This study aims to test the hypothesis that shaving hair causes it to grow back thicker. It will involve 150 volunteers divided into two age groups. Volunteers will be randomly assigned to shave their arms and legs once, shave twice, or not shave at all. Hair thickness will be measured before and after using cluster samples. Blocking volunteers by age controls for natural differences in hair growth. The results will show if shaving leads to higher hair concentration when it regrows. Possible errors include volunteers not properly following the shaving treatment.

1. If you shave hair, it grows
back thicker
Allie Wendell

2. Hypothesis
There will be a higher concentration of hair in any given area as it
grows back after being shaved.

3. Variables
Explanatory variable: number of shaves
Responding variable: thickness of hair after shave (hairs/square inch)

4. Selecting Sample Size
150 volunteers total
75 volunteers aged 30 or younger
75 volunteers over the age of 30

5. Treatment
The 150 volunteers are grouped by age—subjects 30 or younger in one experiment
and subjects over the age of 30 in a different experiment sine age may influence
hair growth. Before the experiment begins, the average number of hairs per square
inch on each person will be calculated using data from both arms and legs as a
sample. The 75 volunteers in each age group will be randomly assigned to 3
different treatments—shaving body hair once, not shaving at all, and shaving twice
on two separate occasions. The control group (not shaving at all) accounts for the
possibility that hair grows thicker over time without shaving. Since counting all
hairs on the arms and legs of every subject would be unrealistic, cluster samples
could be used to compute an average number of hairs per square inch for each
volunteer.

6. volunteers
30 and younger
Older than 30
Shave arms and legs once
Shave once, wait for hair to
grow back, shave again
Shave arms and legs once
Shave once, wait for hair to
grow back, shave again
RA
RA
Don’t shave
Don’t shave
Compare results
Compare results

7. Experimental Design
The blocking of the subjects by age helps to ensure that the results are not skewed
by a consistent difference in hair growth between the ages. For example, if older
people grow less hair naturally, this could change the average results calculated
amongst the younger group if blocking was not used. This experiment could not use
blinding techniques because the subjects clearly know whether they have been
instructed to shave their arms, and there is no alternative that can be disguised as
the same treatment. The more the experiment is replicated with more
subjects/larger sample sizes, the more accuracy can be assured if the results
remain consistent through each experiment.

8. Calculating and Analyzing Results
After the study, the same cluster method would be used to calculate
the average number of hairs per square inch for each subject in the
experiment. The beginning and end results would be compared. If the
hypothesis is correct, the average concentration of hairs will be higher
after the shaving treatment.

9. Concerns/Possible Sources of Error
Since the treatment can’t be closely supervised, people might forget or
neglect to perform the treatment on their own, which could skew the
results.