Why do zebras have stripes? One hypothesis is that stripes help keep biting flies away. Trinity wants to test this hypothesis with an experiment. She will use 15 horses as the subjects in her...

Why do zebras have stripes? One hypothesis is that stripes help keep biting flies away. Trinity wants to test this hypothesis with an experiment. She will use 15 horses as the subjects in her experiment, and assign them to 3 treatments, as follows:

1. 5 horses will wear a fabric coat that is printed with zebra stripes, as shown above


2. 5 horses will wear nothing


3. 5 horses will wear a fabric coat that is printed with a solid grey colour

Trinity will record a video of each horse for 1 hour. She will use the video to determine the number of biting flies that land on the horse's back.

a) What types of experimental group do each of (i), (ii), and (iii) represent?

Choose from:

• Main experimental treatment group


• Classical control


• Positive control


• Negative control

b) Why is it important for Trinity to include group (iii) in her study? Provide a brief explanation. Hint: you can describe potential scenarios for results to help explain why group (iii) is needed.

c) Can you suggestONE
potential confounding variable that might be important for Trinity's experiment?

d) If you were designing this experiment, how would you account for the variable you identified in (c)? Explain briefly what methods you would recommend to ensure that the results of the experiment are sound.

e) Could this study be done using a within-subjects experimental design? Why or why not?