By Subvertadown

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D/ST , Expectations , Quarterback , Understanding StatisticsThis post is about exploring how well projection models might improve the points we get from the QB position. Plus some commentary exploring how predictable/unpredictable QBs are.

Some key questions were:

What's different about QB compared to D/ST?

and "How much measurable improvement can be made to QB projections?"

I was looking for the the next best position for streaming, to extend my method kicker and D/ST projections. I now have a sense that more people are realizing how QBs are streamable, but when I considered all the comments and interpretations I've read, I thought it was important to address some of the presumption that QB is a "safe" position. The risk level should be something tested against D/ST, so I explore this below.

I also sense that QB projections may often made by "gut and experience" rather than stats. I'm not sure how true that is, but there are a number of anecdotal examples where I could see my older (primitive) model seemed better at deselecting top QBs. For example, the number of sites that listed "matchup-proof" Wilson at QB1 in week 15 of 2017. So, maybe common QB projections are not really optimized, and there is room for improvement.

Sometimes people say that QBs are safe and more predictable, whereas D/STs are less reliable. I claim this is not true, because **QB fantasy points fluctuate at least as much as D/STs**. Just look at this graph of score distributions for the two positions. Their shapes are not too dissimilar, differing noticeably by the center position.

So the QB point "floors" might seem higher just because the overall mean score is higher, but this fact alone should not create a difference in your FF strategy between the two positions QB and D/ST. (Excepting that rare decision to remove D/ST from your roster altogether. If D/STs were required to be rostered, then the QB and D/ST positions are similar in terms of risk.)

Sometimes it is also claimed that the "CV" (coefficient of variation) is lower for QBs, but please everyone realize that the **CV is a meaningless measure**, unless the point scale has an absolute zero. (Example: D/STs often go negative, and the CV would be infinite if a D/ST had a point average of 0. It's nonsense.) Instead, when comparing the volatility of different positions, you should only consider the degree to which variance affects your total roster score. In other words, just use deviation such as standard deviation, if comparing variation in QB vs. D/ST.

To emphasize the point that QBs and DSTs carry the similar amounts of risk, just look at this bar chart of seasonal standard deviations for the two positions. The bars are numbered from season average rank, so the leftmost bars show the standard deviation for QB1 and D/ST1. Clearly, the variance is similar: in fact, each individual QB's fantasy scores have a standard deviation of 7.3; for D/STs it is 6.4. So **individual QB scores vary at least as much as individual D/ST scores**, and this observation should influence whether you choose different strategies between the two positions.

On a weekly basis, D/ST projections and QB projections also have similar accuracies / inaccuracies. Described more below, the weekly QB projections have correlation coefficients around 0.35. For D/STs projections, the average week correlation was also about 0.35 - 0.40 (in 2018). So perhaps QBs are equally or more difficult (though I could imagine more accurate to project than D/STs when forecasting an entire season).

To stream or not to stream

When deciding whether a position can be streamed, these are some of the important factors:

Are the players' average scores similar, or

**is there a large drop-off?**Look at this comparison above, of the drop-off in season average, from the top ranked to bottom ranked. (QB scores are shifted down by 12 points for better visual comparison.) The drop-off for QBs is greater than it is for D/STs, which could be an argument against streaming if the amount is large enough. The gap from QB20 - QB2 is 5 points, compared to 3.5 points for DST20 - DST2. Is this extra**1.5 point difference**in gap enough to make streaming unattractive? Wait and see below.Does the fantasy score

**vary a lot with the opponent**, in a highly predictable way? For D/STs, it is often more obvious that the opponent is critical to the fantasy score. In fact, you can easily make a simple mathematical model yourself, to demonstrate this: use only each*opposing offense's*average historical "D/ST fantasy points allowed", and you will find that the D/ST's weekly score has good dependence on their opponent average (correlation 0.2). In contrast, each D/ST's*own*historical fantasy point average is much less predictive of each next-week's score (correlation 0.05). For QBs, the trend is exactly the reverse: Previous own average fantasy production is predictive (correlation 0.25) whereas "QB points allowed" is almost meaningless (correlation 0.03). I think this is one reason why QBs are considered predictable: past fantasy production indicates future fantasy production.Is this enough to conclude that QBs are more predictable? No, wait, there's more...! It turns out that QBs

**ARE**dependent on other parameters of their opponents-- just not on the abstract construct of "fantasy points". This is where I believe an improved model can make a difference. My updated models produce a projected std. dev. of 2.3 points for D/STs and 2.0 points for QBs, which is a measure of how much variance is predictable.

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