My last post was in September and was entitled “I am tired so tired.” That ended up prophetic because with the fall break I ended up not posting for three weeks. Whew. I needed that break to get back on track and then caught up. I am glad I have my head on right now and am refocused.
So, on to new posts.
Today, Eli Luberof posts on Twitter:
— Eli Luberoff (@eluberoff) October 21, 2014
This just made my day. Now I can do data entry, just make sure to use the subscripts on the data points and the variables. Notice that you can do different forms of the equations! You can do yhat = a + bx or you can do yhat = mx + b. Either format gives you the r value and the residuals.
Go residual plots! That is awesome in and of itself. I am in love. Right now, the only thing that kind of saddens me is that I can not use “height” and “time” as variables. Desmos needs the x_1 and y_1 format to work. That is sad, because in stats we try to use words as variables. Oh well. At least this gives me a clean, nice, clear way to teach this topic to all classes.
Eli, two thumbs way up for this addition. [And just as an aside to the rest of the #MTBoS to show how responsive Eli is to us. He did a small focus session at #TMC14 with several stats teachers and asked us how we would want to do this. He told us he had not thought about residuals at that time, so to see residuals so easily pop up here was very exciting. Desmos is truly responsive to teachers needs.]
Edit: Okay, so I kept playing and tried to build a lesson with it on residuals. Found some interesting things that I like and don’t like.
I tried to calculate the predicted values, the yhat. Desmos didn’t like merging the algebraic with the regression. Not at all. This is what I got when I tried:
I would like to have the ability to show not just the actual value, but also the predicted value. That way I can show where the residual actually comes from. Beggars can’t be choosers though.
Edit again: Desmos comes through like a champ. They tweeted this out to me last night.
Which led me to do this:
Click on it and look at it large. You can see how I used a function per Desmos’ advice to then calculate the residuals instead of just using what is given. This pretty clearly shows where those points at the bottom come from.
I am teaching residuals right now in AP Stats, and I will use this as a demonstration (if it is up long enough) to show what the calculators are doing. Too often the learners don’t think beyond the buttons and just mechanically find the resid plot without thinking about what is going on.