidence interval for difference of populatin mean is

e)

e)

f) correct answer: Experimenters that expected a good performance gave significantly higher grades than experimenters that were told nothing.