median lines (1 Viewer)

[lizzieee_]

can anyone please tell me how to draw a median line in a scatterplot graph? with how to find the midpoints and all....?

I know how to do a line of best fit and all, and usually when i get these questions I make it up, guessing which points and I get it right, but I lose marks cos I didn't show working. what working? I can't find it anywhere in my textbook

thanks dudes

 

[cro_angel]

ok well you need to divide all of your points into three sections.. evenly
if theres 10 then do it 3 | 4 | 3
if theres 11 then 4 | 3 | 4
if theres 12 then 4 | 4 | 4
you get the gist.. if they cant all be even make sure the two end ones are
then you need to find the median point out of every third of your scattergram.. if there are only three points then its obviously the second one but if there are 4 points then u need to find the average of the 2 middle points
so now you have one dot out of every third of your page.. when you rule a line through it make sure its 1/3 of the distance away from the point in the middle section and 2/3 away from the two points in the end sections.. and thats your median line of regression yay
i can draw a diagram if you dont really understand but yeh

 

[lilmzqt]

speaking of scatterplot graph thingys - how DO you do that line of best fit thingy - that doesnt make any sense to me so if sum 1 could help it would b much appreciated. thanx!

 

[PC]

Median Lines of Regression

There's a good little demo at hsc.csu.edu.au/maths, and follow the links to DA7 - Correlation. It's a very dull flash animation, but it's makes things quite clear.

 

[lizzieee_]

thanks heeeapps cro_angel that helps

hmmm.... line of best fit is just where you draw a line through the graph which shows the general direction the dots go in. theres generally two dots on the edges of the graph you can join up to make it.

 

[cro_angel]

yeh its putting a line through your graph with around about the same amount of dots on each side of the line
haha that flash thing was fun.. woops i got mixed up its 1/3 away from the 2 outer points not 1/3 from the middle point
sorry

 

[[Paul]]

Questions, does the line of best fit have to start in the bottom left hand corner? or can it start halfway across and then go up on an angle for a graph like this (number 2)

 

[cro_angel]

the line of best fit usually doesnt start in the bottom corner.. and often they ask you for an equation and where it starts on the y axis is where you get the +b from at the end of the equation
with graph number 2 the line would go down below the graph and the y intercept would be negative so its a -b in the equation

 

[caityboo]

can someone please explain how to find the equation of a median regression line???? hsc is tomorow and this is one of the many things i cannot work out!! thanks..