#Fancystats Friday: Applying stock market analysis to St. Louis Blues stats

It all started with this tweet in which I proclaimed the St. Louis Blues were an average team.

near 50% scf with low variability between games just reinforces my belief the #stlblues are just an average team https://t.co/AQdysvT7Yh

— Robb (@robbtuftshockey) January 13, 2016

Hockey analytics guru Steve Burtch took exception to my statement and a brief exchanged followed.  I argued that even if they are still above 50% they are trending downward and it would be nice to figure out when or if this downward trend will reverse.  Then @petbugs13 who writes for Canucks Army chimed in with this interesting thought

@robbtuftshockey @SteveBurtch probably techniques from stock analysis could help. Say, when 5 game ave crosses 20 game ave, etc.

— nobody (@petbugs13) January 13, 2016

I pulled the data from War on Ice and put together 6 different charts with what I would consider key metrics for team performance in a game:  corsi for, fenwick for, scoring chances for, goals for, team save%, team shooting%.  There are three trend lines for each stat and the trend is by game.  The gold line is the actual stat for that game.  The light blue line is the short term trend (5 game moving avg) and the dark blue line is the long term trend (20 game moving average).

When moving averages are used to analyze stock performance they are looking at the relationship between the daily price of a stock, the short term trend, and the long term trend.  This is from the website Investopedia

Another method of determining momentum is to look at the order of a pair of moving averages. When a short-term average is above a longer-term average, the trend is up. On the other hand, a long-term average above a shorter-term average signals a downward movement in the trend.

Moving average trend reversals are formed in two main ways: when the price moves through a moving average and when it moves through moving average crossovers. The first common signal is when the price moves through an important moving average. For example, when the price of a security that was in an uptrend falls below a 50-period moving average...

So in our charts, we will be looking at the relationship between the 5 game moving average, the 20 game moving average, and how the game trend crosses over those moving averages.

The Trends

We can see that a stock market analysis of a team's metrics during the course of a season isn't a perfect match.  In the case of stocks, they are looking at 20 and 50 day moving averages.  For an NHL team, 20 data points is roughly 25% of the season and 50 data points is over half the season.  We don't have the luxury of all those data points.  We are using 20 games and 5 games for our analysis.  As a result, the game by game trend crosses our moving averages quite a bit.  But that doesn't mean this type of analysis will not work.  We can still use the 5 game and 20 game moving averages to determine the momentum for each of the stats using the criteria from Investopedia.

The top two charts are possession and in both of those charts the short term trend (5 game moving average) is underneath the long term trend (20 game moving average).  This indicates that the Blues are still on a downward trend in regards to their 5v5 possession numbers.  The Blues are known as a heavy, possession team, but the way they are playing is slowly and surely chipping away at this reputation.  So based on this analysis, the Blues are still in a downward trend in regards to possession metrics.

The next two charts relate to scoring.  The long term trend for scoring chances for is hovering right at the 50% mark while the short term trend is hovering right below it.  It looks like it might want to cross over, but with the past few games below 50% the short term isn't crossing over soon.  On the other hand, the long term trend for goals for has been below 50% for the past several games and is slowly trending upwards to cross that 50% mark.  The sort term trend has even crossed the long term.  However, and this is a big however, the goals for data points have a large variance.  The data points can fall anywhere between 100 and 0 for a team at 5v5.  In other words, while this might look like a good omen, it isn't a very reliable indicator of momentum.  If the three other trends we looked at were heading upwards I would put more stock in the goals for momentum.  But as it is right now, the goals for momentum could be the result of lucky bounces or a Tarasenko breakaway.

Finally, the bottom two charts looks at the ultimate results of all the above stats.  The y axis for the team save % chart starts at 72%.  The momentum for team save % looked promising.  The short term trend was riding above the long term trend.  However, the last few games saw a crossover.  I know what you all are thinking and don't say it.  This is as much on the team as it is on the goaltender.  There are very few goaltenders that can overcome their team's sub 50% possession numbers.  Elliott is a solid goaltender, he isn't superman.  There is one bright spot in all this negativity however.  There is positive momentum for the team's shooting percentage.  The long term trend has been beneath the team's average.  In the last few games, the short term trend has cross the long term trend indicating upwards momentum.  However, as we mentioned above with the goals for trends, a lucky bounce and a Tarasenko breakaway can help boost that shooting % just like it does the goals for percentage.  At least it is upwards momentum and could be something to build on.

Conclusion

The future for the Blues does not look positive.  If they were a stock, I would advise you to sell ASAP or at least hold on to it until the momentum changes.  However, it looks like this team's momentum isn't going to be changing anytime soon.  I'll let you all fight it out in the comments as to whether or not this is on the coach, the players, or bad luck.  I look forward to reading your thoughts.