Define a scattergraph .

A scattergraph plots pairs of data, with each axis representing one of the two quantities being measured. Each pair is plotted as a single dot, and the dots are not joined up.

What does a line of best fit show on a scattergraph?

It shows the overall direction of the data, as a straight line drawn through the plotted points. It represents the best estimate of the relationship between the two quantities.

In this exam do you have to draw the line of best fit yourself?

No, the line will be drawn for you on the scattergraph. Your job is to find its equation , and then to use that equation to estimate further values.

Where do the coordinates of the two points used for the equation come from?

They come from two points lying on the line of best fit , not from any two plotted data points. The question may give them to you in context, or you may have to read them off the grid.

True or False? A value found from the equation of a line of best fit is only an estimate.

True. The line is itself only a best fit to the data, so any value taken from it is an estimate rather than a recorded fact. It is worth saying so in your answer, since the question asks what the data suggests rather than what actually happened.

National 5MathsSQAFlashcardsStatistical SkillsScattergraphs & Linear Models

Scattergraphs & Linear Models (SQA National 5 Maths): Flashcards

Exam code: X847 75

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FrontLine of Best Fit
Define a scattergraph.

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Cards in this collection (8)

Define a scattergraph.
A scattergraph plots pairs of data, with each axis representing one of the two quantities being measured.
Each pair is plotted as a single dot, and the dots are not joined up.
What does a line of best fit show on a scattergraph?
It shows the overall direction of the data, as a straight line drawn through the plotted points.
It represents the best estimate of the relationship between the two quantities.
In this exam do you have to draw the line of best fit yourself?
No, the line will be drawn for you on the scattergraph.
Your job is to find its equation, and then to use that equation to estimate further values.
Where do the coordinates of the two points used for the equation come from?
They come from two points lying on the line of best fit, not from any two plotted data points.
The question may give them to you in context, or you may have to read them off the grid.
What do you do once you have two points on the line of best fit?
Find the gradient between them, then use $y - b = m (x - a)$ in the usual way.
This is the same method used for any straight line, so nothing new is needed beyond identifying the two points.
Why might the equation of a line of best fit not be written in terms of $x$ and $y$ ?
The question defines its own variables, and the equation must be written using those.
With time $T$ on the horizontal axis and number of breeding pairs $N$ on the vertical axis, the answer is given as $N = 2 T + 4$ .
A line of best fit has equation $N = 2 T + 4$ , so complete the estimate of $N$ when $T$ is $9$ .
$N = 2 \times______+ 4 =______$
The completed estimate is:
$N = 2 \times 9 + 4 = 22$
Substituting the value of the horizontal variable into the equation is the whole of the method.
True or False?
A value found from the equation of a line of best fit is only an estimate.
True.
The line is itself only a best fit to the data, so any value taken from it is an estimate rather than a recorded fact.
It is worth saying so in your answer, since the question asks what the data suggests rather than what actually happened.

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