1 tutorial 2 ge 5 tutorial 2 rules of engagement no computer or no power → no lesson no computer...
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GE 5 Tutorial 2Tutorial 2
rules of engagementrules of engagement• no computer or no power → no lessonno computer or no power → no lesson• no SPSS → no lessonno SPSS → no lesson• no homework done → no lessonno homework done → no lesson
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Steps in the research process
• collecting data: Exproting from LimeSurvey• processing and displaying data: SPSS
• Today an important part: chapter 3 and 5 (standard deviation) (Howitt and Cramer)
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Content seminar 2
1. Quiz (chapters from Howitt & Cramer)2. Discussion homework (assignment 1 + 2)3. Describing variables numerically (chapter
3 + 5 Howitt & Cramer)4. Importing a websurvey (LimeSurvey)5. SPSS workshop6. Discussion homework next week
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1. Quiz
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Quiz
• Chapter 1, 2 & 3 Howitt & Cramer• Password:
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2. Discussion homework
Questions about! Deadline Friday
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Describing variables numerically: Averages, variation and spread
• Introduction• Typical scores: mean, median and mode• Comparison of mean, median and mode• The spread of scores: range, min, max,
variance, standard deviation.
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Measures of central tendency
• mean or 'arithmetic mean' (page 25-26)• median (page 26-27)• mode (page 27-28)
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1. Mean
• The mean is calculated by summing up all of the scores in a distribution and dividing it by the number of scores.
• In statistical notation:
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Statistical notation
Statistics uses basic mathematicaloperations and notation, but also somespecific notation:• Scores are referred to as X (and Y, etc.).• N is the number of scores in a population
and n is the number of scores in a sample.• The frequently used symbol Σ (Greek
capital S) stands for ‘summation’.• The summation sign (Σ) instructs you to add
up a set of scores. The Σ is followed by a symbol or equation that defines what is to be summed.
• NOW calculate Σ X.• Use the formula to calculate the mean
nr X1 2
2 3
3 1
4 2
5 2
6 1
7 3
8 3
9 3
10 2
11 1
12 1
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3. Mode
• The mode is the most frequently occurring category
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Mode
Most frequent value in a distribution
1 2 3 4 5 6 7 8
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Mode
1 2 3 4 5 6 7 8
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2. Median
• The median is the midpoint of the scores in a distribution when they are listed in order from smallest to largest.
• The median divides the scores into two groups of equal size.
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Median
The value in the middle of the distribution
1 2 3 4 5 6 7 8
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Median
The value in the middle of the distribution
1 2 3 4 5 6 7 8
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Mean
The point of balance in the distribution
1 2 3 4 5 6 7 8
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Mean
The point of balance in the distribution
1 2 3 4 5 6 7 8
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Mean
The point of balance in the distribution
1 2 3 4 5 6 7 8
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Mean versus median
Mean and median measure central tendency,
using two different concepts of “middle”:•Mean is the balance point of a distribution: defined by distances
•Median is the midpoint of a distribution: defined by number of scores
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Calculate the mode, median and the mean of the following scores:
• 3, 3, 3, 3, 3, 3• 0, 0, 0, 0, 0, 0, 0, 0,10, 50• 331, 331, 331, 332, 335
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Central tendency and level of measurement
mode median mean
nominal Yes
ordinal Yes Yes
interval/ratio Yes Yes Yes
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Variability / Dispersion Overview
Variability, spread and dispersion are all terms to describe how similar the values of X are to each other.
The focus will be on four ways to describe variability:•minimum & maximum•range•variance•Standard deviation
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Range
• Minimum & maximum• Range
Calculate the minimum, maximum and range of the following values:
3, 5, 4, 3, 7
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Variability is necessary next to mean
report marks: 10
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9
8
10
8
5
5
4
2
mean 7,0
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Variabilility
report marks: 10 7
9 7
9 7
8 7
10 8
8 7
5 7
5 7
4 7
2 6
mean 7,0 7,0
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Range
report marks: 10 7
9 7
9 7
8 7
10 8
8 7
5 7
5 7
4 7
2 6
range 8 2
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Range is still not precise enough
report marks: 10 10
9 7
9 7
8 7
10 7
8 7
5 7
5 7
4 7
2 2
range 8 8
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Variance
• Symbols used: s2, insert sigma, var• defining formula• computational formula (page 32-33): less
important• frequently used in statistics• variance estimate, used for samples (page
34)
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Standard deviation
• mean deviation from the mean
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4. LimeSurvey
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5. SPSS workshop
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Data BIG smartie survey 2014
• Export from LimeSurvey• Import in SPSS• Check variables• Check cases on outliers and exclude them
from a copied dataset• Check measurement levels• Define missing values
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Step 1: Export data from LimeSurvey
• Start Limesurvey
• Open
• Button Responses and Statistics
• Button (export results to SPSS)
• Download syntax file and data file
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Step 2: Import data in SPSS
• Open the SPSS syntax file downloaded from LimeSurvey (SPSS will start)
• Adapt line x: fill in (after FILE = ) the name of the data file (including extension and complete path to the file!) and put the name between quotation marks
• Choose 'Run/All' (or select all and push the green arrow)
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Variable name and labels
• name: variable name• label: variable labels• values: value labels
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Variable type and measure
Type:• numeric: figures (real figures and codes)• string: names etc. (no mean calculation
etc.)• other: less important (dates etc.)
Measure:• scale• ordinal• nominal
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Defining missing values
Specify missing values to remove missinganswers in your analysis:
• Go to screen ‘Variable View’• Click on the grey square in [MISSING] column
• Provide (one or more) missing values• Close with [OK]
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Measures in class SPSS assignment
Measures of central tendency: on different levels of measurement
• Mean• Median• Mode
Measures of variability:• Range (and minimum and maximum)• Variance• Standard deviation
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Data transformations
• Recoding variables (Recode)• Computing new variables (Compute and
Count)
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6. Homework
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Some terms to remember
• central tendency• mean• median• mode• variability, spread• Range• Minimum
maximum• variance• outlier
• …
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Homework: Assignment 3
• See Moodle