A researcher administered to 20 college students a test of attention that is used to diagnose ADHD. The test has been administered to so many healthy people that we can comfortably say that the population mean score is known to be 100 and the population standard deviation is known to be 10. Use the data set assigned to you by your Lab Instructor to do as instructed below.

Paste your data set into the first column of an Excel Spreadsheet.

Show each distribution of scores listed below. On the x axis show the range 60 – 180 using bin widths of 10.

the frequency distribution. (5)

the probability distribution. (5)

Measures of central tendency.

Show the equation used to compute the mean (y). (5)

Define “median” and “mode” in words. (5)

Compute the sample mean, median, and mode by hand. (5)

Use Excel to compute the sample mean, median, and mode.

Use the Excel functions =average(DataRange), =median(DataRange), and =mode(DataRange). (5)

Why can’t Excel compute the mode? (5)

Measures of dispersion.

Define variance in words. (5)

Population variance and sample variance: (5)

Give the equations for each.

Which is computed exactly as described in the definition?

Compute sample variance by hand. Learn this method thoroughly—you will use it for most labs.

In the second column of your spreadsheet, to the right of the first data point, use the Excel function shown above to compute the mean of all scores.

Add “$” to the function (F4 key for Windows computers) so that you can copy and paste the function without changing the cells to which the function refers.

Copy the function and paste it below in the cells to the right of each data point.

In the third column compute the deviations from the mean y-y.

In the fourth column square the deviations from the mean using the Excel formula =cell^2.

Sum all of the squared values using the Excel function =sum(CellRange).

Give the name of the value you just computed and the name of its divisor.

Compute variance.

Compute the sample standard deviation of the scores. (10)

Show a snipped screen image of the variance computation in the Excel worksheet. (5)

Sampling error of means.

Define sampling distribution and sampling error. (5)

Use the sample variance computed above to estimate the population variance of the mean and the population standard error of the mean. (5)

Use the population variance of test scores to compute the actual population variance and population standard error of the mean. (5)

Construct the following confidence intervals twice—once using the σ shown above and again using the estimate s.

Construct a 95% confidence interval around each score in the data set using y±Zα/2σy and y±tdf,αsy. (7.5)

Construct 95% confidence intervals around the sample mean using y±Zα/2σy2N and y±tdf,αsy2N . (7.5)

Print your Excel spreadsheet showing values. (5)

Print your Excel spreadsheet showing formulae, adjusting your column widths so that your formulae can be seen by the grader. To do this, click the “Show Formulas” option in the “Formulas” menu. (5)