Original subtitles

Instructor: The most common graph used

to represent numerical data is the histogram.

First, we'll learn how to create it,

and then we'll provide a description

of the way the data is represented.

We are going to use the frequency distribution table

from our previous example to help us out.

Here it is.

As you can see, it looks like a bar chart

but actually conveys very different information.

As in the bar chart,

the vertical axis is of numerical type

and shows the absolute frequency.

This time though, the horizontal axis is numerical too.

All right, so each bar has width equal to the interval,

and height equal to the frequency.

Notice how the different bars are touching.

This is to show that there is continuation

between the intervals.

Each interval ends where the next one starts.

In the bar chart,

different bars represented different categories,

so the bars were completely separate.

Okay, sometimes, it is useful to plot the intervals

against the relative

rather than the absolute frequency.

As you can see,

the histogram looks the same visually

but gives different information to the audience.

Remember, relative frequency is made up of percentages.

There is no way to do that in Excel

but is a useful piece of information.

There is one last thing to note here.

We may create a histogram with unequal intervals.

An example is designing age groups.

You've likely completed some survey

where you were asked about your age

and the possible answers were 18 to 25,

then 26 to 30, 31 to 35,

and so on until 60 plus.

Clearly, the interval widths vary

and reflect different focus groups

for the experiment at hand.

An explanation for the choice may be

young adults under 25 cannot afford the product,

while adults over 60 have no interest in the product.

In any case, you should be quite experienced

to accurately design and interpret such groups.

It is highly recommended

that you stick with the equal width intervals

until you gain enough experience.

Okay, great.

This is how we can build a histogram

in order to represent numerical data.

Thanks for watching.