why is trade 3/4 of predicted?

[debeest]

In the attached game, there are demanded freights waiting to be delivered to Philadelphia (silk from Genoa) and to Hamburg (oil from Swaziland). In each case, I tried to calculate the expected delivery bonus according to the methods so thoroughly worked out by samson after extensive foundational work by William Keenan and others. In both cases, the delivery bonus is 3/4 of what I calculated (off by 4 in one case, a rounding error I'm sure). Have I done something wrong, or is there something wrong with the methodology?

Here are my calculations:

Swaziland base trade = 63
Hamburg base trade = 51
distance = 34 (Swaziland = 91,69; Hamburg = 73,29)

(63 + 51) x (34 + 10) / 48 = 104.5 = base value

Multipliers are continent (2), freight (3/2), commodity (3), post-railroad (2/3), post-flight (2/3), both with superhighways (2), and both with airports on different continents (2):

2 x 3/2 x 3 x 2/3 x 2/3 x 2 x 2 = 16

104 x 16 = 1664 = my predicted value
.75 x 1664 = 1248 (actual delivery value = 1252)

***********

Genoa base trade = 54
Philadelphia base trade = 42
distance = 29 (Genoa = 83,71; Philadelphia = 48,60)

(54 + 42) x (29 + 10) / 48 = 78

Multipliers are exactly as above, except the commodity bonus is 3.5, so the combined multiplier = 56/3 = 18.666.

78 x 56/3 = 1456 = my predicted value
.75 x 1456 = 1092 = actual delivery value


Since in both cases the actual value is 3/4 of the predicted value, I'm guessing that either the multiplier for airports or superhighways is wrong, or I've interpreted them wrong. Can anybody tell me?

[Old n Slow]

Isn't there a hit after Nav + Inv?, 2nd hit after RR?

[debeest]

Post-railroad (2/3) is listed in the multipliers I used. The hit after invention is a drop from 2 to 1, so I didn't mention it.

[solo]

Transportation modifiers are additive, so if you have superhighways and airports in both cities on different continents the total bonus is 200%, which means you multiply by 3 instead of by 4.

You can verify this by selling off the destination city's airport before delivering either freight. The amount earned from the delivery will only decrease by 1/3 and not by 1/2.

[debeest]

Thanks, Solo. Now I get it.

[Straybow]

Drop after RR is -33% and drop after AP is -33%, but relative to the unmodified total—net effect is -66%. That would be the equivalent of ×2/3 ×1/2 rather than ×2/3 ×2/3.

The end result is 3/9 rather than 4/9, which would also give the observed .75 factor.

Somewhere in there is a penalty for not delivering to a foreign civ… or is it a bonus for delivering to a foreign civ?