Lines-Of-Best-Fit gcse Edexcel

Lines of Best Fit

What is a line of best fit?

• If a scatter graph suggests that there is a positive or negative correlation

  • a line of best fit can be drawn on the scatter graph

    • This can then be used to make predictions

How do I draw a line of best fit?

• A line of best fit can often be drawn by eye

  • It is a straight line (use a ruler!)

  • It must extend across the full data set

  • There should be roughly as many points on either side of the line (along its whole length)

  • The spaces between the points and the line should roughly be the same on either side

• If there is one extreme value (outlier) that does not fit the general pattern

  • then ignore this point when drawing a line of best fit

What is the double mean point?

• A question may talk about the double mean point

  • This is the point

    • is the mean of the data values that are plotted along the x-axis

    • is the mean of the data values that are plotted along the y-axis

  • The question may give you the values of and

    • Or you may need to calculate the means from the data

• If a question mentions the double mean point, then the line of best fit must go through the double mean point

  • It should still follow all the other rules for drawing a line of best fit (roughly same number of points on each side, etc.)

• If a question doesn’t mention the double mean point

  • then you don’t need to calculate it or worry about drawing the line through it

How do I use a line of best fit?

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