I don't know about you but I love to know how I'm doing compared to my peers  be it salary, vacations, cars or my skill at Diplomacy.
As such I enjoy the YARS and JDPR scales provided by the Dip Pouch. I want to express great thanks to those involved in keeping these things running.
The YARS system is fine but does favor the prolific player. JDPR should be more fair? However, when I first looked at the JDPR, I was scared by the math. I firmly decided to sit back, let Doug Massey do the calculations and see what happens to my score each month. As my results improved I became keen to see where my score was going to go to and so I delved a little into the JDPR mechanics. But still, I thought, why mess with it?
But now I find myself in a different position. I'm playing a game which is settling into a 4 way draw. The question is whether to set draw or try and break out of the deadlock. The risk with attacking is that the position in the game is thus that it almost ensures one's elimination for doing this. Diplomatically it's difficult as it's broadcast only press. But what will the 4 way do to my JDPR? Perhaps I shouldn't base my decision in the game on my JDPR rating but it does come into it. After all I'm obsessed with comparisons, as I said.
So I got to thinking that I can't be the only player who would like a user's guide to the JDPR.
My attempt is to simplify the JDPR by making some assumptions that allow a user to quickly glean some basic information  to broad brush the change to his/her JDPR based on simple scenarios.
So here goes. You can find a complete break down of the math of the system on the DipPouch email section. Mine is a much simplified version.
The big assumption  This is standard diplomacy  no variants and you've played from the start of the game. All of my calculations are to one decimal place. Not accurate but as I said I want to broadbrush the impact.
JDPR relies on calculating your expected score from a game and comparing it to your actual score and multiplying by a factor to weight the quality of the game.
Hence:
Where E and V reflect the quality of the game and S is your actual score and X is your expected score.
First we need to know your score from the game in progress... Dead easy.
# of players in draw  Score S 

1 ie solo victory 
7.0 
2 
3.5 
3 
2.3 
4 
1.8 
5 
1.4 
6 
1.2 
7 
1.0 
loss 
0 
Now your expected score. A little more complicated but using this simple table an approximation may be gleaned quite quickly.


Your JDPR  



800 
900 
1000 
1100 
1200 
1300 
1400 
1500 
1600 
1700 
1800 
1900 
2000 

Their 
800 
1.0 
1.2 
1.4 
1.6 
1.9 
2.2 
2.5 
2.8 
3.2 
3.5 
3.9 
4.2 
4.5 

900 
0.8 
1.0 
1.2 
1.4 
1.6 
1.9 
2.2 
2.5 
2.8 
3.2 
3.5 
3.9 
4.2 

1000 
0.7 
0.8 
1.0 
1.2 
1.4 
1.6 
1.9 
2.2 
2.5 
2.8 
3.2 
3.5 
3.9 

1100 
0.6 
0.7 
0.8 
1.0 
1.2 
1.4 
1.6 
1.9 
2.2 
2.5 
2.8 
3.2 
3.5 

1200 
0.5 
0.6 
0.7 
0.8 
1.0 
1.2 
1.4 
1.6 
1.9 
2.2 
2.5 
2.8 
3.2 

1300 
0.4 
0.5 
0.6 
0.7 
0.8 
1.0 
1.2 
1.4 
1.6 
1.9 
2.2 
2.5 
2.8 

1400 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
1.0 
1.2 
1.4 
1.6 
1.9 
2.2 
2.5 

1500 
0.3 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
1.0 
1.2 
1.4 
1.6 
1.9 
2.2 

1600 
0.2 
0.3 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
1.0 
1.2 
1.4 
1.6 
1.9 

1700 
0.2 
0.2 
0.3 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
1.0 
1.2 
1.4 
1.6 

1800 
0.2 
0.2 
0.2 
0.3 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
1.0 
1.2 
1.4 

1900 
0.1 
0.2 
0.2 
0.2 
0.3 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
1.0 
1.2 

