Until now, we’ve normalized our data by time. This means we’ve been reporting out stats on a “per X minutes” basis. Today, we’re going to unpack a little bit about why we normalize and why we might not always want to normalize by time in the context of the NBA. What is “normalizing”? Normalization is the act of putting different observations on a level playing field. (That’s not literally what Wikipedia says, but I think it’s a fair paraphrasing for our application.
Previously on DIY Metrics, we did some remedial cleaning on the full 17-18 play-by-play data set. Today, we’re going to take that clean data, generate full-season five-man plus/minus numbers, and then do some plotting! Cleaning, again So, turns out there were a few bugs that I didn’t catch the first time we went through the cleaning process. This is fairly typical in my experience: You’ll go through your data cleaning and think everything is Gucci only to find once you start your analysis that there are irregularities or issues you hadn’t considered.
So I finally broke down and got a full season’s worth of NBA play-by-play data to work on. Going forward, I’ll be using the full 2017-2018 play-by-play data from NBAstuffer. To date, I’ve been building my scripts using functional programming with the goal of having each step easily work with new data sets. This will be a good test of whether I’ve been successful! But before we do that, we need to look at the new data set and see what, if anything has changed.
This is an update to my Analysis Philosphy page, which is still working towards completion I only get 1,750 hits on Google when I search for “Distributionality”, so maybe I should clarify what I mean, though I don’t think it’s anything profound. That data follow distributions is a tautology. When this doesn’t appear the case, it means we’ve failed to properly model hte data generation function. The most typical failure mode is to assume that the distribution is simpler than it is.
Last time on DIY Metrics, we calculated five-man-unit plus/minus ratings from scratch. If we want to use measures like this to compare performance for these groups of players, its important to consider how much game time we have for each unit. There’s a relevant discussion to be had about whether “number of posessions” or “elapsed time” is the best way to compare these groups, (IMO, it depends on what specific question you’re trying to answer with your metric) but today we’ll avoid that discussion and normalize over time because it’s easier.
I mean the term of art, not the concept or field of study. And what’s dumb is how it’s applied. “Machine learning” is also dumb in a similar way. Some definitions for AI You can go back to the beginning if the field if you want to, but modern definitions tend to to be vague. There are good definitions out there, but these sound esoteric and unless you’re really interested in defining AI precisely, you’ll probably just stick with Merriam-Webster or Wikipedia, which means literally:
Last week, I described how to build a plus/minus score for individual players based on data from NBAstuffer. I enjoyed walking through that process, so lets continue the series and expand our focus. Five-man units vs. Individual Players One of the first things I talked about on this site was comparing different metrics and choosing the right one for the task at hand. Plus/minus for individual players is a weird metric, because it’s taking a team outcome (net change in score) and applying it at an individual level.
So this is a blast from the past. NC State (at least while I was there) did something interesting for their prelim. Instead of taking another test like we had to do at the Masters level, they gave all their students a subject unrelated to their research, and had them write a lit review and do a small simulation study. My topic was local polynomial smoothing. I don’t think I did a particularly good job, but afterwards, I posted it on my NCSU website as an example of things I’d written.
In order to better understand some “advanced metrics”, I figured it’d be useful to build them from scratch. (This is also just a fun exercise in data manipulation, cleaning, etc.) For starters, let’s do something easy, namely raw plus/minus. For the code below, I’m using the free example play-by-play data set from NBAstuffer. They seem reputable, though I do have concerns about how widely-used their formatting is; one of the challenges with building a workflow is ensuring that the structure of your incoming data won’t change.
This is a post about communication. One of the through-lines of my academic and professional career is conflict between entrenched subject matter experts (SME) and hot-shot quantitative analysts. As a young undergraduate, I followed Baseball Prospectus Fangraphs through the SABRmetric revolution. I watched Nate Silver bring data-driven prognostication to the world of political journalism which had previously (and arguably still is) dominated by punditry. In my current job, I work with experienced analysts who have often been working on the same systems for years.