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 2. Charmin Ultra 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. Scott 1-ply 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 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 Trial 1 – weight sustained Charmin 45g (10 nickels) 49.5g (11 nickels) Seventh Generation 40.5g (9 nickels) 31.5g (7 nickels) Cottonelle 54g (12 nickels) Scott 27g (6 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 higher-priced 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!