Notes/Examples for Eqation of Median-Median Line of Best Fit

A second, and more accurate, method of finding the line of best fit is the median-median method.

This method was created to handle large sets of data before calculators were widely available. However, it is programmed into our graphing calculators.

Steps to use median-median method: Graph the data 1. Split the data into three groups of equal size. If there is an extra point, give the middle group the extra point. If there are two extra points, give the outside groups an extra point each. 2. Find three summary points: find the median x value for each group find the median y value for each group 3. Plot and label each of the three points. Connect the first and last point with a line. 4. Determine the equation of this line, in slope-intercept form. Some people stop here, but to find the median-median line, there aer a few more steps. We need to draw a parallel line, 1/3 of the vertical distance towards the middle summary point. 5. Find the coordinates of the point on the line vertically below the middle point. We know the x-coordinate already. Just plug that into the equation and we will find the y-coordinate. 6. Determine the vertical distance between the two points. Determine the coordinates of the point taht is 1/3 of the vertical distance toward the middle summary point. 7. Find the equation of the new line of best fit (use parallel lines to find the slope and you have one point on the line).

Investigation -go through the investigation step by step as a whole class What is the advantage of using this method over the estimation method? What is the disadvantage of using this method over the estimation method?

Using Technology -go through the same question using the graphing calculators -write down the key strokes, step by step