In a Stroop test, participants are presented with a list of words, with each word displayed in a color of ink. The participant’s task is to say out loud the color of the ink in which the word is printed.
Data
The task has two conditions: a congruent words condition, and an incongruent words condition. In each case the time it takes to name the ink colors in equally-sized lists is measured. Each participant will go through and record a time from each condition.
- In the congruent words condition, the words being displayed are color words whose names match the colors in which they are printed.
- In the incongruent words condition, the words displayed are color words whose names do not match the colors in which they are printed.
Dependency
The independent variable in this data set is congruent data because it stands alone and isn't changed by the other variables. The incongruent data set is our dependent variable because it could change depending on several factors, in this case it’s the time it takes the student to answer the question.
Hypothesis
H0 = The two samples t-statistic do not statistically differ at an alpha of .05
HA = The two samples t-statistic do statistically differ at an alpha of .05
HA = The two samples t-statistic do statistically differ at an alpha of .05
Statistical Test
Because the mean difference might be due to expected variability, we need to do a T-Test to find out if the difference is significant. I will perform a dependent paired, two-sample for mean T-Test.
- Dependent: I chose dependent because there is only one sample that has been tested twice
- Paired: I chose paired because our participants were measured at two time points (so each individual has two measurements).
Exploratory Data Analysis
I will start by generating some basic descriptive statistics to keep in mind as a baseline for comparison of future results. At least one measure of central tendency and at least one measure of variability.
- Congruent Mean: 14.051125
- Incongruent Mean: 22.0159166667
- Congruent Variance: 12.66902907
- Incongruent Variance: 23.01175704
On this scatter, because the vertical range is larger in range but shorter in length, the true relationship of the data exists on a steeper incline than shown.
When plotting this area graph, all participants took longer to answer when tested on the incongruent data set.
T-Test
- Alpha: 0.05
- T-Critical: 1.714
- T-statistic: -8.020706944
- P-Value (2-tail): 0.00000004103000587
Conclusion
Getting a p-value of 0.000000041 means that if we were to repeat our experiment many, many times (each time with 24 random participants and compute the sample mean) then 0.000000041 times out of 100 we would expect to see a sample mean greater than 22.015.
I will reject the null hypothesis.
The results did match up with my expectations. My personal experiences were that I took longer and made more mistakes when I trained on the incongruent data set
I suspect the incongruent data set is harder to interpret because the brain uses separate modules for processing color and for processing writing. I also wonder if the incongruent results would be similar to any other two signal mixes, for example, if someone was to verbally say “blue” at the same time you read the word “red”.
An alternative test that I believe would result in a similar effect would be to measure the accuracy of participants brushing their teeth with their non-dominant hand. I am right handed and I noticed that when I try to brush my teeth with my left hand it takes more mental effort.