In statistics, a histogram and a curved line graph are both ways to display a given set of numerical data on a chart. The data must be discrete and continuous. However, both the histogram and line graphs have different properties and characteristics that must be understood.
What is a Histogram?
A histogram is a graphical representation of a set of data that displays data values in a specified range. It can also be described as a frequency distribution that shows how often a certain value occurs in a given set of data. Histograms are quite popular and widely used because:
- They can be easily interpreted
- They can easily compare data
- They work well with a large range of data
Histograms are inconvenient in the following scenarios:
- When multiple categories are present in the data
- When you need to find out the amount of input in the data set (For example: how many people the survey was conducted on)
What is a Curved Line Graph?
A curved line graph is another way to display the given numerical information on a chart. It basically denotes the change that has taken place over time in a given set of data. The curve bends upwards or downwards to show a trend in the data set. A curved line graph is a convenient statistical representation when:
- You want to highlight changes in one variable for constant values of the second variable
- You want a quick analysis of data
- You want to make a prediction of future values in the data set
However, curved line graphs have some limitations, which are mentioned as follows:
- The intermediate values between two points may be misleading
- Difficult to draw and interpret for data above 50 values
How to Draw a Histogram and a Curved Line Chart Together
In this section, we will show you how to combine a histogram and a curved line in a chart. If you are a beginner, knowing how to draw them together is essential.
Consider the following example for explanatory purposes:
Worked Example – Men and Sports:
A survey was conducted amongst 50 men aged 16 to 74 years. They were asked if they participate in a sports activity at least twice a week. The following table shows the results that were obtained from the survey:
Percentage of people who participated in sports at least twice a week
16 – 24 years
25 – 34 years
35 – 44 years
45 – 54 years
55 – 64 years
65 – 74 years
Over 75 years
Step # 1: Construct a Histogram Using the Data Given Above on a Chart
Using Microsoft Excel, the chart function in Microsoft Word or manual sketching, display the information in the form of a histogram like this with age group on the X-axis and percentages on the Y-axis. The resulting graph must look something like this:
Step # 2: Mark the Midpoints of Each Bar in the Histogram on Your Chart
Before you proceed to sketch or insert a curved line graph on this chart, you must mark the midpoints of each bar in the frequency distribution like this:
These mid points can be drawn manually if you are displaying your information on a hard copy chart. If you are working with Excel or Word, you may skip this step.
Step # 3: Join the Midpoints and Draw a Curved Line Graph on the Chart
If you are working on a physical drawing, it is time to take out your artistic guns! Using a sharp pencil, join each midpoint with the next one, starting from the very first bar in the histogram. The end result should look something like this:
And there you have it! The sharp, black line that passes through all the midpoints is your curved line graph drawn along with the histogram on the same chart!
If you are working with charts on Excel or Word, you can entirely skip steps 2 and 3 and do the following after Step 1:
- Click on the chart plot area of your histogram and select “layout” from the toolbar on top of your screen.
- On the far right, you will see an option that says “Trendline.” Click on the drop down menu with that option.
- It will show 4 different styles of trend lines as well as “more trendline options” to choose from.
- Select the trend line that matches the best with your data by clicking on it. For our worked example, we will select “exponential trend line.”
- And done! A curved line graph will be added to your histogram on the same chart, and your chart will look like this:
It is not always easy playing with statistical information. Sometimes, you have to undertake difficult tasks with complex functions in order to represent the given numerical data set. We hope you have now understood how to combine a histogram and a curved line graph in a chart for a given set of data, whether it is on Microsoft Excel, on Microsoft Word or on a manual graph sheet.
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