2000 
0.1 
0.1 
0.2 
0.2 
0.2 
0.3 
0.3 
0.4 
0.5 
0.6 
0.7 
0.8 
1.0 
The technique is to know your own JDPR (top row) and calculate or estimate your opponent's JDPR. Now most games are gunboat and so you simply don't know their JDPR. But you can make a decent guess from their press, is this a newbie game or for players with high JDPR rankings etc. Read X off from the appropriate cell in the table.
Now we calculate SX.
So here's an example. Let's assume my JDPR is 1200 and I estimate my opponents to have a JDPR average of 1100 (above average but not really high). So my expected score is 1.2 (X=1.2).
A 6 way draw will see my JDPR remain static 1.21.2=0. Anything better than this will boost my JDPR and anything less will reduce it.
Now imagine if you will that I have a run of great results and I knock Jorge Llambias off the top JDPR ranking as my ranking grows to 2000 (my dream!). I now play a game with the same 6 players who have an average JDPR of 1100 (still above average). My expected JDPR score now has grown to X=3.5. Hence a 2 way draw will keep my JDPR up at 2000 and anything less will reduce my ranking. The JDPR system expects a great deal of the top players if they expect to stay on top.
In my particular situation that prompted this work, I'm unsure of my own JDPR as I've completed several games since the last JDPR ranking was done. So let's assume my ranking is 1400. The game is of good quality so I think I'm playing decent players. I'll guess they have a JDPR average of 1200. Hence my particular X=1.4. A 4 way gives me a S=1.8. SX=0.4 so my score would increase by getting the 4 way draw.
If I'm wrong though and my JDPR is actually increased to 1500 and my opponents only have an average JDPR of 1000 then SX=1.82.2= 0.4. My JDPR would go down.
I find this quite a useful tool to see what's needed to boost my score.
This alone is enough to glean an idea as to what will happen to your JDPR but to put some scale on it we need to look at the Value of the game.
In the standard game two things affect the value of the game  press and the number of rated players.
Press may be partial, broadcast or no press. Partial is believed to be the most severe indicator of ability and so these are weighted 1.0,0.8 and 0.5 respectively.
To be rated, players must have 7 games that are valid for JDPR scoring. The theory is to weight games more heavily that include experienced players. A newbie game will have less JDPR impact than a game full of experienced players.Combining these two variables in the following table will show the value of the game.
# of rated players  Partial  Broadcast  None 

0  7.5  6.0  3.8 
1  8.6  6.9  4.3 
2  9.6  7.7  4.8 
3  10.7  8.6  5.4 
4  11.8  9.4  5.9 
5  12.9  10.3  6.4 
6  13.9  11.1  7.0 
7  15.0  12.0  7.5 
In my particular example, the game is gunboat so I'm unsure as to how many players are rated but it's a quality game so I'm going to assume that 7 (all of us) are rated. It is broadcast only so my Value is 12.0
Just one thing left to know...experience.
The theory is that as a new player you want your JDPR to change rapidly to truly reflect your actual ability whilst once you're more experienced, a single bad game shouldn't be the end of the world for your JDPR rating. An exponential math has been worked out to allow this but basically, the following table allows an approximation as to your experience value to be made. # of games is the number of games you have completed valid for JDPR ranking. Ie mercy positions don't count but all other losses and solos and draws do.
#games 
E 
0 
5.0 
10 
3.0 
20 
2.3 
30 
2.0 
50 
1.7 
100 
1.4 
200 
1.2 
For me I've completed close to 10 games so my E is 3.0
The final calculation. Delta is the change in my JDPR ranking.....
Delta = E * V * (SX)
Remember:
my E is 3
my V is 12
my SX was either 0.4 or 0.4 dependent upon my guesses as to JDPR ranking of myself and my opponents.
My JDPR will change by only 14 points based on these assumptions. That's a very small change whatever happens. Phew!
Of course were I to lose the game by pushing on for an elimination, my E and V would stay the same but S would become 0 whilst X remained at 1.4 or 2.2 dependent on my assumptions.
This would lose me 50 or 79 points respectively.
Being upbeat, a solo would give me an S of 7 which would yield 202 points or 173 dependent on my JDPR point assumptions.
As I said, I will not solely base my decision on this analysis but I will consider it as further evidence to help make my decision.
David Degville (fosrocdd@cs.com) 
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