Chi-Square and t-Tests


Chi-Square and t-Tests in SPSS


Having grown tired of working with rats, a group of ambitious researchers genetically engineered super-hamsters.  They discovered a way to create hamsters in all colors of the rainbow.  Taking a subsample of 40 colorful hamsters (red, yellow, green, and blue), the researchers randomly assigned the hamsters to a treatment or control group.  The treatment group had a bioluminescence gene added to their DNA sequence, which caused them to glow in the dark.  The researchers hypothesized that this would affect the hamster’s self-esteem, such that the glowing hamsters would exhibit more self-confidence due to their fantastic appearance, and thus would complete a maze faster than hamsters who could not bioluminesce. Prior to the “big race”, the researchers gave the hamsters some practice runs in the maze (round1 and round2) where scores represent how long it took the hamsters to successfully complete the running of the maze.  The data file “hamsterdata.sav” contains 7 variables:

ID – identification numbers assigned to the hamsters

Treat – Treatment = 1/Control = 0 assignment

Color – red, yellow, green, or blue

Weight – Hamster’s weight in ounces

Time – time to complete the maze in the “big race”

round1 – time to complete the maze in the first practice run

round2 – time to complete the maze in the second practice run

1.     Your first hypothesis has to do with whether hamsters of each color occur with equal frequency.  Test this hypothesis using a Univariate Chi-Square test to determine if certain colors are more common than others. What do the results indicate? Report the results in APA style and also interpret the results in terms of what this means for color frequencies.


2.      When the researchers were deciding which hamsters to give the special bioluminescent gene to, did they discriminate based on color?  If they did, there should be a significant association between treat and color.  Test this hypothesis by conducting a Bivariate Chi-Square test. Was there a significant association? Report the results in APA style and also interpret the results in terms of the relationship between the two variables.


3.      Your next research question involves the variable weight.  You know that in the population, the average hamster weight (µ) = 4 ounces. Test the hypothesis that the average weight in this sample of hamsters is different than the population average of 4 ounces using a Single Sample t-Test.  What do you conclude? Report the results in APA style. Are these hamsters generally heavier, lighter, or the same weight as average-sized hamsters?


4.      Does the addition of the bioluminescent gene really increase hamster self-esteem, thus making them complete the maze faster?  Using treat as your grouping variable, conduct an Independent Samples t-Test on time.  Report the results in APA style. What do you conclude about the effect of the gene on time?


Finally, did the practice runs help the hamsters finish the maze faster?  Conduct a Dependent (Paired) Samples t-Test on round1 and round2 scores to determine if the hamsters ran the maze faster in the second practice round.  Report the results in APA style. What do you conclude about the practice runs?