Descriptive statistics: the type of statistics used to summarize or
describe data. It deals with the presentation of numerical facts, or data in the
tables or graphs form, and with the methodology of analyzing the data.
There are two main types of descriptive statistics:
1- central tendency: central tendency is a score that indicates where the
center of distribution tends to be located. It tells us about the shape and
nature of the distribution.
Measures of central tendency:-
The mode: the most frequently occurring score or the most frequent measurement.
the mode is :4
the mode is :7
the mode is :122
*If no number is repeated in the data set, there is
the median: If there is a number values in data set, then the median is the
mean of the two middle values.
*the median is a best measure of central
for the data set : 6-9-1-2-6-5-1
arrange from lowest to highestd : 1-1-2-6-6-9
the median is the mean of 2 and 6
Rearrange from lowest to highest
Middle value – 137
The median is : -137
Rearrange from lowest to highest:
Middle values – 16 and 20
Median = (16 + 20)/2 = 18
The Median is = 18
Mean: The summation of all data
values/number of data values
Calculate the mean:
2-types of variability:
Range: the range is simply the difference between the highest and lowest number
in a set of numbers.
to measure the range we need :
variance: variance is the average of the squares of the deviations of the
observed numbers from mean .
– the square will always give positive values
standard deviation: the standard deviation (std dev) is the average deviation
of the values from the mean or the average spread.
– it is always positive
-the std dev is a basic building block for analyzing our data.
Types of variables:
Quantitative data: consist of values representing counts or measurements .
Qualitative data (or non- numeric ): consist of values that can be placed into
non numeric categories .
two levels of qualitative data:
Nominal level (by name)
– no natural ranking or ordering of the data exists.
Ordinal level ( by order )
-provides an order , but can not get a
precise mathematical difference between levels.
Importance of descriptive statistics :
the descriptive statistics is very important because we can use it to make or
measures graphs and charts and its very important to measure central tendency
and useful to summarize the data or values.