The Great Toilet Paper
Experiment
By Robert Feasley
and Allie O’Hora
AP Statistics period 1
Problem Statement
We want to find out: which brand of toilet
paper is the strongest?
In other words, is the price of a certain brand of
toilet paper correlated with its strength and
quality?
The Goods
1. Seventh Generation Organic
4-pack: $3.99 at Whole Foods
2. Charmin Ultra
4-pack: $4.49 at Giant Food
The Goods, continued
3. Cottonelle Double
with Ripples
4-pack: $3.79 at Giant Food
4. Scott 1-ply
4-pack: $2.49 at Giant Food
Hypothesis
Because we are testing the correlation
between price and strength, we hypothesize that
the most expensive brand, Charmin Ultra, will
perform the best in a strength test.
H0: Dampened Charmin Ultra toilet paper will
sustain larger amounts of weight than the other
brands under the same conditions.
HA: Another brand of toilet paper, when dampened,
will sustain a larger amount of weight than
Charmin Ultra.
Experimental Design
 We bought two rolls of each brand of toilet paper. We assume
that these four rolls can be considered a random sample of all
rolls manufactured by that brand.
 We then unrolled 20 feet of used a random number table to
select values, 0-9, to determine which part of that 20-foot section
we would use for our sample. For example, a value of “9” meant
that we would use feet 18 and 19 as the selected 2 foot section
from the 20 feet of toilet paper. In this way, we randomized the
portion of the paper used as well as the selection of the roll itself.
We did this for each roll, meaning that for each brand tested we
had two trials.
 To minimize any sources of error, we also standardized the
weights we used (nickels), the amount of water we applied to
each (2 tablespoons), the location and spread of the water on the
paper, and the way in which the experiment was set up.
Process
1.
2.
3.
4.
5.
6.
Measure two feet of toilet paper
determined by randomized experimental
design (see previous slide)
Stretch length of toilet paper across two
chairs, supports or similar so that 1 foot is
suspended without any support. Secure
with two equally sized weights
Apply 2 tablespoons of water in a circular
motion so that the center of the paper is
uniformly soaked.
Drop a nickel onto the center of the paper
from a height of about 2 inches.
Repeat step four until the paper breaks.
Count the number of nickels used and
calculate the weight that the toilet paper
withstood. Record data.
Repeat as necessary – two trials for each
brand, four trials in total.
Assumptions/Constants
 The weight of 1 nickel is 4.5 grams.
 We assume each roll of toilet paper can be
considered a SRS of their brand and that each
2-foot section is a random sample of the roll
itself.
 There is no reason to believe that the rolls of
toilet paper or the separate sections from each
roll are not independent from one another.
 Though sample size is small, we will perform the
sample anyway, carefully maintaining conditions
to ensure that we do not introduce any bias or
confounding.
Data/Results
Brand
Charmin
Seventh
Generation
Cottonelle
Scott
Trial 1 – weight Trial 2 – weight
sustained
sustained
45g (10 nickels) 49.5g (11
nickels)
40.5g (9 nickels) 31.5g (7 nickels)
49.5g (11
nickels)
27g (6 nickels)
54g (12 nickels)
18g (4 nickels)
Conclusion and Application
 We concluded that Cottonelle brand toilet paper is the
strongest. Our hypothesis – that price is correlated with
strength – was somewhat correct in that the higherpriced toilet papers (Cottonelle, Charmin) performed
better. However, our H0 was ultimately incorrect;
Cottonelle outperformed Charmin toilet paper in the
tests.
 We noted that two-ply toilet papers, which are also the
more expensive varieties, supported significantly more
weight in our tests than did the one-ply brands.
 In terms of application, if you are looking for a strong,
sturdy toilet paper, you should consider shelling out the
extra cash for a two-ply brand like Cottonelle or Charmin.
Possible Confounding Factors/
Sources of Error
A few possible sources of error might
include:
Human error: unequal distance/force of nickel
drop, etc.
Inconsistencies in the quality of the toilet paper
Inherent differences in the papers themselves,
i.e. 1-ply vs. 2-ply
THE END!