In this video we will learn about frequency distributions and once we know about frequency distribution
we will learn how to draw a histogram
to when we are trying to draw frequency distribution.
We are basically trying to summarize the data so that we have different categories from that data and
we assign the number of occurrences of each category in that data.
For example if I have data of students of for college and against their name I have the branch that
they belong to.
I can create a table like this in which I have summarized that how many of those students belong to
each branch.
So in an engineering college in that list hundred students belong to computer science branch 82 and
belong to mechanical engineering branch and so on.
When we have the categories like this that is the categories are discrete we have five different branches
and to each branch we can clearly assign these student.
This is called qualitative data or categorical data.
And this type of distribution is called up frequency distribution for qualitative reader.
So that raw data would be stored in name in front of that is read in the branch to which that's true
and belongs and we have this list for 420 students and we summarize that data as how many students belong
to each group.
Once we have a say in these frequencies we can also find out the relative frequency of each category
by using this formula that is frequency of that category divided by some of all frequencies.
That is if I want to find out the relative frequency of students blank belonging to biotechnology it
is 60 that is the frequency of this category divided by the total frequency which is 420 is equal to
nearly fourteen point two percent.
So when we build a frequency distribution for qualitative data that is there are clear discrete categories
and we draw a graph of it.
It is similar to a bar chart a graphical representation of frequency distribution for qualitative data
is known as budget budget.
We have already discussed we know how to draw a budget.
If we have a data like this you can just select data die in Excel and go to budget and draw this kind
of graph.
The next table frequency distribution is frequency distribution for quantitative data that is continuous
data.
So for example if I have name of student and in front of them I have the marks of these students in
science.
So MOX is a continuous value from zero to hundred.
If I want to straightaway create categories maybe I'll get a hundred categories one category of zero
one category of two.
One category of value 3 and that does not really make a sense.
So when we have a continuous data we try to create ranges small ranges and within each range we assign
the frequency of number of instances belonging to that category.
So for example instead of creating 0 1 2 3 as categories we have greater detail 235 as one category
35 to 55 as a matter to divide 278 added.
And so on and within each range I have found out how many student belong to that range and assign that
number hit to this table is frequency distribution for that continues data.
And when we create a graph of this data that is called a histogram.
So a graph of frequency distribution of categorical variable is called bar chart a graph of frequency
distribution of continuous data is called a histogram.
So how to draw a histogram when you have continuous data.
I have outlined that process in these six steps.
When you have a list of continuous data the first thing you need to decide is the number of classes
that you want.
That is the number of categories.
For example in the previous example we have five classes to first thing you need to decide is how many
classes you want in your table.
Second using that number of classes we find out the class quit using this formula.
The maximum value of data and the minimum value data what is the difference between these two values
divided by the number of classes that we decided in first.
Once we have class weight we can start creating the classes.
We start by the minimum value we add classwork and we get the first class.
This will get clear when we go through the example.
This is the continuous data that I have.
It is a set of 24 numbers and I want to segregate into five equal classes.
So I have selected the number of classes with just five.
Now I want to find out the class which I do classwork this phone by subtracting minimum value from the
maximum value.
Minimum value for this set of numbers is six and the maximum value is 36 to 36 minus six divided by
number of classes which is five.
So it comes out to six now to create the classes.
I will start with the minimum value which is six and I will add the class word to get this upper range.
So it is six to twelve.
Next class will start from this value will and we will add the class word to get it.
And so on.
So from six to twelve will do 18 18 to 24 25 30 32 36 to avoid confusion that if we have a number 30
to which class it will belong we usually follow this convention that party will not belong to this class.
It would belong to this 24 to 30 class that is today will be part of the upper range and not of the
lower range.
Once we have created these classes we have to start assigning each number to these classes.
So I will go to the numbers one by one and I will start adding a mark to each of these classes to whichever
class that number belongs to.
For example I start with 10 and belongs to this class so I add a market.
Then there is 14 14 belong to this class.
I add a mark here.
I go through all these numbers and I continue adding marks in the end.
I have this column containing Ali which is giving me how many numbers belong to each category.
Lastly I just need to add these marks to any frequency.
So this is how this table is created.
And once this table is created we can create a histogram.
So let us go to excel now and create this is to them.
So here is the list of numbers that I had in my presentation and this is the histogram which is created
for these numbers.
The good thing about Excel is that you do not need to create that table to create this histogram Excel
can create this histogram straight away.
Using these numbers you can see from six to twelve we have two from two to 18.
We have four.
So basically these classes are on the horizontal axis and the height of the bar is giving you the frequency
in each class.
One small but important thing to note here is that Excel is using this gold and square brackets to indicate
that which number is included and which is not for example in this 24 to 30 24 number will not be included
in this graph.
Therefore it has a gold bracket but 30 will be included in this bar.
Therefore it is a square bracket so you can see for these four categories the first number is not included
but the second is included.
But for this first category only the first and chicken both are included.
This is our histogram we look like.
Let us learn how to create this histogram and delete this first so to create Instagram select the numbers
that we have go to insert in these statistical graphs.
This first option isn't Instagram you can see by default it has created 3D glasses with the range six
to sixteen 16 to 26 and 26 to 36.
Now I wanted five glasses so for that I will do the format access to open for my taxes.
You know how to open this formatting options either right click and select the format option or you
double click on that chart element to open formatting options for that particular element.
So I double clicked on the horizontal axis to open it formatting options in these.
The third option will have the specific exit options for histogram.
Here you can change the bean rate and number of bins by default automatically created to ribbons.
Now I want to create five bins now either I give a bin rate of value 6 which I found out.
So this is the Instagram that I wanted to see on.
I could have given the number of bent as for you two both will look.
Also remember whenever you draw a histogram it is advisable that you have data labels on top of it.
It will make it easier to find out what is the frequency of each category.
The second type of statistical chart is up but he does chart so this is it.
But he does chart
it is similar to the histogram.
The major differences the categories are sharp weight.
These are sharper in the sense that the category which is contributing the most comes first.
So this category had a frequency of 9 to it this coming first next county category which just contributing
the next maximum to the total.
So the categories are arranged in the descending order of that frequency values.
And this line is showing the cumulative relative frequency values.
For example the relative frequency of this category is around 35 percent.
Then I add this second category it becomes nearly 70 percent of the third category.
It becomes nearly 88 percent after adding fourth category.
It becomes nearly 95 percent.
And the last category act it two hundred percent.
So using burrito you can estimate how many of these categories contribute to how much percentage of
the total.
So for example if you would like to find all those important two or three categories which are counted
we contribute 80 percent of the total.
And you can do that using up burrito do analysis.
So this is how we create frequency distribution and histogram.
Good thing about using Excel is you do not need to create a frequency distribution table to create histogram
I told you how to do that.
So that you understand the concept being a histogram.
That's all for this value.