A clinical psychologist wished to compare three methods for reducing hostility levels in university students using a certain psychological test (HLT). High scores on this test were taken to indicate great hostility, and 11 students who got high and nearly equal scores were used in the experiment. Five were selected at random from among the 11 students and treated by method A, three were taken at random from the remaining six students and treated by method B, and the other three students were treated by method C. All treatments continued throughout a semester, when the HLT test was given again. The results are shown in the table.
Method | Scores on the HLT Test | ||||
A | 72 | 82 | 76 | 67 | 78 |
B | 54 | 75 | 69 | ||
C | 78 | 94 | 89 |
Let μA and μB, respectively, denote the mean scores at the end of the semester for the populations of extremely hostile students who were treated throughout that semester by method A and method B.
(a) Find a 95% confidence interval for
μA. (Round your answers to two
decimal places.)
(b) Find a 95% confidence interval for μB.
(Round your answers to two decimal places.)
(c) Find a 95% confidence interval for (μA −
μB). (Round your answers to two decimal
places.)
(d) Is it correct to claim that the confidence intervals found in
parts (a), (b), and (c) are jointly valid?
A clinical psychologist wished to compare three methods for reducing hostility levels in university students using...
A clinical psychologist wished to compare three methods for reducing hostility levels in university students using a certain psychological test (HLT). High scores on this test were taken to indicate great hostility, and 11 students who got high and nearly equal scores were used in the experiment. Five were selected at random from among the 11 students and treated by method A, three were taken at random from the remaining six students and treated by method B, and the other...
A consumer preference study compares the effects of three different bottle designs (A, B, and C) on sales of a popular fabric softener. A completely randomized design is employed. Specifically, 15 supermarkets of equal sales potential are selected, and 5 of these supermarkets are randomly assigned to each bottle design. The number of bottles sold in 24 hours at each supermarket is recorded. The data obtained are displayed in the following table. Bottle Design Study Data A B C 16...
A manager wants to compare the mean time required to build a product using two different assembly methods, A and B. The time per unit was recorded for independent random samples from each method. The results are below. Assuming that the variances for the two populations are equal, use this data to form a 99% confidence interval for the true difference (μA−μB)(μA−μB) between the mean times for the two methods. Do not round intermediate calculations. Enter your final answers as...
(4)Five hundred students from a local high school took a college entrance examination. Historical data from the school record show that the standard deviation of test scores is 40. A random sample of thirty- six students is taken from the entire population of 500 students. The mean test score for the sample is three hundred eighty. Find (a) 95% confidence interval for the unknown population mean test score. (b) 95% confidence interval for the unknown population mean test score if...
Suppose the preliteracy scores of three-year-old students in the United States are normally distributed. Shelia, a preschool teacher, wants to estimate the mean score on preliteracy tests for the population of three-year-olds. She draws a simple random sample of 20 students from her class of three-year-olds and records their preliteracy scores (in points). 74, 79, 83, 85, 88, 90, 94, 95, 95, 97,99, 99, 100, 103, 105, 105, 106, 107, 107, 108 Click to download the data in your preferred...
Suppose the preliteracy scores of three-year-old students in the United States are normally distributed. Shelia, a preschool teacher, wants to estimate the mean score on preliteracy tests for the population of three-year-olds. She draws a simple random sample of 20 students from her class of three-year-olds and records their preliteracy scores (in points) 74,79,83,85, 88, 90, 94,95, 95,97,99,99, 100, 103, 105, 105,106, 107, 107, 108 Click to download the data in your preferred format. CrunchIt! CSV Excel JMP Mac Text...
Below is the data for the exam scores of a sample of 9 students. The population is normally distributed. 85, 70, 66, 95, 77, 94, 65, 79, 84 a)Find the margin of error for a 95% confidence interval for the mean. Round to 3 decimal places. b)Find the confidence interval for the mean. Round to 3 decimal places.
Three experiments investigating the relation between need for cognitive closure and persuasion were performed. Part of the study involved administering a "need for closure scale" to a group of students enrolled in an introductory psychology course. The "need for closure scale" has scores ranging from 101 to 201. For the 78 students in the highest quartile of the distribution, the mean score was x = 176.50. Assume a population standard deviation of σ = 8.09. These students were all classified...
A survey of 160 students is selected randomly on a large university campus. is that 96 of the 160 students responded An approximate 95% confidence interval is 0 524 0 676 They are asked if they use a laptop in class to take notes The result of the surve es Complete parts a through d below. a) How would the confidence interval change if the confidence level had been 90% instead of 95%? The new contidence interval would be narrower....
A certain test preparation course is designed to help students improve their scores on the GRE exam. A mock exam is given at the beginning and end of the course to determine the effectiveness of the course. The following measurements are the net change in 55 students' scores on the exam after completing the course: 6,14,12,23,06,14,12,23,0 Using these data, construct a 95%95% confidence interval for the average net change in a student's score after completing the course. Assume the population...