Analysis - Suji Before vs After Riichi

Glancing through Riichi Book 1, I noticed a footnote that said people were a bit divided on whether suji before riichi was more dangerous than after or vice versa. Let's throw another data point into the ring.

Methodology / Disclaimers

• 1.5 million Houou hanchan games
• This data is a bit more meta-reliant than usual. If people sakigiri more or less often, it would change these.
• This data is from people who called riichi on discards 7~10, which seems relatively average.

First, let's look at the data for late tile discards.

Click to enlarge.

The number at the start of the row is how many tiles before riichi it was. -1 means the tile directly before riichi, -3 means three before.

Let's then look at the data for very early tile discards.

Well, they end up in furiten more often, but are pretty similar. Let's now look at the -1 numbers minus the -7 numbers to see the difference clearly. Positive numbers will be more dangerous when the tile is cut late, and negative numbers will be more dangerous when the tile is cut early.

Tile 1 before riichi minus Tile 7 before riichi

The ura suji of fives is safer when it's right before riichi. But, for the most part, there aren't big differences here.

Let's now look at the data for when the tile is cut after riichi.

Tile cut after riichi

This data looks quite normal. The 456 is always more dangerous than the 37 which is more dangerous than the 28 and so on. You can see the sujis being reduced clearly.

But, are the sujis more dangerous than early tiles or not? Let's make a table comparing those. We'll compare with the -7 tiles.

Tile 7 before Riichi minus After Riichi

They are very slightly more dangerous for the most part. Since -1 was more dangerous than -7, those will be slightly more dangerous. It's largely less than one percent different and we can blame the ryankans.

We can also look at the riichi tile itself.

Tile called riichi on

Now for some comparative tables. First, let's compare the riichi tile to the tiles cut after riichi.

Riichi Tile minus After Riichi

As is common knowledge, the suji of the riichi tile is more dangerous than usual. Riichis on 23 or 78 are also more commonly waiting on 19 or 28 tiles.

And now, for completeness, the last case:

Riichi Tile minus 7 before Riichi

Tiles near the riichi tile are more dangerous than tiles near the early discards, and tiles far away from the riichi tile are safer than tiles far away from the early discards. Makes sense. The influence of matagi suji and sakigiri.

So, this data says, if you have to choose, trust suji after riichi over suji before riichi.