@@ -30,7 +30,7 @@ where sum of ratings can be calculated either by, well, summing up all ratings o

OK, so that's the concept, but crucially that's not all the details. You still need to choose [i]how many[/i] dummy ratings you want to add and [i]what value[/i] they should take. Since People on the Internet™ who disagree with your ranking will try to manipulate it in whatever way they can, sites are usually very cagey about said details. [url=https://en.wikipedia.org/wiki/IMDb#Rankings]IMDb used to be more transparent[/url], [url=https://www.boardgamegeek.com/thread/103639/new-game-ranking-system]as was BGG[/url], but now we have to dig a little deeper.

Let's start from the easier of the two, the value of the dummy ratings. It is commonly chosen to represent some [i]prior mean[/i], i.e., some decent estimate of the rating a new game in the database would have. A frequent choice would be to use the average rating across [i]all[/i] games. It's a fair assumption – without further information about a game, we don't know if it's any better or worse than the average game. However, Scott Alden actually gave away the answer in that interview from the beginning: BGG chose the dummy value to be [b]5.5[/b]. Their rationale is that ratings range from 1 through 10, so 5.5 is the midpoint. Of course, people tend to rather play and rate much more the games they like, and so the average rating is around 7. Opting for the lower value here is part of the design of the ranking: it means a new game would enter the ranking rather at the end of the pack. On the other hand, using the mean as the dummy value means a new game is placed more or less in the middle. It is worth mentioning that IMBd does use the mean (or at least used to), but they only ever publish the top 250 movies, and don't care about the crowd behind.

Let's start from the easier of the two, the value of the dummy ratings. It is commonly chosen to represent some [i]prior mean[/i], i.e., some decent estimate of the rating a new game in the database would have. A frequent choice would be to use the average rating across [i]all[/i] games. It's a fair assumption – without further information about a game, we don't know if it's any better or worse than the average game. However, Scott Alden actually gave away the answer in that interview from the beginning: BGG chose the dummy value to be [b]5.5[/b]. Their rationale is that ratings range from 1 through 10, so 5.5 is the midpoint. Of course, people tend to rather play and rate much more the games they like, and so the average rating is around 7. Opting for the lower value here is part of the design of the ranking: it means a new game would enter the ranking rather at the end of the pack. On the other hand, using the mean as the dummy value means a new game is placed more or less in the middle. It is worth mentioning that IMDb does use the mean (or at least used to), but they only ever publish the top 250 movies, and don't care about the crowd behind.

The other value, the [i]number[/i] of dummy ratings, requires more work. Because some of the details and data are unknown, we cannot actually pin down the exact number that BGG is using. Instead, we'll try three different approaches, and compare their results.

@@ -48,7 +48,7 @@ where `sum of ratings` can be calculated either by, well, summing up all ratings

OK, so that's the concept, but crucially that's not all the details. You still need to choose *how many* dummy ratings you want to add and *what value* they should take. Since People on the Internet™ who disagree with your ranking will try to manipulate it in whatever way they can, sites are usually very cagey about said details. [IMDb used to be more transparent](https://en.wikipedia.org/wiki/IMDb#Rankings), [as was BGG](https://www.boardgamegeek.com/thread/103639/new-game-ranking-system), but now we have to dig a little deeper.

Let's start from the easier of the two, the value of the dummy ratings. It is commonly chosen to represent some *prior mean*, i.e., some decent estimate of the rating a new game in the database would have. A frequent choice would be to use the average rating across *all* games. It's a fair assumption – without further information about a game, we don't know if it's any better or worse than the average game. However, Scott Alden actually gave away the answer in that interview from the beginning: BGG chose the dummy value to be **5.5**. Their rationale is that ratings range from 1 through 10, so 5.5 is the midpoint. Of course, people tend to rather play and rate much more the games they like, and so the average rating is around 7. Opting for the lower value here is part of the design of the ranking: it means a new game would enter the ranking rather at the end of the pack. On the other hand, using the mean as the dummy value means a new game is placed more or less in the middle. It is worth mentioning that IMBd does use the mean (or at least used to), but they only ever publish the top 250 movies, and don't care about the crowd behind.

Let's start from the easier of the two, the value of the dummy ratings. It is commonly chosen to represent some *prior mean*, i.e., some decent estimate of the rating a new game in the database would have. A frequent choice would be to use the average rating across *all* games. It's a fair assumption – without further information about a game, we don't know if it's any better or worse than the average game. However, Scott Alden actually gave away the answer in that interview from the beginning: BGG chose the dummy value to be **5.5**. Their rationale is that ratings range from 1 through 10, so 5.5 is the midpoint. Of course, people tend to rather play and rate much more the games they like, and so the average rating is around 7. Opting for the lower value here is part of the design of the ranking: it means a new game would enter the ranking rather at the end of the pack. On the other hand, using the mean as the dummy value means a new game is placed more or less in the middle. It is worth mentioning that IMDb does use the mean (or at least used to), but they only ever publish the top 250 movies, and don't care about the crowd behind.

The other value, the *number* of dummy ratings, requires more work. Because some of the details and data are unknown, we cannot actually pin down the exact number that BGG is using. Instead, we'll try three different approaches, and compare their results.