Three median line.

[Streaker]

No worries, cheers fellas.

[Streaker]

A bit off-topic, but would they ever give a transition matrix where the columns don't add up to 1? I've seen it plenty of times in NEAP exams.

[dahnnyz]

what's the m for

[_avO]

m is for gradient, however Ym and Xm represent 'middle section'

as for the transition matrix, i don't see why they wouldn't make it 1. I have seen negatives though

[summyx]

Does anybody know the way to to the median line on the TI 89?

[gamblor0]

no.
transaition matrix is like a pecentage, CANNOT be negative and CANNOT exceed 1.
and why am i still up when i have 2 exams tmrw?
lol

[Xavier1234]

If you have the gradient and at least one point on the line, why can't you just use y=mx+c to find the y-int?

because it gets shifted up or down 1/3 depending on where the middle median X,Y values are, so its not always accurate to do this method

Wait so just to confirm, the median-median function on my CAS is essentially the same as doing it manually (i.e. splitting the graph up into three sections and finding medians then plotting etc)

No it also automatically shifts the line 1/3 (as mentioned before) and makes an accurate calculation of the y-intercept

An alternate method is to find all 3 median coordinates, find the gradient and then use the formula I wrote a few posts ago

lol I keep forgetting that.

While we're at it, why is that necessary? Also how do they judge what 1/3 is?

its always gonna be an estimation of the 1/3 distance towards the median of the middle group. however, i think logic should just be applied as to how much 1/3 actually is. you guys are all smart you can do that!

[_avO]

can't rely on logic, when you are finding the y-int always use your calc

[linahh123]

can't rely on logic, when you are finding the y-int always use your calc

What if the exact co-ordinates aren't given and you're only supplied a graph with points?

[_avO]

What do you mean points? Isn't that the same as co-ordinates

[onerealsmartass]

so i know we can just chuck the data onto the CAS and draw our 3 median line acccording to that, but if we were to do it by hand how do we know how much 1/3 is?? <- as in how do we know how far we're suppose to move it?
thanks

[seltick]

the verticle distance from the middle point, estimate roughly

[onerealsmartass]

my text book says 'Mark in the medians and place a ruler on the outer 2 medians. maintaining the same slopw on the ruler, move it 1/3 of the way towards the middle median'
it also says that the arithmetic approach to finding the 3 median line gives a more accurate equation because the calculator just gives approximate values

[_avO]

Do the calculations, it's more safe and accurate (what if the y-int was 57 and the scale was in 10's, after estimating 1/3 would you know it was 57?)

[physics]

is the least regression line drawn based on the median points?