Pros of discarding West Dora
1. It is likely to be safe now than later
2. It speeds up your hand (Important as Oya)
3. Might get Ittsu
4. Deters any player from getting any pair of this dora.
Cons of discarding West Dora
1. <Removed>
2. It slows down your hand
3. No chance of Ittsu
4. It will be painful when you drew the 2nd copy of West Dora
5. If West Dora is safe, other players with only 1 copy might discard it, this help to speed up their hand as well.
6. It will be a burden when you drew the 2nd copy of West Dora at the mid-game and the only copy of West Dora in the discard pool is the one you have discarded
7. There is a chance that toimen will ponned the dora this will put you in a disadvantage which means an increased chance of getting 3rd or last.
Examining the difference in speed
Discard west have 61 effective tiles shown below.
Discard 1sou have 51 effective tiles shown below.
We can see that discarding
is approx 20% faster than Reference: http://tenhou.net/2/?q=7m13356789s6789p3z
Examining the difference in value
We definitely need
and to complete ittsu. The below calculation is a very very rough estimation and has assumption that all live tiles are in the live wall. The chance of drawing is 1-0.75^3= 0.578 and the chance of drawing is 1-0.75^4 = 0.684 the same. To get both, it will be 0.578*0.684 = 0.395. The chance of drawing another West is 1-0.75^3 = 0.578.
From this, west is approx 45% higher in EV than ittsu.
This figure can be higher if we consider that after drawing the 2nd copy of west, the result will be shanpon machi. This means it is possible to get a 3rd copy of west to further increase in value. For the case of ittsu, once it is fixed, the value can not be further increased. We do not consider pinfu because both scenerio seem to have equal chance of pinfu. Ittsu might end up a kanchan machi which means no pinfu. Having a pair of west can still give pinfu depending on how the hand progress.
Examining the value of the extra 10 effective tiles
The 10 effective tiles are
Drawing
leads to riichi-nomi which worth 2k. will lead to ittsu but this has been covered above. So by discarding dora west, we are getting the extra 20% speed for a 2k hand + the chance of ittsu.
Discussion of point 4 of the pros and point 5+6 of the cons
While it is good that discarding dora now (if is passed) might lead to people discarding it subsequently. This means everybody's hand value will decrease. As Oya, this is an advantage. However with aka-dora unseen, it is possible that their hand value can be the same as ours. (I'm not sure if this is aka-nashi or aka-ri). Its more disadvantageous to discard a dora in aka-nashi but that's a different discussion altogether.
Furthermore, it is possible that for some of their hands, they might have space to keep the west dora in their hand. They have the choice to choose to discard it or keep. There is indeed an incentive to keep because if nobody call the 1st copy, it means that the remaining copies may be in the wall. Upon seeing the 1st dora being safe, opponents will have a choice now. If the dora is not delaying their hand, they will keep. If so, they can happily discard it. They also have the choice to aim for dora tanki as they know Oya is not about use it. Giving them our opponents more choices is definitely not a good thing
So it may not deter players from forming a dora pair as effectively as it might appear. It depends on the opponents' playing style.
Point 7
The chance is not high but if it happens, its really bad because:
i) Leaving toimen alone means he can tsumo mangan and put you to 3rd.
ii) If you run out of safe tiles, you might deal into his mangan and you will be last.
iii) You will be 2nd if he wins the hand.
iv) It is difficult to tell when he reach tenpai.
What kind of player are you?
Speed is generally more important as Oya. In consideration of the risks, are you willing to forsake or fight for the 20% speed of 2k hand + chance of ittsu? As analysed above, the EV of west is higher but speed is arguably more important to Oya and Oya's riichi is definitely scary. It really depends on the kind of player you are.
I'm a player who approach with caution. I made it a point that if I were to discard a dora, I must have either good hand shape or 1shanten. This hand has a very high uncertainty level, in the sense, this hand can worsen with getting kanchan around
and and riichi nomi on kan or shanpon middle tiles. If the chance of getting worsened hand shape is not low, it is equally good to work towards tanki dora West . My personal rule of thumb is also, trying not to make progress of my hand towards situations that have high uncertainty level because it means that I will have to look how the development goes before i can decide my next course of action. I dislike doing so, so my plan for my hand tend to starts from 1st row of discard. It kind of make my play more stable or consistent and less prone to mistakes. Personally, I do not mind giving up this hand if the development of this hand has no SSK or pinfu. In other words, I do not mind giving up getting 2k and fold. I would chase after 2k hand if the hand shape has confirmed to be good because it means high chance of tsumo. That's not 2k anymore. I'm the kind of player who, rather die with the dora, than to let people speed up their hand with ease. If the dora appear in somebody's hand only at mid 2nd row, that player will be slowed down. If he pushed with it to riichi, if means you have a safe tile.
At the end of the day, I do not dare to choose full-force offense with this hand at this stage. Hence I will still choose to discard
after much discussion and considerations.
