Psychology statistics

Before attempting this assignment you should have carefully read and studied Ch01 in the textbook. In addition to the textbook sections I emphasized for the first assignment, be sure you understand the distinctive features of the three data structures discussed on pages 19-27 and the differences between them. Also study the Ch01 discussion posts titled What is an observational unit?, Better terms for independent and dependent variables, and Variables and scales of measurement. You should have also carefully studied Tidy Data, watched the relevant videos in the Ch01 folder, and watched the Jamovi videos.

Download the Ch01 Homework.docx file that’s attached to this assignment and save it on your computer where it will be easy to find. You’ll answer the questions on it and attach it when you submit this assignment.

For this assignment you’ll use two tools for working with data:

• Jamovi
• A spreadsheet program such as Excel, Google Sheets, or LibreOffice

Carefully review the concept of tidy data in Tidy Data. You’ll then organize the data in Step 1 of Figure 1.3 (p. 9 in the print edition of the textbook) in tidy data format by following the steps in the enumerated list of instructions below. Remember that in the tidy data format, there’s a column for each variable and a row for each observational unit with the first row containing the names of the variables. In Figure 1.3 the observational units are the 12 students for whom we have scores. We’re given information about two variables, but we’re not given the names of these variables, so you’ll have to assign names to them yourself. They should be short and descriptive, like the variable names in Tidy Data. One variable is the format in which the text was presented to the students. Half of them got it in print and half got it on a screen. You should understand that this is a variable because the values vary or differ between students; some students got text in one format and others got it in the other format. In addition to coming up with a name for this variable, you also have to come up with names for the two levels of the variable. Those two levels are text presented in print and text presented on a screen, as explained above. As with variable names, level names should also be short and descriptive.

The other variable is the score the students got on the test they took to assess their understanding of what they read. Hopefully it’s clear why this is a variable. Think up a short, descriptive name for this variable.

This data set could have included another variable – one that identifies the observational units, that is, the individual students. In some data sets it’s important to be able to identify each observation. For instance, if we needed to know which test score was obtained by each student, this data set would have to include a third variable – a unique identifier for each student. The values of that variable could have been the students’ names or it could have simply been a different letter or number for each student. If a data set includes an ID variable, it’s usually located in the first column.

For this assignment you should create that third variable. You can make up 12 names or you can simply use letters or numbers, one for each observational unit/student, and make up a name for the variable. The 12 names, letters, or whatever, are the values of this variable.

To organize this data set in the tidy data format, use a spreadsheet program, preferably Excel.

1. In the first row of a spreadsheet, enter the names you’ve assigned to the three variables.
2. Then starting in the second cell of the first column, enter the 12 values that identify each student. The last entry in this column should be in row 13.
3. Starting in the second cell of the second column, enter each student’s value on the variable that indicates the format of the text they read. So half the cells in this column should contain the name of one of the two values of this variable and half should contain the name of the other value.
4. Starting in the second cell of the third column, enter each student’s score. Be sure that the scores from Sample A in Figure 1.3 are assigned to the students who read the print text and the scores from Sample B are assigned to the students who read the screen text. This will insure that our results match the results in Step 2 of Figure 1.3.
5. Now that the data set is in tidy data format, use the Save As function to save the file as a .csv (comma separated values) file. Name the file Fig1-3. When you click Save As, you’ll see many format options to choose from. Look through them carefully because you may see more than one type of .csv option. Always choose the plain vanilla option – Comma Separated Values (.csv).
6. Save the file with the name Fig1-3_YourLastName.csv on your computer where it will be easy to find.

Now open Jamovi, locate Fig1-3_YourLastName.csv where you saved it on your computer, and open it. If you’ve done everything correctly your data will appear, looking pretty much the same way it looked in the spreadsheet program.

1. Open the Setup window and make sure the Measure type and Data type are correct for each variable.
2. Click the Analyses tab, then open the Exploration menu and select Descriptives.
3. Move the third variable (test scores) from the box into the Variables box.
4. Move the second variable (reading format) onto the Split by box.
5. In the Results panel you should see Jamovi’s default set of descriptive statistics for each group. If you did everything correctly, the means of the two groups will match the means reported in the textbook.
6. Now open the Statistics menu in the panel on the left. You’ll see that the results in the right panel are the default statistics that are pre-selected from this menu.
7. Now open the Plots menu. Select Histogram and Density. In the Results panel you should see two histograms and density curves showing the distribution of the test scores for each of the groups.
8. Before leaving this example, let’s see if we can answer the question these researchers were asking. This will be a preview of upcoming topics. Open the T-Tests menu at the top and select Independent Samples T-Test.
9. Move the third variable (test scores) into the Dependent Variables box.
10. Move the second variable (print or text) into the Grouping Variable box.
11. From the Additional Statistics menu select Effect Size. The textbook authors say that these data can tell one of two different stories. Either there is no real difference between the printed page and a computer screen or there really is a difference between the two studying methods. Without using the technical terminology that you’ll learn later, the results of Jamovi’s independent samples t-test indicate that there really is a difference. That’s what the p value tells us. Furthermore, the value of Effect size/Cohen’s d indicates that reading from print vs. reading on a screen made a big difference.
12. You can scroll up and down in the results panel. Be sure that panel shows (from top to bottom) the descriptive statistics table, the two distribution plots, and the results of the independent samples t-test. Then open the hamburger menu (top left corner), select Save, and save this file as an .omv file with the name Fig1-3_YourLastName.omv) on your computer where it will be easy to find.

Instructions for submitting this assignment.

1. Locate the Fig1-3_YourLastName.csv, the Fig1-3_YourLastName.omv file, and the completed Ch01 Homework.docx where you saved them on your computer.
2. Click the title of this assignment (Ch01 Homework) to open the Upload Assignment page.
3. In the ASSIGNMENT SUBMISSION section, attach the Fig1-3_YourLastName.csv file, the Fig1-3_YourLastName.omv file, and the completed Ch01 Homework.docx file and click Submit.
4. If you submit this assignment early enough, I might have time to provide feedback that you can use to improve it and possibly improve your grade. So soon after you submit it, return to this assignment to see if I’ve given you any feedback. Click the assignment title and on the Review Submission History page you’ll see the details of your prior submissions. To revise a prior submission, click Start New, download and revise, be sure to save it, and upload it as previously.