Your Name __________________________________    
Psychology 201W, Spring 2002  
Dr. John A. Johnson

Lab assignment #5 -- Computing z-scores
Due in lab Friday, February 22)

This lab is worth 20 points.

  1. Retrieve the data file of our in-class memory experiment (see table below) either by opening the file lab5.xls in the PSY201W folder on the I-Drive if you are in one of the campus computer labs or by browsing with Microsoft© Internet Explorer (Netscape will not work) to Column A refers to the Participants in the study. Column B indicates the group to which each participant was assigned: Group 1 received the picture without the relationships in the story, and Group 2 received the picture containing the relationships in the story. Column C contains the ratings of comprehensibility ratings; we'll call this variable x. Column I lists the number of sentences remembered; we'll call this variable y.
  2. Using the =SUM spreadsheet function, compute the sum for comprehensibility in cells C45 and cell and the sum for sentences remembered in cell I45. Using either =C45/43 and =I45/43 or the =AVERAGE spreadsheet function, compute the mean for comprehensibility in cell C46 and the mean for sentences remembered in cell I46. Using these means, compute deviation scores for comprehensibility in column E and deviation scores for sentences remembered in column K. Compute squared deviation scores for these two variables in columns F and L, respectively. For example, in cell F2 you would type =E2^2. Using the original formulas taught at the beginning of the course, compute the sum of squared deviations (SS) in cells F45 and L45, the variance (S2) in cells F46 and L46, and standard deviation (SD) in cells F47 and L47 for the two variables. Next, verify that the values you obtained for the variance of the two variables can be obtained by the computational formula on page 130 of the textbook. Do this by first squaring the original scores; these values go in column D for comprehensibility and columns J for sentences remembered. Sum these squared scores with the =SUM spreadsheet function and put the results in cells D47 and J47. Write the computational formula for variance from page 130 in the space below. Then plug in the values for the sum of the x's (Capital Greek Sigma Symbolx) from cell C45 and the sum of the x2's (Capital Greek Sigma Symbolx2) from cell D47 (for comprehensibility) and the sum of the y's (Capital Greek Sigma Symboly) from cell I45 and the sum of the y2's (Capital Greek Sigma Symboly2) from cell J47 (for sentences remembered), n (the number of observations), and compute the result.



  4. Using the appropriate formula, compute z-scores for comprehensibility in column G and for sentences remembered in column M.
  5. The sum of any set of z-scores should be _______. Verify that this is true for the z-scores in columns G and M by computing the sums in cells G48 and M48.The standard deviation for any set of z-scores should be ______. Verify that this is true for the two sets of z-scores by computing the SD with the =STDEV spreadsheet function and entering the results in G49 and M49.
  6. Using "save as" from the Excel file menu, save your Excel file to the floppy disk you use for email. Name the file with the three letters and numbers in your access id followed by lab5.xls. For example, a person whose access id is gmr102 would save the file as gmr102lab5.xls. Email your spreadsheet as an attachment file to Dr. Johnson at by next Friday, February 22nd. This completed lab assignment sheet. should also be turned in on that day.