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This study of hut outcomes was conducted on version 2.4.2, mostly on Deity/raging hordes at various map sizes. It used both reload testing and continous play testing. Both types of tests gave similar statistical results.
The study was done in two parts. The first part was concerned with determining what factors affect the frequency of the five types of outcome: Tribes, Gold, Mercenaries, Scrolls and Barbs. The second part studied the specific results available from each outcome type.
Much of the information reported here is already well known but some conclusions, hopefully, will be new and able to help resolve long standing disputes.
Rules governing the five types of outcomes
There are five possible outcomes from tipping a hut: Tribes (including nomads), Gold, Mercenaries, Scrolls, and Barbarians. The base chance of each of these outcomes is equal (20%), stated as a ratio this is: 1:1:1:1:1. However, certain game circumstances modify this ratio in predictable ways. These can be expressed in six rules.
No Cities Rule
When a hut is tipped by a Civ which has no existing cities and the Turn# is less than 50 (i.e. <1500BC on Diety), then both Tribes and Barbarians are suppressed and their chances are added to Mercenaries. Thus the outcome ratio becomes 0:1:3:1:0 in TGMSB order.
If the Turn# is greater than or equal to 50, then this rule does not apply and the ratio is normal, 1:1:1:1:1. Under these circumstances, it is possible to tip a hut for a Tribes outcome and, on suitable terrain, have it become your capital - complete with a Palace.
Near City Rule
If the distance from a hut to the nearest city is less than 4 (as measured by the rectangle system or the formula for distance given in "Calculating Caravan Delivery Payments") then both Tribes and Barbarians are suppressed and their chances are added to Mercenaries. The outcome ratio becomes 0:1:3:1:0 in TGMSB order.
Nomads Rule
If a Civ has more than one existing nomad (NONE settler) per 8 cities, the nomads-result of the Tribes outcome is suppressed and the chance is added to Scrolls.
With less than 8 cities a single NONE settler suppresses the nomad result. There must be at least 8 cities to support one existing nomad, 16 cities to support two, 24 cities to support three, etc. If not, then Nomads are suppressed and the outcome ratio on nomad-suited terrain becomes: 0:1:1:2:1.
Continent Rule
If a Human Civ tips a hut on a continent on which it has no existing cities (but does have cities elsewhere) and the distance from the hut to the nearest city is greater than 12, then the outcome ratio is: 7:2:2:2:2. In other words, there is a 47% chance of a Tribes outcome under these circumstances.
If the Civ is an AI, then the chance of a Tribes outcome is 100%.
Note, all rules are applied together. For example, under these circumstances if the terrain is nomad-suited and the nomad-result is being suppressed by the Nomads Rule, the Tribes chance is added to Scrolls and the outcome ratio becomes 0:2:2:9:2.
Invention Rule
Once a Civ acquires Invention, the Scrolls outcome is suppressed and its chance is added to Gold. The outcome ratio becomes 1:2:1:0:1 in TGMSB order.
Explosives Rule
After any Civ acquires Explosives, the Nomad result is suppressed and its chance is added to Gold. Thus, on Nomad-suited terrain, the outcome ratio becomes 0:2:1:1:1.
These are, I believe, the only factors affecting the type of outcome from huts. More specifically, the following factors were tested and found to have no statistical effect on hut outcomes:
- The direction of the tile from which the hut was tipped.
- The turn# on which the hut was tipped.
- The type of unit which tipped the hut.
- The terrain of the hut (other than the Tribes/Nomad terrain dependency.)
- The location or continent# of the hut.
Part Two - Results of outcome types
Tribes
The Tribes outcome has two possible results: Advanced Tribes and Nomads. Terrain is the determining factor in which is selected.. Advanced Tribes occur only on Grasslands or Plains. All other terrain types produce nomads. Nomads can also occur on Plains or Grasslands when the surrounding terrain makes the site poorly suited for a city.
The Nomads result is subject to the Nomads Rule and the Explosives Rule (see above).
Before 1000AD, all cities founded from Advanced Tribes have a size of 1. After that date, the size of the city can be 1 to 4. It will always have a Temple. In addition, it has a 50% chance of having a Marketplace, 33% chance of a Granary, and a 25% chance of a Library.
Gold
The Gold outcome has three results: 25 gold, 50 gold, or 100 gold. These occur in a ratio of 4:10:1 on Deity difficulty level. Lower difficulty levels increase the chance of 100 gold and decrease the chance of 25 gold. After the year 1000AD, each of these amounts are doubled.
