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Descriptive statistics_Measures of central Tendency and Dispersion


Measures of central tendency are the central or middle or average values. These are mean, median and mode.

Mean (popularly called arithmetic mean) is the sum of all observations divided by number of observations.
Median is the middle value in terms of location when the observations are sorted in ascending or descending order.
Mode is the most repeated observation and usually lies in the center of distribution in case of normally distributed data

Measures of dispersion are the values that show the spread-ness of the data. The most commonly used measures of dispersion are: range and standard deviation.

Range shows how much the observation is spread in terms of extreme values. So, range is the highest value minus lowest value.
Standard deviation shows the dispersion of observation from the mean. It is the root mean squared deviation of individual observations from the mean.

Steps to calculate measures of central tendency and dispersion using SPSS

Let’s work on sample data in SPSS (e.g. demo.sav from your installation directory) or any data of your own. We can do by any one of the following two methods.

Method 1

Step 1. Identify the numerical variable (such as age, height, weight, income etc.) which is entered in number form and whose calculation of measures of central tendency and dispersion is meaningful.
step 2: Click on analyze, descriptive statistics and then frequency

Step 3: Move the desired variable (e.g. income) to the right hand side. The numeric variable will show the scale sign while the categorical variables will show balloon sign. Only move one with the scale sign.

 Step 4: Click on statistics and select (tick mark) the desired measures of central tendency and dispersion.

Step 5: Click on continue
Step 6. Deselect (remove tick mark) the option "display frequency tables" because the table generated will be very big (and not desired this time). But we want the table as well, we may not deselect this option. We normally generate the frequency tables for categorical data which will be discussed later.


 Step 7. Click on ok and you will see the desired output.

Method 2

Step 1: we click on analyze, descriptive and descriptives (not frequency)

Step 2: After that we move the desired variable to the right
Step 3: When we click on option, the most commonly used measures will be shown selected by default (already tick marked while we open)
Step 4. Now, we click additional options if we want to and then click continue and then click ok. After that we get the following output.


After that, we can utilize the output accordingly. 
Good luck and see you all in the next tutorial.

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