Presentation on theme: "Are Sheets Worth the Money? Sleep On It… Katharine Chen Megan Spillane Richard Winn."— Presentation transcript:
Are Sheets Worth the Money? Sleep On It… Katharine Chen Megan Spillane Richard Winn
Purpose People want to have a comfortable bed, but there are countless varieties of sheets, bedding etc. Since were 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
More expensive sheet costs $6.99 per yard Cheaper sheet costs $5.99 per yard If youre making a king size bed, choosing the cheaper sheet saves a consumer just under $15. For our twin extra longs, its still over $8. Thats a lot of money! Purpose, Continued
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?
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
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
Alternative Hypothesis Our alternate hypothesis is that the college students who have a preference will favor the more expensive sheet. p > 0.5
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
Its 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!
Data Wow! This is our data!
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!
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!!
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.
Binomial and Power Distributions Are we kidding? Sadly, the answer is no. Our result was barely on the chart.
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.
Wow. Theyre 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. Were getting psychological.
Would this make a difference? YES! I hope theyre done soon…
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!
Applause…Next please. Please?? Yellow indicates Group 1. Blue indicates Group 2.
We compared the difference between the means of the two samples. The z-score corresponding to the difference between the two means is This is found by the following formula: X 1 - X 2 Z= S 1 2 /N 1 + S 2 2 /N 2 No, seriously, arent you done?
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!!!