Mercenaries
There are two result classes of the Mercenary outcome. In general, these can be described as 1-move units and 2-move units. Each of these result classes has an equal chance of appearing from a hut. The specific types of units depend on the discovery of technologies. Once the governing technology has been discovered by any Civ, the unit begins appearing from huts.
Initially, Horsemen and Chariots are available as 2-move units in a ratio of 2:1
Polytheism introduces Elephants. The ratio of Elephant, Horse, and Chariot is 3:2:1.
Chivalry replaces all 2-move units with Knights.
Monotheism replaces all earlier 2-move units with Crusaders.
Leadership replaces earlier 2-move units with Dragoons.
Conscription replaces all 2-move units with Riflemen, a 1-move unit.
Archers are the initial 1-move unit.
Iron Working causes Legions to replace Archers as the 1-move unit.
Gunpowder causes Musketeers to replace Legions as the 1-move unit.
Guerrila Warfare causes Fanatics to replace Musketeers as the 1-move unit.
Mercenary units are supported by the nearest city, unless the nearest city is foreign in which case they are NONE.
Scrolls
The result of a scroll outcome can be any unacquired Civilization Advance for which the Civ has all prerequisites.
The chance of obtaining a specific Advance can be calculated by listing the position numbers of possible advances in an alphabetically-ordered list of all advances (as under @Civilize in Rules.txt). An advance's chance of selection is statistically equal to the distance between its position and the position of the advance above it (wrapping the list from bottom to top).
For example, with no starting techs the list of possible advances and position numbers out of the total of 93 advances would be:
Alphabet 2
Bronze Working 9
Ceremonial Burial 10
Horseback Riding 37
Masonry 48
Pottery 66
Warrior Code 88
And the chances for each advance are:
Alphabet 7/93
Bronze Working 7/93
Ceremonial Burial 1/93
Horseback Riding 27/93
Masonry 11/93
Pottery 18/93
Warrior Code 22/93
Note that Ceremonial Burial, appearing immediately after Bronze Working, has only 1 chance in 93 while Horseback Riding benefits from the long gap between itself and CB.
Barbarians
(incomplete)
General Conclusion.
The assumption of randomness in the determination of hut outcomes appears to be valid. Although sequences of similar outcomes do occur, they are unpredictable and fall within bounds predicted by a random model modified by the rules and conditions described above.
The study was done in two parts. The first part was concerned with determining what factors affect the frequency of the five types of outcome: Tribes, Gold, Mercenaries, Scrolls and Barbs. The second part studied the specific results available from each outcome type.
Much of the information reported here is already well known but some conclusions, hopefully, will be new and able to help resolve long standing disputes.
Rules governing the five types of outcomes
There are five possible outcomes from tipping a hut: Tribes (including nomads), Gold, Mercenaries, Scrolls, and Barbarians. The base chance of each of these outcomes is equal (20%), stated as a ratio this is: 1:1:1:1:1. However, certain game circumstances modify this ratio in predictable ways. These can be expressed in six rules.
No Cities Rule
When a hut is tipped by a Civ which has no existing cities and the Turn# is less than 50 (i.e. <1500BC on Diety), then both Tribes and Barbarians are suppressed and their chances are added to Mercenaries. Thus the outcome ratio becomes 0:1:3:1:0 in TGMSB order.
If the Turn# is greater than or equal to 50, then this rule does not apply and the ratio is normal, 1:1:1:1:1. Under these circumstances, it is possible to tip a hut for a Tribes outcome and, on suitable terrain, have it become your capital - complete with a Palace.
Near City Rule
If the distance from a hut to the nearest city is less than 4 (as measured by the rectangle system or the formula for distance given in "Calculating Caravan Delivery Payments") then both Tribes and Barbarians are suppressed and their chances are added to Mercenaries. The outcome ratio becomes 0:1:3:1:0 in TGMSB order.
Nomads Rule
If a Civ has more than one existing nomad (NONE settler) per 8 cities, the nomads-result of the Tribes outcome is suppressed and the chance is added to Scrolls.
With less than 8 cities a single NONE settler suppresses the nomad result. There must be at least 8 cities to support one existing nomad, 16 cities to support two, 24 cities to support three, etc. If not, then Nomads are suppressed and the outcome ratio on nomad-suited terrain becomes: 0:1:1:2:1.
Continent Rule
If a Human Civ tips a hut on a continent on which it has no existing cities (but does have cities elsewhere) and the distance from the hut to the nearest city is greater than 12, then the outcome ratio is: 7:2:2:2:2. In other words, there is a 47% chance of a Tribes outcome under these circumstances.
