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Poli_399_Tutorial_Week_Three_-_Sept_29th_(2)

1. 1. POLI 399 – Research Methods Week Two Recoding and Creating Variables, Creating Indices and Reliability Scores with SPSS
2. 2. Today’s Agenda <ul><li>Questions on assignment </li></ul><ul><li>Recoding variables </li></ul><ul><li>Creating variables (“IF”) </li></ul><ul><li>Creating an index </li></ul><ul><li>Reliability Scores </li></ul>
3. 3. Recoding Variables in SPSS <ul><li>Why recode variables? </li></ul><ul><ul><li>There are too few cases in one or more categories of a variable to allow for analysis . </li></ul></ul><ul><ul><li>We need fewer categories in the variable. </li></ul></ul><ul><ul><li>We need to build an index to measure a concept more completely, and we need each variable to have the same categories. </li></ul></ul><ul><ul><li>We need to move from an interval variable to a nominal or ordinal level variable. </li></ul></ul>
4. 4. Examples of Recoding <ul><li>Age </li></ul><ul><ul><li>Turn the interval variable “age” or “year of birth” into categories. </li></ul></ul><ul><li>Support for Prime Minister </li></ul><ul><ul><li>Turn four categories (support, somewhat support, somewhat oppose, oppose) </li></ul></ul><ul><ul><li>Into two categories (support and oppose) </li></ul></ul><ul><li>Province of Residence and Region </li></ul><ul><ul><li>Turn province of residence (10 provinces, 3 territories) </li></ul></ul><ul><ul><li>Into five regions (Atlantic, Quebec, Ontario, West and North) </li></ul></ul>
5. 5. How to Recode? <ul><li>Transform menu -> Recode -> Into different variables </li></ul><ul><li>Pick the variable you want to recode -> enter name and label for new variable -> click “Change” -> click “Old and New Values” </li></ul><ul><li>Enter the value or range of values for the value of the new category (For example, for region, NS, NB, NL and PEI are valued 10-13, then enter it into the range pane) </li></ul><ul><li>Enter the new value for the new combined category. </li></ul><ul><li>Do this for all the values in the old variable. </li></ul><ul><li>Click continue and then OK in the next menu. </li></ul><ul><li>Go to the “Variable View” – the new variable will be at the bottom of the list. </li></ul><ul><li>Label the values for the new variable accordingly. </li></ul>
6. 6. In Class Examples <ul><li>Province </li></ul><ul><ul><li>From 12 categories to 5 regional categories </li></ul></ul><ul><ul><li>Atlantic = NF (10) + PEI (11) + NS (12) + NB (13) </li></ul></ul><ul><ul><li>Quebec = Quebec (24) </li></ul></ul><ul><ul><li>Ontario = Ontario (35) </li></ul></ul><ul><ul><li>Prairies = MB (46) + SK (47) + AB(48) </li></ul></ul><ul><ul><li>BC/North = BC(59) + YK (60) + NWT(61) </li></ul></ul>
7. 7. Regional Recode - Output Before recode After recode
8. 8. In Class Examples <ul><li>How do you feel about Paul Martin? (pes_f2) </li></ul><ul><ul><li>Measured on a thermometer scale of 0 (really dislike) to 100 (really like) </li></ul></ul><ul><ul><li>I want to turn this into five categories </li></ul></ul><ul><ul><li>Dislike a lot = 0 to 20 </li></ul></ul><ul><ul><li>Dislike somewhat = 21 to 40 </li></ul></ul><ul><ul><li>Neutral = 41 to 60 </li></ul></ul><ul><ul><li>Like somewhat = 61 to 80 </li></ul></ul><ul><ul><li>Like a lot = 81 to 100 </li></ul></ul>
9. 9. Like Paul Martin Recode - Output Before recode After recode
10. 10. Recoding Recap <ul><li>When we recode a variable, we change the variable’s original code to something we want it to be. </li></ul><ul><li>We must have a theoretical justification for operationalizing variables (recoding). </li></ul><ul><li>We will be recoding variables for the rest of the semester, so it should become easy (or at least easier) with time and practice. </li></ul>
11. 11. Recoding Using “if” Statement <ul><li>New variables can be created using “IF” </li></ul><ul><li>If the result of a conditional expression is true, the case is included in the selected subset. </li></ul><ul><li>If the result of a conditional expression is false or missing, the case is not included in the selected subset. </li></ul>
12. 12. How to create a variable using “IF” <ul><ul><li>Follow the same steps as you would for recoding a variable into a new variable. Use “if” statement when you want specific conditions to be met: </li></ul></ul><ul><li>In SPSS dataset, click on Transform, Recode Into Different Variables </li></ul><ul><li>In the recode dialog box, click IF. </li></ul><ul><li>Select Include if case satisfies condition. </li></ul><ul><li>Enter the conditional expression (=, <, > etc) </li></ul><ul><li>Click on continue, ok. </li></ul>
