are sheets worth the money? sleep on it… katharine chen megan spillane richard winn
TRANSCRIPT
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Are Sheets Worth the Money?Sleep On It…
Katharine Chen
Megan Spillane
Richard Winn
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Purpose
• People want to have a comfortable bed, but there are countless varieties of sheets, bedding etc.
• Since we’re all struggling college students looking to save a buck or two, we wanted to see if spending more on sheets is really worthwhile.
• She thinks so
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• More expensive sheet costs $6.99 per yard• Cheaper sheet costs $5.99 per yard
If you’re making a king size bed, choosing the cheaper sheet saves a consumer just under $15.
For our twin extra longs, it’s still over $8.
That’s a lot of money!
Purpose, Continued
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So is there really a difference???
Which sheet do college students prefer? The cheaper, 230-thread count sateen sheet, or the more expensive 250-thread count Egyptian sheet?
Can college students even feel a difference between the two sheets?
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Pre-test beliefs
• We believe that college students will indeed be able to feel a difference.
• We suspect that 80% of college students will prefer the more
expensive sheet. • Power hypothesis:
P=.8
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Null Hypothesis
• College students will be equally likely to prefer the more expensive sheet and the cheaper sheet.
• Let p equal the percentage of college students who prefer the more expensive sheet.
• Null Hypothesis: p = 0.5
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Alternative Hypothesis
• Our alternate hypothesis is that the college students who have a preference will favor the more expensive sheet.
• p > 0.5
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Procedure
• We gave the subject two sheet samples and ask them two questions:
1. Can you feel a difference? And if so…
2. Which do you prefer?
• Note their preference
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It’s Double-Blind!
• We had two sets of sheets, and in each set one sheet was marked. (determined randomly)
• The tester was randomly given one of these sets to give each participant by the “DISTRIBUTOR”…
• So, the tester did not know which sheet was which, and recorded simply “marked” or “unmarked”
• We translated this “coded message” into data we can all understand!
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Data
• Wow! This is our data!
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Results
• We were wrong
• A majority of college students did in fact prefer one sheet over the other, but, contrary to our pre-test beliefs, they preferred the cheaper sheet over the more expensive sheet
• “It was softer,” they said (of the cheaper sheet)… “I like the way it smells!”
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Result Data
• Of the 51 students we sampled, 48 felt a difference, 3 could not feel a difference.
• 89.6% of the opinionated subjects preferred the cheaper sheet.
• Only 5 students preferred the more expensive sheet!!
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Power and Significance
• We set up a significance level of .05, leaving only 5% chance of Type I error.
• This set our critical value at .618, or 30 out of 48 participants. Needless to say, we did not meet this requirement.
• Our power, calculated using P=.8, was 99.9%. This leaves only .1% chance of Type II error. The power is so large because the sample size is almost 50.
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Binomial and Power Distributions
Are we kidding? Sadly, the answer is no. Our result was barely on the chart.
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Confounding Factors
• Price and thread count are not the only factors influencing the feel of the sheets.
• The cheaper sheet was a sateen weave, and as a result it may have had a softer feel and finish even though it may be of a lesser thread count and durability.
• Since sateen must be thicker because of its lack of durability, it may be softer but lack the “lightness” and “coolness” that is desirable in the sheet market.
• Further, more accurate studies could include more weaves of sheets, and allow participants to curl up in a bed.
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Wow. They’re not done yet…
• We decided to conduct a follow-up test (since we are clearly great at predictions) doing everything the same, except THIS time:
• We told the subjects which sheet was more expensive, and which sheet was cheaper.
• We’re getting psychological.
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Would this make a difference?
YES!
I hope they’re done soon…
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Is this the last slide?
• 27% of the INFORMED subjects preferred the more expensive sheet
• 73% preferred the cheaper sheet
• Whereas 89% of the UNINFORMED subjects preferred the cheaper sheet.
• Clearly, 27% is much less than our original 80% power hypothesis, but it is much closer!
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Applause…Next please. Please??
Yellow indicates Group 1. Blue indicates Group 2.
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• We compared the difference between the means of the two samples.
• The z-score corresponding to the difference between the two means is 2.12.
• This is found by the following formula:
X1 - X2
Z=
S12/N1 + S2
2/N2
No, seriously, aren’t you done?
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I really hope they sit down soon…
• Since this Z-score is larger than the Z-score corresponding to a significance level of .05 (1.65), we can say with 95% confidence that the difference between the two samples is not due to pure luck.
• This goes to show that people are superficial and can be influenced by price. They think the more expensive it is, better it is.
• Go for the cheaper sheets. Spend your money on other heavily advertised products!!!
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Thank God…
THE END