The Bruins have not scored a goal at 5 on 4 in 6 games now, and only 2 in their last 10. Should you begin to panic, or in this a normal goal drought? Using some basic statistics, we can determine whether or not there is a significant change in how the powerplay has performed over the last 10 games.
A quick stats primer:
- Mean is the average. It is all of the samples added together and divided by the number of samples.
- Standard deviation is what it sounds like. It is a measure of how far samples are from the mean. A large standard deviation means there is a large spread in the data.
I first went ahead and found significant statistics in 10 game spans this season. Those being: shots attempted, shots on goal, expected goals, and goals. Those were all set to a rate of 60 minutes.
I then found the mean and standard deviations of the 10 game samples for each stat. For instance, the mean 10 game goals per 60 is 7.11.
Once I have these two numbers, I can find upper and lower bounds of statistical significance. Using the empirical rule, we can assume that 95% of data should fall within 2 standard deviations of the mean. The other 5% are rare.
In the last 10 games, the Bruins shot attempts per 60 was -.02 standard deviations from the mean. In simpler terms, they’ve been shooting at their normal rate. Shots on goal per 60 and expected goals per 60 were .98 and .62 standard deviations away from the mean respectively. That means they have been slightly better in those metrics, but nothing of significance.
When it comes to goals per 60, however, they fall -1.63 standard deviations from the mean. Although it is certainly striking compared to shots and expected goals, it is not significant. The lower bound of significance is 1.09. Since 2.21 (the bruins goals per 60 the last 10 games) is greater than 1.09, it is not statistically significant. In fact, it’s not even the worst 10 game stretch for the Bruins. That occurred after the 21st game where the rate was 2.08.
The current powerplay drought for the Bruins isn’t something to worry about. There ability to produce shots has been fine, and their lack of goals is not significant enough to cause worry. If you look through the video, I’m sure you could pick out some differences in the powerplay that shots cannot tell you, but hockey can be random at times. At some point in the near future, the Bruins will be back to scoring on the powerplay again.