13. 13. Creating an Index <ul><li>What is an index? </li></ul><ul><ul><li>It is a new variable created by adding together a number of other variables with similar attributes. </li></ul></ul><ul><li>Why create an index? </li></ul><ul><ul><li>To turn a number of similar variables into one variable. </li></ul></ul><ul><ul><li>Simplifies analysis. </li></ul></ul><ul><ul><li>To create a single indicator to fully capture a complex concept . </li></ul></ul><ul><li>Things to think about before creating an index </li></ul><ul><ul><li>Do the variables to be used go together? </li></ul></ul><ul><ul><li>Is there a theoretical basis for putting them together? </li></ul></ul><ul><ul><li>Do they measure the same thing? </li></ul></ul><ul><ul><li>Are the variables measured in the same direction? </li></ul></ul>
14. 14. Creating an Index cont… <ul><li>Examples of indices </li></ul><ul><ul><li>Attitudes towards government. </li></ul></ul><ul><ul><li>Political participation. </li></ul></ul><ul><ul><li>Attitudes towards different policies. </li></ul></ul>
15. 15. In Class Example <ul><li>You are writing your research report on the activities of political parties during an election campaign. </li></ul><ul><li>In the CES 2004 survey, there are three questions that ask if you have been contacted by a political party during the campaign </li></ul><ul><ul><li>pes_co_a (contacted by phone) </li></ul></ul><ul><ul><li>pes_co_b (contacted in person) </li></ul></ul><ul><ul><li>pes_co_c (contacted by mail) </li></ul></ul><ul><li>You want to create an index of political communication to measure the frequency by which voters were contacted by political parties. </li></ul>
16. 16. In Class Example <ul><li>Index Creation Check List </li></ul><ul><li>Is there theoretically justification for creating your index? </li></ul><ul><li>Are all the variables you want to include the index measured in the same way and in the same direction? </li></ul><ul><li>Have you removed the “don’t know”, “r volunteers: have not been contacted at all” and “refused” respondents from the variable? (missing values) </li></ul><ul><li>Have you run a reliability analysis to test whether the variables go together? </li></ul>
17. 17. How to Create an Index <ul><li>Choose the variables to combine </li></ul><ul><li>Make sure the variables are measured in the same direction and have similar values assigned to the different categories. </li></ul><ul><li>If they do not, recode the variables to make them all consistent. </li></ul><ul><li>Make note of the different values assigned to the variables once recoded. </li></ul><ul><li>If needed, remove those who answer don’t know or those who refused to answer the questions (use missing values). </li></ul>
18. 18. Creation of the Index <ul><ul><li>Recode: </li></ul></ul><ul><ul><li>pes_co_a (contact by phone) </li></ul></ul><ul><ul><li>pes_co_b (contact by person) </li></ul></ul><ul><ul><li>pes_co_c (contact by mail) </li></ul></ul><ul><ul><li>1 = contacted by party </li></ul></ul><ul><ul><li>0 = not contacted by party </li></ul></ul><ul><ul><li>Recode ‘don’t know’ or ‘refused’ responses ‘missing’ </li></ul></ul>
19. 19. Creation of the Index <ul><li>Compute a new variable. </li></ul><ul><ul><li>SPSS: transform menu -> compute -> enter the name of the new variable in the “target variable” box </li></ul></ul><ul><ul><li>-> find newly created variables to add to index in list </li></ul></ul><ul><ul><li>-> move them over to the box on the right (“numeric expression”) </li></ul></ul><ul><ul><li>-> add three new variables together </li></ul></ul><ul><ul><li>-> press OK. (Run frequency table to confirm the index ranges from 0 to 3.) </li></ul></ul>
20. 20. Reliability Scores <ul><li>The reliability analysis evaluates what items are to go into the index. </li></ul><ul><li>This function uses the internal consistency approach to reliability. (Cronbach’s Alpha) </li></ul><ul><ul><ul><ul><ul><li>Calculates the number of items going into the index </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Calculates the average inter-item correlation among the variables. </li></ul></ul></ul></ul></ul>
21. 21. Cronbach’s Alpha <ul><ul><ul><ul><ul><li>Ranges from 0 to 1(1 indicates perfect internal consistency and 0 indicates no internal consistency) </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Alpha increases with the number of variables in the index and as the relationships between the component variables become stronger </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Although there are no hard and fast rules, in this class we will consider .40 an acceptable level. </li></ul></ul></ul></ul></ul>
22. 22. How to run reliability scores <ul><li>In SPSS, click on Analyze, Scale, Reliability </li></ul><ul><li>Select two or more variables as potential components of an additive scale (the index). (In our example, pes_co_a, pes_co_b, pes_co_c) </li></ul><ul><ul><li>Ensure in the model pane that ALPHA is selected. </li></ul></ul><ul><li>Click on ok. </li></ul>
23. 23. For next time… <ul><li>We will develop and diagram causal models </li></ul><ul><li>Read Chapter 12, Section B in Jackson and Verberg </li></ul>