Researchers wanted to determine if carpeted rooms contained more bacteria than uncarpeted rooms. To determine the amount of bacteria in a room, researchers pumped the air from the room over a Petri dish at a rate of 1 cubic foot per minute for eight carpeted rooms and eight uncarpeted rooms. Colonies of bacteria were allowed to form in the 16 Petri dishes. The results were collected. A normal probability plot and box plot indicate the data are approximately normally distributed with no outliers. The data is as follows in bacteria per cubic foot:
Carpeted: 11.8, 10.8, 8.2, 10.1, 7.1, 14.6, 13.0, 14.0
Uncarpeted: 12.1, 12.0, 8.3, 11.1, 3.8, 10.1, 7.2, 13.7
Determine using the appropriate hypothesis testing technique if carpeted rooms have more bacteria than uncarpeted rooms at the .05 level of significance.© BrainMass Inc. brainmass.com October 25, 2018, 7:40 am ad1c9bdddf
Null Hypothesis: The mean amount of bacteria per cubic foot in carpeted rooms is lower than or equal to that in uncarpeted rooms. H0: u1 <= u2
Alternate Hypothesis: The mean amount of bacteria per cubic foot in carpeted rooms is greater than that in uncarpeted rooms. H1: u1 > u2
Type I and II errors and Confidence interval
1. You have been asked to evaluate if a particular coin is fair or not. You have decided to use the following test:
Accept that the coin is fair if in 30 tosses the coin gives between 11 and 19 heads (inclusive); reject the hypothesis of fairness otherwise.
Compute the Type I error rate of this test. Interpret, in plain words, what the computed number would mean.
Compute the power (Type II error) of this test at p=.3, .49, .51, and .7. Interpret what the computed numbers mean. In addition, comment on any interesting patterns you found in these numbers. Then explain what is the cause of the patterns you discovered.
2. The time till first failure of a brand of HD plasma tvs is advertised to be more than 8 years. Suppose you sample 15 tvs of this type, keep track of them, and accept the advertised claim if the mean time to the first failure is larger than 8.5 years.
Plot the type I error probability and the power function of this particular test.
3. A t-statistic for testing H0: μ=3.5 is to be computed based on 20 observations with a mean of 4 and a standard deviation of 1.
Then, a 21st observation was collected and this new observation was 10. Recompute the t-statistic when all 21 observations are used.
Comment on what you find.
4. In 8 hospital rooms that are carpeted, and another 8 that are uncarpeted, bacteria per cubic ft. were counted, and the data are as follows:
Carpeted rooms: 11.8, 8.2, 7.1, 13, 10.8, 10.1, 14.6, 14
Uncarpeted rooms: 12.1, 8.3, 3.8, 7.2, 12, 11.1, 10.1, 13.7
Compute a nominal 90% confidence interval for the difference in mean bacterial count per cubic ft. in carpeted and uncarpeted hospital rooms. Discuss the pros and cons of each type of confidence interval for this particular application. Discuss what assumptions you would be concerned about and whether you can test them, if you have any doubts.