Methods of Communication
Research and Statistics
Online Workbook
SPSS exercise 2.3
For this exercise, we are using the MediaUse.sav database.
a. You would like to know what the 'mean' age of the respondents who have filled in the questionnaire is. Use variable 'v3' for this. What level of measurement does this variable have?
ratio
b. Which measure of central tendency should/could you therefore use? And what is its value?
The mean age is 36.03
c. You now want to know what the 'middle' age is. In other words, the age above which 50% of the respondents are older, and below which 50% are younger. What measure of central tendency should you now take? Name it, and the value.
the median age is 28
Hints
1 How do I recode? Some variables have a lot of values. For example, if you ask a random person how old they are, you would hypothetically get a value between 0 and 117. But if you ask 1,000 people how old they are, you would get a whole range of different values, of which it might prove tricky to get any kind of overview. In such cases, it would be useful to group the values, and to make a new category of that variable. First, list a number of categories on paper, such as:
2 Determining the level of measurement of a variable Nominal scale In a nominal scale, the characteristics are assigned a random value. The sequence of the characteristics does not matter, as can be seen on the scale below. Moreover, the distance between the letters themselves has no real meaning.
3 1 4 5 2
Ordinal scale In an ordinal scale, the characteristics are not assigned a random value, but the scale shows their rankings. This can be seen on the scale below. The values are in alphabetical order. The distance between the letters remains random, however, and without any real meaning.
1 2 3 4 5
Interval scale In an interval level of measurement, the scale indicates a sequence. The distance between the letters themselves also has real meaning. For example, the difference between '2' - '1' = '4' - '3' and the distance '3' - '2' = '5' - '4'. However, there is no zero point. An example of an interval scale is the temperature in degrees Celsius. The difference in temperature between 5 and 10 degrees Celsius is the same as that between 35 and 40 degrees. However, the zero point is random - in other words, 0 degrees Celsius is not the lowest possible temperature. This means that you cannot say that 40 degrees Celsius is four times greater than 10 degrees Celsius, because the relationships between two numbers are not the same (because of the lack of identical distances, and a natural zero point).
1 2 3 4 5
Ratio scale The ratio scale has all the same characteristics of an interval scale. But it also has a natural zero point (0). This means that the differences between the numbers on the scale have a real and identical meaning, as does the relationship between two numbers. Therefore, you can say that a person who has four children has twice as many children as someone who has two.
0 1 2 3 4 5
3 Measures of central tendency and measures of dispersion selection chart
| Measure of central tendency | Mode | Median | Mean | |
| Measure of dispersion | Interquartile range | Standard deviation, Variance | ||
| 1. Select | 1.1 Specifics | What occurs most frequently? | What is the median value? | What is the balance point of the distribution? |
| 1.2 Minimum level of measurement | Nominal | Ordinal | Interval | |
| 1.3 Shape of the distribution | Usable with every distribution shape | Usable with every distribution shape | Not optimal for very skewed distributions | |
| 2. Calculate | Analyze-> Descriptive Statistics -> Frequencies -> Statistics | Analyze-> Descriptive Statistics -> Frequencies -> Statistics | Analyze-> Descriptive Statistics -> Frequencies -> Statistics | |
| 3. Check | Unusable with a distribution with many peaks, e.g. in the case of an ungrouped interval variable. | The greater the difference between the mode, median, and the mean, the more skewed the distribution. | ||
| 4. Conclude | General:
1. Give your reasons for selecting the measure of central tendency and measure of dispersion (see Select and Check). 2. Use the value of the measure of dispersion to comment on the accuracy of the calculated measure of central tendency: the smaller the distribution, the better the centre typifies the distribution. |
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| Mode: "The most common value of variable X is A.". | Median: "The median value of variable X is A" or "Half of the units of analysis have A or less on variable X, and half of the units of analysis have A or more on variable X." Interquartile range: "The mean deviation from variable X compared to the median is A" or "The middle half of the observations lies between (first quartile limit) and (third quartile limit). |
Mean: "The units have an average A on variable X." Standard deviation, Variance "The mean deviation in relation to the mean." |
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4 What is a syntax? A syntax contains the SPSS commands. You do not have to work with syntaxes yet on this course. The only thing you need to know is how to paste a syntax into an answer field, so that we can check whether you have carried out a valid analysis and taken the right steps to arrive at your analysis. When you carry out an analysis in SPSS and confirmed it by clicking on OK or Continue, the results of your analysis will appear in the output screen. In some versions of SPSS (depending on the settings), the syntax appears at the top of the output screen as standard.
Copy the text that appears at the top to the answer field of the exercise for which the syntax is required. In other words, only copy the text - the syntax - to the answer field, and not the tables!
There is another way of generating the syntax. The main advantage of this method is that you can store the syntaxes separately and make notes in them for a subsequent occasion. Normally, you confirm every analysis that you carry out in SPSS by clicking OK (or Continue). Next to or under the OK button, there is also a Paste button. If you click Paste instead of OK, then a separate syntax window will appear automatically containing the syntax of the command you have given.
Note: You have not yet given the command to SPSS to conduct the analysis! You can now copy the syntax and paste it in the answer field in the interactive workbook (select the syntax and press Ctrl+C, and paste by using Ctrl+V).For SPSS to conduct the analysis, you must first click Run.