# Linear filtering trend line, Add Trend Lines to a Visualization

Content

Two-way tables Video transcript Shira's math test included a survey question asking how many hours students had spent studying for the test.

### Add Trend Lines to a Visualization

The graph below shows the relationship between how many hours students spent studying and their score on the test. Shira drew the line below to show the trend in the data. Assuming the line is correct, what does the line slope of 15 mean?

So let's see. The horizontal axis is time studying in hours.

## Interpreting a trend line (video) | Khan Academy

The vertical axis is scores on the test. And each of these blue dots represent the time and the score for a given student.

So this student right over here spent-- I don't know, it looks like they spend about 0. And they didn't do too well on the exam.

### Linear trend estimation

They look like they got below a 45, looks like a 43 or a 44 on the exam. And what Shira did is try to draw a line that tries to fit this data.

And it seems like it does a pretty good job of at least showing the trend linear filtering trend line the data. Now, slope of 15 means that if I'm on the line-- so let's say I'm here-- and if I increase in the horizontal direction by so there, I increase the horizontal direction by I should be increasing in the vertical direction by And you see that. Now, let's see which of these are consistent. In general, students who didn't study at all got scores of about 15 on the test.

Well, let's see.

### Interpreting a trend line

This is neither true-- these are the people who didn't study at all, and they didn't get a 15 on the test. And that's definitely not what this 15 implies. This doesn't say what the people who didn't study at all get. So this one is not true. That one is not true.

Let's try this one. If one student studied for one hour more than another student, the student who studied more got exactly 15 more points on the test.

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Well, this is getting closer to the spirit of what the slope means. But this word "exactly" is what, at least in my mind, messes this choice up.

You must also select the number of periods What type of Data A trendline is not always appropriate. It all depends on the type of data. Data that is appropriate for a trend line would be: Paired umbers which can be plotted on an XY Scatter Charts that have a Date category values assuming no gaps It is possible to add a trendline to a chart that has a Text category axis but it just wont mean anything A trendline is always associated with a particular data series It is possible for one data series to contain multiple trend lines Regression Analysis Regression Analysis is a form of statistical analysis which is used for forecasting. Regression Analysis estimates the relationship between variables so that a given variable can be predicted from one or more other variables.

This is just saying that this is the general trend that this line is seeing. So it's not guaranteed.

## Add Trend Lines to a Visualization - Tableau

For example, we could find this student here who studied exactly two hours. And if we look at the students who studied for three hours, well, there's no one exactly at three hours.

But linear filtering trend line of them-- so this was, let's see, the student who was at two hours. You go to three hours, there's no one exactly there.

You can publish a view that contains trend lines, and you add trend lines to a view as you edit it on the web. When you add trend lines to a view, you can specify how you want them to look and behave.

But there's going to be students who got better than what would be expected and students who might get a little bit worse. Notice, there's points above the trend line, and there's points below the trend line. Let's try this choice.

In general, studying for one extra hour was associated with a point improvement in test score. That feels about right. In general, studying for 15 extra hours was associated with website where you can earn money 1-point improvement in test score.

Well, no, that would get the slope the other way around. So that's definitely not the case. So let's check our answer. And we got it right.