If the Civ is an AI, then the chance of a Tribes outcome is 100%.
Note, all rules are applied together. For example, under these circumstances if the terrain is nomad-suited and the nomad-result is being suppressed by the Nomads Rule, the Tribes chance is added to Scrolls and the outcome ratio becomes 0:2:2:9:2.
Invention Rule
Once a Civ acquires Invention, the Scrolls outcome is suppressed and its chance is added to Gold. The outcome ratio becomes 1:2:1:0:1 in TGMSB order.
Explosives Rule
After any Civ acquires Explosives, the Nomad result is suppressed and its chance is added to Gold. Thus, on Nomad-suited terrain, the outcome ratio becomes 0:2:1:1:1.
These are, I believe, the only factors affecting the type of outcome from huts. More specifically, the following factors were tested and found to have no statistical effect on hut outcomes:
- The direction of the tile from which the hut was tipped.
- The turn# on which the hut was tipped.
- The type of unit which tipped the hut.
- The terrain of the hut (other than the Tribes/Nomad terrain dependency.)
- The location or continent# of the hut.
Part Two - Results of outcome types
Tribes
The Tribes outcome has two possible results: Advanced Tribes and Nomads. Terrain is the determining factor in which is selected.. Advanced Tribes occur only on Grasslands or Plains. All other terrain types produce nomads. Nomads can also occur on Plains or Grasslands when the surrounding terrain makes the site poorly suited for a city.
The Nomads result is subject to the Nomads Rule and the Explosives Rule (see above).
Before 1000AD, all cities founded from Advanced Tribes have a size of 1. After that date, the size of the city can be 1 to 4. It will always have a Temple. In addition, it has a 50% chance of having a Marketplace, 33% chance of a Granary, and a 25% chance of a Library.
Gold
The Gold outcome has three results: 25 gold, 50 gold, or 100 gold. These occur in a ratio of 4:10:1 on Deity difficulty level. Lower difficulty levels increase the chance of 100 gold and decrease the chance of 25 gold. After the year 1000AD, each of these amounts are doubled.
Mercenaries
There are two result classes of the Mercenary outcome. In general, these can be described as 1-move units and 2-move units. Each of these result classes has an equal chance of appearing from a hut. The specific types of units depend on the discovery of technologies. Once the governing technology has been discovered by any Civ, the unit begins appearing from huts.
Initially, Horsemen and Chariots are available as 2-move units in a ratio of 2:1
Polytheism introduces Elephants. The ratio of Elephant, Horse, and Chariot is 3:2:1.
Chivalry replaces all 2-move units with Knights.
Monotheism replaces all earlier 2-move units with Crusaders.
Leadership replaces earlier 2-move units with Dragoons.
Conscription replaces all 2-move units with Riflemen, a 1-move unit.
Archers are the initial 1-move unit.
Iron Working causes Legions to replace Archers as the 1-move unit.
Gunpowder causes Musketeers to replace Legions as the 1-move unit.
Guerrila Warfare causes Fanatics to replace Musketeers as the 1-move unit.
Mercenary units are supported by the nearest city, unless the nearest city is foreign in which case they are NONE.
Scrolls
The result of a scroll outcome can be any unacquired Civilization Advance for which the Civ has all prerequisites.
The chance of obtaining a specific Advance can be calculated by listing the position numbers of possible advances in an alphabetically-ordered list of all advances (as under @Civilize in Rules.txt). An advance's chance of selection is statistically equal to the distance between its position and the position of the advance above it (wrapping the list from bottom to top).
For example, with no starting techs the list of possible advances and position numbers out of the total of 93 advances would be:
Alphabet 2
Bronze Working 9
Ceremonial Burial 10
Horseback Riding 37
Masonry 48
Pottery 66
Warrior Code 88
And the chances for each advance are:
Alphabet 7/93
Bronze Working 7/93
Ceremonial Burial 1/93
Horseback Riding 27/93
Masonry 11/93
Pottery 18/93
Warrior Code 22/93
Note that Ceremonial Burial, appearing immediately after Bronze Working, has only 1 chance in 93 while Horseback Riding benefits from the long gap between itself and CB.
Barbarians
(incomplete)
General Conclusion.
The assumption of randomness in the determination of hut outcomes appears to be valid. Although sequences of similar outcomes do occur, they are unpredictable and fall within bounds predicted by a random model modified by the rules and conditions described above.
I am sorry, I have read your post too fast. My results are exact to yours. 
Also I didn't realize that the barb-free area is defined by the distance from the city. 
Never in a million years would I have thought of that.
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