POL 242 Introduction to Research Methods Assignment One Tutorial Descriptive Statistics June 2, 2011...
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Transcript of POL 242 Introduction to Research Methods Assignment One Tutorial Descriptive Statistics June 2, 2011...
POL 242Introduction to Research Methods
Assignment One TutorialDescriptive Statistics
June 2, 2011
Anthony Sealey [email protected]
http://individual.utoronto.ca/sealey
Agenda
(1) Introduction • (2) Review
(i) Types of Variables (ii) Principal Descriptives
(iii) Webstats(3) Descriptives in Webstats(4) Exercise in Webstats
Introduction
Please be sure to sign the attendance form.
Research QuestionsReview of Types of Variables
Research QuestionsReview of Principal Descriptives
Research Questions1. Measures of Central Tendency
Research Questions“Pick a number …”
Research Questions“… close counts.”
Research Questions1, 2, 3, 4, 5, 6, 7, 8, 9, 10
n
where ‘n’ denotes the number of elements
S xi _______
n
Mean (x) =
(1+2+3+4+5+6+7+8+9+10)
10
Mean =
Mean = 5.5
i = 1
_
Research Questions1, 2, 3, 4, 5, 6, 7, 8, 9, 100
Research Questions
Median: After arranging the data from highest to
lowest, the median is the
value in the middle.
Research Questions“… close doesn’t count.”
Research Questions1, 2, 2, 3, 4, 5, 6, 7, 8, 9
Research Questions
Mode: The value that occurs with the highest
frequency (i.e. the value that appears most
often).
Research Questions2. Measures of Dispersion
Research Questions1, 2, 3, 4, 5
n where ‘x’ denotes the Mean
S (xi – x)2 _________________
n – 1 (1-3)2+(2-3)2+(3-3)2+(4-3)2+(5-3)2
5 – 1
Mean =
Mean = 2.5
i = 1Variance (s2) =_
_
where ‘s2’ denotes the Variance
Variance(s) =StandardDeviation
√ (s2)
√ 2.5Variance (s) =
1.58114Variance (s) ≈
Research QuestionsDescriptive Statistics
Measures of Central Tendency Measures of Dispersion
Mean Median Mode Variance Standard
(m) (s2) Deviation (s)
Nominal ü
Data TypeOrdinal ü ü
Interval ü ü ü ü ü
Ratio ü ü ü ü ü
When to use key descriptive statistics:
Research QuestionsReview of Webstats
• There are four basic steps to the • analysis of a variable in Webstats: • (1) Select a dataset. • (2) Run a ‘frequency’ to understand
how the variable is coded. • (3) Refine the variable. • (4) Perform the analysis.
• In today’s tutorial we’ll use the 2006 • CES to consider three variables: • (1) A citizen’s province. • (2) Citizen’s preferences for or
against income redistribution. • (3) Citizen’s evaluations of the
competence of political leaders.
Research Questions
I strongly recommend going to my site, downloading the ‘code’ file and following along:
http://individual.utoronto.ca/sealey
Research Questions
Step One: Select the dataset
• Go to the course website located at: http://groups.chass.utoronto.ca/pol242/ • Go to: Webstats > Start Webstats.• In section 1, select ‘CES 2006’.• In section 3, select ‘Syntax Method’.• Hit <PROCEED>.
Research Questions
Step Two: Run a Frequency
• Let’s begin with the ‘province’ variable. • To run a frequency, use this code:
fre VAR = province.• Given that this variable has no missing
values and does not require a recode, we can skip the third step (‘refine the variable’) and go to the fourth (‘perform the analysis’).
Research QuestionsMoving on to the next variable …
Research Questions
The question wording for ‘cps_f6’ in the 2006 iteration of the Canadian Elections Study:
Research Questions
Step Two: Run a Frequency
• Since we’ve already selected the dataset, we don’t need to repeat step one. • To run a frequency, use this code:
fre VAR = cps_f6.
Research Questions
Step Three: Refine the Variable
• Notice the ‘don’t know’ and ‘refused’ responses. These responses take on the values of ‘8’ and ‘9’ respectively. We’ll want to code them as missing, and then rerun the frequency: missing values cps_f6 (8,9). fre VAR = cps_f6.
Research QuestionsAnd finally …
Research Questions
The ‘cps_h2b0’ and ‘cps_h2d0’ variables in the 2006 iteration of the Canadian Elections Study asks about respondent’s perceptions of levels of political leaders’ competence. In today’s tutorial, we’ll focus on the two most successful political leaders in the 2011 election.
Smiling Jack
Smiling Stephen
Research Questions
Step Two: Run a Frequency
• Since we’ve already selected the dataset, we don’t need to repeat step one. • To run frequencies, use this code:
fre VAR = cps_h2b0. fre VAR = cps_h2d0.
Research Questions
Step Three: Refine the Variables
• Notice the ‘don’t knows’ are coded as ‘98’. To code them as missing, use this code: missing values cps_h2b0 (98). fre VAR = cps_h2b0.
missing values cps_h2d0 (98). fre VAR = cps_h2d0.
Research QuestionsDescriptives in Webstats
Research Questions
Once we’ve refined our variables, the final step is to perform the analysis. To obtain descriptive statistics, we do this by simply adding some extra code at the end of our frequency command.
Research Questions
Step Four: Perform the Analysis
• Suppose we want to find the mode of the ‘province’ variable; in order to do this, we simply add ‘/statistics=mode’ at the end of our frequency command: fre VAR = province/statistics=mode.
Research Questions
• If we want other descriptive statistics, simply include the appropriate code at the end of the frequency command.• For example, if we want to know the
median, mean, variance and standard devation, simply add ‘/statistics=median mean variance stddev’ at the end of our frequency command.
Research Questions
Use appropriate descriptives for each level of measurement. • For nominal variables, find the mode: fre VAR = province/statistics=mode.
• For ordinal variables, find the mode and median: missing values cps_f6 (8,9). fre VAR = cps_f6/statistics=mode median.
Research Questions
• For interval/ratio variables, find the mode, median, mean, variance and standard deviation: missing values cps_h2b0 (98). fre VAR = cps_h2b0/statistics = mode median mean variance stddev.
Research Questions
We can use the means and standard deviations of similar variables to compare them. • For example, if we want to compare
perceptions of Jack’s and Stephen’s competence, use this code: missing values cps_h2b0 (98). fre VAR = cps_h2b0/statistics = mean stddev.
missing values cps_h2d0 (98). fre VAR = cps_h2d0/statistics = mean stddev.
Research Questions
Once we’ve completed our analysis, we’ll be prepared to ‘tell the story’. In other words, what have we learned from our analysis? When doing this, use the information we’ve gathered from the frequency distribution as well as from the appropriate descriptive statistics.
Research QuestionsExercise in Webstats
Research Questions
Exercise
Choose a public opinion dataset that you are interested in. Find a variable for each of the nominal, ordinal and (interval or ratio) levels of measurement. Run frequency distributions, refine the variables by declaring missing values and performing necessary recodes and calculate appropriate descriptive statistics for each of the identified variables. What’s the ‘story’ of your analysis? What have you learned?