This seems to be one of the big questions heading into next season. Does Ellis hurt the team by taking more shots? As Curry gained influence and control of the team, did Ellis back off? Did his efficiency go up? What about useage? I was really curious to look into the stats a bit deeper and see what I could see. So, I went to bball-reference.com and started crunching a few numbers. Specifically, I looked at three measures (TS vs. USG), (TS vs. Game #), and (USG vs. Game #). Game # is exactly what it sounds like (i.e. Game 1 is the first game of the season, 82 is the last). By plotting against game #, we can see temporal correlations. Here are the formulas, for reference:
(TS) True Shooting Percentage; the formula is PTS / (2 * (FGA + 0.44 * FTA)). True shooting percentage is a measure of shooting efficiency that takes into account field goals, 3-point field goals, and free throws.
(USG) Usage Percentage (available since the 1977-78 season in the NBA); the formula is 100 * ((FGA + 0.44 *FTA + TOV) * (Tm MP / 5)) / (MP * (Tm FGA + 0.44 * Tm FTA + Tm TOV)). Usage percentage is an estimate of the percentage of team plays used by a player while he was on the floor.
Here are the data (for 2009-10 obviously):
There are many interesting trends (and non-trends). For example, there appears to be a greater trend (positive correlation) for Ellis' TS vs. USG compared to Curry. Therefore, Curry's efficiency tended to be more independent of his USG. Ellis tended to shoot better when his USG increased. This actually tells me that it is not necessarily the case that Ellis will shoot better (i.e more efficiently) if his role in the offense is diminished. Indeed, according to the data, he may shoot worse.
Some on this site have said that Ellis "backed off" (my paraphrasing) his shot-taking as Curry's influence began to grow. Well, let's take a look at the data. We can see by Curry's USG vs. Game # plot, that Curry's USG clearly increased as the season progressed. So, the question to ask (in my mind): Did Ellis' USG go down during the season? The answer is clearly NO. There doesn't appear to be any trend in Ellis' USG vs. Game #. What about Ellis' TS vs. Game #? Again, the answer is NO, there was no relation.
Some questions to think about... Why is Ellis' TS correlated with USG, whereas Curry's does not appear to be? Is it that Ellis adjusts his role in the offense when he's "feelin' it"? Does he take fewer shots when he's having an off-night? Or, perhaps, is it that Curry is getting Ellis the ball more when he sees that Ellis is shooting well? There are a lot of factors here obviously. What I've presented is only a starting point. But I think that by looking into these kinds of per-game data, it may be possible to tease out some answers, or at the very least, ask some interesting questions. Feel free to suggest some other comparisons, or provide your own below!
UPDATE: I performed a regression analysis using the function "regress()" in MATLAB (click on the link for gory details). The results are shown below. It looks like the numbers I previously put for R^2 values were actually the coefficients of the fit. It turns out the p-value for Ellis' TS vs. USG (p=0.061) is just above what would normally be considered statistically significant (p<0.05). The p-value for Curry is well above at ~0.8. Therefore, while the data for Ellis do not show statistical significance, I do think it is reasonable to call the correlation a "trend", albeit arguably weak.