GMAT

Sub Topics

Understanding Bar Graphs And Pie Charts Summarizing Categorical Data Using Tables How to Calculate Percent Increase With Relative Cumulative Frequency Tables What is a Two Way Table Make Estimates And Predictions From Categorical Data What is Quantitative Data Definition Examples What is a Histogram in Math Definition Examples What Are Center Shape And Spread How to Calculate Mean Median Mode Range Describing The Relationship Between Two Quantitative Variables Reading And Interpreting Line Graphs Making Estimates And Predictions Using Quantitative Data z Test Formula Example Binomial Distribution Definition Formula Examples Range of Values Definition Overview Data Abstraction Definition Example Types of Statistical Analysis How to Draw a Trend Line How to Find The Equation of a Trend Line

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GMAT: Statistical Analysis With Categorical Data
How to Draw a Trend Line

After reading this how-to lesson, you'll learn how to take a somewhat random plot of points and turn it into a straight line that roughly follows the pattern of the points.

How to Draw a Trend Line

The Steps

In this lesson, you'll learn how you can draw a trend line when you are given what seems to be a random collection of points. This trend line is the line that approximates the behavior of your points. You can only draw a trend line if your points seem to follow a pattern such as this one:

Looking at this graph, you can see that your points seem to follow a pattern. They seem to be going upwards. Of course you'll have some points (the red and purple points) that seem to be way off from the others and this is normal when you perform real world studies. This particular type of graph is called a scatter plot because you have your points scattered on the graph. You can't simply connect the dots as it were to create a line. The dots don't line up neatly like that.

So, if your graph looks like it's following a pattern, then you can go ahead and draw a trend line for it. To do so, follow these steps.

Step 1: Locate the line that splits your data in approximately half. Your trend line approximates your data, so you'll want this line to be in the middle of all your data. Ideally, half of your points will be above your line and the other half will be below your line.

Step 2: Draw the line.

Once you've located the line that cuts through the approximate middle of your data, then you can go ahead and draw it.

The Solution

For the graph above, your trend line will look like this.

Counting your points, you count 5 points above and 6 points below. Your trend line is approximate so you don't have to have exactly half above and half below. As long as it's roughly half and half, you are okay.

Example

Let's try another example.

Draw the trend line for this graph.

Looking at this graph, you determine that you can draw a trend line since the points do seem to follow a pattern. They keep going up.

To draw the trend line, you look for a line that approximately cuts the data in half. You draw this line.

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This line looks like a good trend line because you can see that approximately half the points are above the line and half are below the line.

Drawing trend lines is a useful skill to have as this is something you'll need to do when working with graphs. In the real world, when you have real world data that's spread out like this, it makes it easier to work with the data when you have a trend line. A trend line lets you forecast and predict what may happen over time or in other situations that don't have data just yet. For example, if a scientist has some data points for the growth of a forest over time and this data can be approximated with a trend line, then the scientist can be use the trend line to show what will happen to the forest 10 years from now, 20 years from now, etc.