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Mathematics: SPSS Descriptive Statistics

Mathematics support for students at the University of Suffolk.

Descriptive Statistics in SPSS

You will need to download and open the SPSS file titanic.sav

The file contains data for the SS Titanic which sailed, and later sank, in 1912. The data shows passenger class, passenger age, passenger gender and whether the passenger was a surviver.

Variable View:

Data View:

The data can be summarised via the 'Descriptive Statistics' part of the 'Analyse' menu. Let's explore Analyse -> Descriptive Statistics -> Frequencies. 

This will open up a new dialogue box:

We can use this to make frequency tables of the variables. Statistics can be calculated and graphs can be drawn. Let's make frequency tables for the categorical data: Passenger Class, Passenger Gender and Passenger Survived.

Ensure that 'Display frequency tables' is checked. Click on one of the three categories required in the left most box and then press the arrow button in the middle to move to the right hand box. Do the same for the other 2 categories.

Click on the 'Charts' button and choose the option to draw a bar chart (or a pie chart if you prefer). Press 'Continue' the 'OK'. Output will now be written to the output window.

The frequency tables summarising the data are:

You should also find the charts that were selected.

The descriptive statistics feature of SPSS can also give summary statistics such as the mean, median and standard deviation. We have some scale data in the form of the passenger's age. Go back to Analyse -> Descriptive Stats -> Frequencies and return the previously moved categories back to the left box. Move over the 'Passenger's Age' variable to the right box.

Choose the measures that you would like to get by clicking the check boxes.

Click continue. The frequency table is not needed for these data so uncheck and uncheck the options inside the chart menu.

When ready click 'OK'

Above the chosen options were Mean, Median, Mode, Std. Deviation, Minimum and Maximum. 

 

Continuous variables can also be analysed using the 'Descriptives' menu in SPSS. Go to Analyse -> Descriptive Statistics -> Descriptives.

First move the variable 'Passenger Age' to the 'Variable(s)' section.

Click on the 'Options' button. We can choose the statistics we want computed. Select those shown in the picture below:

The mean is a measure of average (sum of the values divided by the number of values). Standard deviation measures the spread of the data and can be used to describe normal distributions. Skewness is a measure of how symmetrical the distribution is. Values of skewness close to 0 represent symmetry, positive values mean that there are some high valued outliers and a negative value means some low valued outliers.

(image from www.managedfuturesinvesting.com)

Kurtosis values refer to how peaked the distribution is. A normal distribution would have a value of 0. Negative values mean that the distribution is flat, i,e, many cases in the extremes) and positive values meaning the distribution is clustered in the centre. 

Choose 'Continue' and 'OK'

The descriptives provide the requested information about the passenger age on the titanic.

 

Below is a 6 minute youtube video covering descriptive statistics in SPSS.