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A consumer advocate was interested in the effectiveness of E…

A consumer advocate was interested in the effectiveness of Evelyn Wood’s Speed-Reading Course.  One hundred students were randomly sampled from a population of college sophomores.  Two groups of fifty students were created using random assignment.  Group A (treatment) received the course while Group B (control) was instructed to use whatever means necessary to improve reading speed and comprehension.  After the course, a reading achievement test was given to the students in each group (higher test scores indicate higher levels of speed and comprehension), and the results were as follows: Group A (Treatment) Group B (Control) n 50 50 Mean 75 80 SD 23 20 Suppose the observed P-value for testing the null hypothesis that the population mean difference is zero was 0.06 (it isn’t).  That means that

Two methods of teaching statistics are to be compared.  Meth…

Two methods of teaching statistics are to be compared.  Method A (traditional) involves lectures, textbook, and study manuals.  Method B (experimental) involves the use of computerized instruction, with each student using the computer whenever s/he pleases for as long as s/he pleases.  From the 32 students who enrolled for this course, one-half were randomly assigned to each method.  At the end of the semester, a valid achievement test was given to the students in both groups.  The results of this study will be used to help decide if Method B should be adopted in place of Method A.  The following summary statistics were obtained: Method A Method B n 16 16 Mean 50 57 SD 10 10 The researcher decided to construct a two-sided 90% confidence interval for the population mean difference.  Assuming the estimated standard error was 3.0 (actually it was not) and using the sample data provided, which of the following represents the appropriate interval?

A company that produces light bulbs advertises that the mean…

A company that produces light bulbs advertises that the mean life expectancy of its bulbs is at least 750 hours.  The Consumers Union suspects that the mean life span of the light bulbs is in fact less than 750 hours.  If it can prove this is the case, it plans to bring charges against the company for false advertising.  An employee of the Consumers Union decides to investigate the mean life of the light bulbs produced by the company.  She selects a random sample of 30 of this company’s light bulbs, subjects them to normal use, and measures for each light bulb the number of hours until it burns out.  The results for the sample of 30 bulbs are:  Mean = 700 hours,  and SD = 160 hours. What is the estimated standard error of the sample mean?

Two formats for a new series of social studies textbooks are…

Two formats for a new series of social studies textbooks are being considered.  The first has questions at the beginning of each section of the book.  The second has the same questions at the end of each section.  A small preliminary study was undertaken by the publisher to examine the preferences of teachers.  Twenty-four teachers were randomly selected from the list of all teachers in the city of Chicago.  The publisher met with these teachers.  Samples of both formats were given to the teachers.  After examining both types of textbook, the teachers identified the format they preferred.  Eighteen of the 24 teachers favored questions at the beginning.  The outcome of interest to the publisher was the proportion of teachers who favored questions at the beginning.  Let p represent the population proportion of teachers who favor questions at the beginning. If  Ho: p = 0.5  and the sample proportion is 0.75, what is the standard error of the sample proportion for testing the null hypothesis?