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### Course: Get ready for AP® Statistics > Unit 3

Lesson 2: Estimating with trend lines- Estimating the line of best fit exercise
- Eyeballing the line of best fit
- Estimating with linear regression (linear models)
- Line of best fit: smoking in 1945
- Estimating slope of line of best fit
- Estimating equations of lines of best fit, and using them to make predictions
- Equations of trend lines: Phone data

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# Estimating the line of best fit exercise

The "line of best fit" is a line that shows the pattern of data points. If we can find a good line, it means there is a linear trend. If not, it means there is no linear trend. We can't ignore points that don't fit the trend. Created by Sal Khan.

## Want to join the conversation?

- Khan Academy makes it a lot easier to understand some of the difficult math tasks.(13 votes)
- And it helps confuse you with the easier math tasks!(27 votes)

- i am lost. when i do it on the practice, i am usually wrong by one or two points. is there a way to calculate this??halp!(12 votes)
- Here's a process you might try. Find the point that is the closest to one corner. Then, find the point that is closest to the opposite corner. Connect those two points.

Then, look at the line you draw and compare the rest of the points to it. If there are more points above the line than below it, then you might need to move the line up some. And if there are more points below the line than above, you might need to move the line down some.

Just experiment until you've got the line as close as possible to as many points as you can. It's OK if some points are far away, as long as your really close to most of the points.(11 votes)

- so if i just do a line that is close to the other scatter points would it be right?(4 votes)
- A tip my teacher gave us was that a good line of best fit maintains a roughly equal amount of points on both sides.(6 votes)

- How do we make predictions in scatterplots(5 votes)
- Pretty sure it has something to do with the unit rate(maybe)(3 votes)

- Can you have a line of best fit when you have no correlation?(5 votes)
- If the correlation is exactly 0, then the best fit line using least squares regression is the horizontal line (slope 0) through y-bar (the mean y-value).(3 votes)

- Honestly, I still don't get it. How would you know if it's accurate? And there's a method called Least Squares to find the equation, but how would you calculate if there are hundreds of points?(4 votes)
- If there are hundreds of points you not be using a line graph, you should be using a f/x table (frequency table)(2 votes)

- What does best line fit mean(4 votes)
- its the imaginary linear line that would go best in-between the points to show how good of a fit it is(1 vote)

- I don't get what they mean by line of best fit? Can someone explain that to me, please?(2 votes)
- It means that a line that best represents a situation or problem(4 votes)

- i thought d line was meant to divide the points into equal parts(3 votes)
- A line of best fit is used to show a trend between points. For example, dots at (3,5),(6,6),(7,8) can have a line run through their main path that they look like they head towards. Not all lines of best fit hit all the points. Most don't. To summarize, the line of best fit is there to show the general positive, negative, or non-existent trend of the point.(2 votes)

- This is still really confusing and i have a test tomorrow on this :D(3 votes)

## Video transcript

Find the line of
best fit, or mark that there is no
linear correlation. So let's see, we have
a bunch of data points, and we want to find a
line that at least shows the trend in the data. And this one seems
a little difficult because if we ignore these
three points down here, maybe we could do a line that
looks something like this. It seems like it kind of
approximates this trend, although this doesn't
seem like a great trend. And if we ignored these
two points right over, we could do something like
maybe something like that. But we can't just
ignore points like that. So I would say that
there's actually no good line of best fit here. So let me check my answer. Let's try a couple
more of these. Find the line of best-- well,
this feels very similar. It really feels like there's
no-- I mean, I could do that, but I'm ignoring
these two points. I could do something
like that, then I'd be ignoring these points. So I'd also say no good
best fit line exists. So let's try one more. So here it looks like there's
very clearly this trend. And I could try to fit it a
little bit better than it's fit right now. So it feels like something
like that fits this trend line quite well. I could maybe drop this
down a little bit, something like that. Let's check my answer. A good best fit line exists. Let me check my answer. We got it right.