Question

In a study of memory process, rats were first presented with a fear-inducing stimulus on a learning task as soon as they stepped across a line in a test chamber. Afterwards, the rats were divided and given electrical stimulation either 50 or 150 milliseconds after crossing the line. In addition, the rats differed in terms of the area in which the stimulation electrodes were implanted in their brains (Neutral Area, Area A, or Area B). Researchers were interested in the time it took the animals to re-cross the line on a subsequent learning task. The idea is that stimulation of certain areas in the brain would interfere with memory and hence delay learning to avoid the line on the subsequent learning task. The data on time to re-cross the line are below. What can be concluded with an α of 0.05?

                     Area

Time	neutral	A	B
50	26 31 29 41 21	12 19 25 16 15	24 18 19 29 24
150	26 29 24 18 33	26 31 38 30 24	27 20 29 29 22

Time: test statistic =

Area: test statistic =

Interaction: test statistic =

Compute the corresponding effect size(s) and indicate magnitude(s).
Time: η² =   ;  ---Select--- na trivial effect small effect medium effect large effect  
Area: η² =   ;  ---Select--- na trivial effect small effect medium effect large effect  
Interaction: η² =   ;  ---Select--- na trivial effect small effect medium effect large effect  

Answer 1

SPSS used

In a study of memory process, rats were first presented with a fear-inducing stimulus on a learning task as soon as they stepped across a line in a test chamber. Afterwards, the rats were divided and given electrical stimulation either 50 or 150 milliseconds after crossing the line. In addition, the rats differed in terms of the area in which the stimulation electrodes were implanted in their brains (Neutral Area, Area A, or Area B). Researchers were interested in the time it took the animals to re-cross the line on a subsequent learning task. The idea is that stimulation of certain areas in the brain would interfere with memory and hence delay learning to avoid the line on the subsequent learning task. The data on time to re-cross the line are below. What can be concluded with an α of 0.05?

                     Area

Time	neutral	A	B
50	26 31 29 41 21	12 19 25 16 15	24 18 19 29 24
150	26 29 24 18 33	26 31 38 30 24	27 20 29 29 22

Time: test statistic =3.675, Not significant

Area: test statistic =1.786, Not significant

Interaction: test statistic =5.521, Significant

Compute the corresponding effect size(s) and indicate magnitude(s).
Time: η² = 0.13  ;   trivial effect
Area: η² = 0.13  ;   trivial effect
Interaction: η² =0.32   ;   small effect

SPSS syntax:

UNIANOVA score BY time area

/METHOD=SSTYPE(3)

/INTERCEPT=INCLUDE

/PRINT ETASQ DESCRIPTIVE

/CRITERIA=ALPHA(.05)

/DESIGN=time area time*area.

SPSS output:

Descriptive Statistics
Dependent Variable:   score
time	area	Mean	Std. Deviation	N
50	neutral	29.60	7.403	5
	A	17.40	4.930	5
	B	22.80	4.438	5
	Total	23.27	7.411	15
150	neutral	26.00	5.612	5
	A	29.80	5.404	5
	B	25.40	4.159	5
	Total	27.07	5.133	15
Total	neutral	27.80	6.477	10
	A	23.60	8.154	10
	B	24.10	4.280	10
	Total	25.17	6.555	30

Tests of Between-Subjects Effects
Dependent Variable:   score
Source	Type III Sum of Squares	df	Mean Square	F	Sig.	Partial Eta Squared
Corrected Model	538.967a	5	107.793	3.658	.013	.432
Intercept	19000.833	1	19000.833	644.825	.000	.964
time	108.300	1	108.300	3.675	.067	.133
area	105.267	2	52.633	1.786	.189	.130
time * area	325.400	2	162.700	5.521	.011	.315
Error	707.200	24	29.467
Total	20247.000	30
Corrected Total	1246.167	29
a. R Squared = .432 (Adjusted R Squared = .314)