Re-thinking the Goal Differential Bonus

Tim Braun pointed out something on USCHO’s Fan Forum that I hadn’t fully considered:

Is it just me or does it seem strange that MTU gains 25 points for taking 3 points from a superior BELOW team, but that same team gains 43 for sweeping an inferior team?

Other than the way MSU did it against LSSU, I don’t think anyone would be more impressed with MSU’s sweep of LSSU than MTU’s 3 points vs MSU?

He’s right.  In thinking about it, a goal-differential of 3 seems to be decisive.  Limiting things to a goal differential of 2 would leave me going into the box scores to seeing if there’s an empty-net goal that makes it a wider margin.  Even if there’s an ENG in a 3-goal game, the game was already pretty decisive.

Going forward: I’m capping the goal-differential bonus at three goals, regardless of outcome.  I explain my reasons why below after looking at the data.  When I re-calculate BELOW going forward based on results alone, this cap will have an effect.  BELOW gains/losses in the first list of ten games will be adjusted appropriately, and as such the ratings will change slightly.

How often are there three-goal margins?

I decided to look into how many times a goal margin exceeded three goals in the 2015-16 WCHA.  We would presume that these wide margins would come in games where BELOW was ranking one team well above the other, with the better team getting the big win.

Let’s look at the data.  Matchups in bold are situations where a wide margin benefits the lower BELOW team; matchups in italics are big road victories.

  1. Game 1: Michigan Tech (1654) beats Ferris State (1481) by a 5-1 margin.
  2. Game 13: Alabama-Huntsville (1391) beats Lake Superior (1389) by a 5-0 margin.
  3. Game 32: Alaska-Anchorage (1450) upsets Ferris State (1566) by a 5-0 margin.
  4. Game 49: Minnesota State (1708) beats Alaska-Anchorage (1481) by a 6-2 margin.
  5. Game 66: Michigan Tech (1551) beats Lake Superior (1490) by a 6-2 margin.
  6. Game 80: Bemidji State (1520) beats Alaska-Anchorage (1458) by a 5-1 margin.
  7. Game 89: Bowling Green (1645) beats Alaska-Anchorage (1430) by a 6-2 margin.
  8. Game 90: Bowling Green (1661) beats Alaska-Anchorage (1414) by a 6-2 margin.
  9. Game 91: Minnesota State (1670) beats Lake Superior (1472) by an 8-0 margin.
  10. Game 93: Minnesota State (1687) beats Lake Superior (1455) by a 5-0 margin.

So of those 10 matchups, only one — Anchorage going into Big Rapids and shutting the Bulldog down 5-0 — was what you’d term an upset.  The Huntsville win over Lake State was surprising, but you’ll always get one outlier in a season’s worth of games. (Given that UAH has won just four games to-date, I’d call that an outlier.  Please give me a minute to pull myself together.)

The road rout by Tech over Lake State isn’t a big shock, as the Taffy Abel isn’t a huge home-ice advantage, and the trip across the UP is one of the shorter ones in the WCHA.  The big Bemidji win in Alaska was, as we’ve noted, indicative of a big turn for the Beavers as 2016 has started.

In light of the above, it makes sense that goal-differential should be capped.  As such, I have a nice IF statement in my table: if the goal differential is greater than 3, the goal differential bonus is capped as if the margin were only 3.

What about margins of three goals — how many are two-goal games that became three-goal games?

For completeness, the below 3-goal games had empty-net goals that padded their outcome:

  1. Game 19: Ferris State v. Minnesota State.
  2. Game 41: Bemidji State @ Alabama-Huntsville (and it wasn’t even the final goal; the Beavers later scored 5×5).
  3. Game 44: Bemidji State @ Alabama-Huntsville.
  4. Game 46: Michigan Tech @ Alaska.
  5. Game 64: Bowling Green @ Bemidji State (ENG SHG to boot).
  6. Game 68: Alabama-Huntsville @ Minnesota State.
  7. Game 97: Michigan Tech @ Bowling Green.

Games 3, 12, 22, 26, 31, 74, 76, and 84 have “true” three-goal wins, or eight of the 15 wins.

To recap:

  1. 25 WCHA games through 98 played have margins of three goals or higher.
  2. 10 of those games have margins greater than three goals.  For purposes of calculating BELOW, they will be treated as if they were three-goal victories.
  3. Of those ten games, only one can truly be considered an upset, while another was a 50-50 matchup.  As such, three goals is where we draw the line.
  4. Of the 15 remaining games, eight were three-goal margins unaffected by empty-net goals.
  5. Of the remaining seven games, six ended in empty-net goals.
  6. That last game is when Huntsville gave up an ENG with :43 left and then another goal with :08 left and the goalie in the net.  Ladies and gentlemen, your 2015-16 UAH Chargers.

We may re-visit this three-goal cap in the offseason, but I’m willing to bet that we’ll see similar data from the previous two seasons.

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