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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

9

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