Survival Game

Code written by Scott Claessens. Email: scott.claessens@hotmail.co.uk

Please contact me if there are any issues.

Summary

The Survival Game is an open-source experimental economic game, run on oTree. The game simulates the life of a Maasai pastoralist herder. In a live interaction, pairs of individuals manage herds of cattle. Their herds grow over time, but are also subject to unpredictable disasters, potentially reducing their herd size below a minimum ‘survival threshold’. Individuals must request help from their partner to survive.

Click here to play a demo version of the Survival Game.

How to run the game

1. Download this repository to your computer.

2. Install oTree.

• Visit http://otree.readthedocs.io/en/latest/install.html to learn how to install oTree. You may also need to install a recent version of Python. IMPORTANT NOTE: This game will not work in oTree 2.0 or above.

3. Run oTree in your computer's command line.

• Use cd in the command line to set the working directory as the folder this README.md is saved in.
• Run otree resetdb to reset the database.
• Run otree runserver to run a local server, on which you can demo the game locally.
• Access http://127.0.0.1:8000/demo/ to demo the game locally when the server is running.

4. To run an actual experiment, you will need to push the game online, rather than using the local server.

• The oTree docs give all the information on how to use Heroku (or other platforms) to push games online and run experiments.
• Be sure to cite oTree if you use this game to collect data! Citation: Chen, D.L., Schonger, M., Wickens, C., 2016. oTree - An open-source platform for laboratory, online and field experiments. Journal of Behavioral and Experimental Finance, vol 9: 88-97.

Game schedule

1. Herd births and deaths. Each player's herd grows by a percentage, sampled from the Gaussian distribution specified by the parameters from session configs. Then, each player receives a shock ("disaster"), with a certain probability. The probability of shocks, the likelihood that they are correlated between ALL players, and the size (percentage reduction) of the shocks are all specified in the session configs.

2. Request. If there are other alive players to request from, players can request cattle from another player. Players must specify exactly how many cattle they want to request. If there is more than one other alive player, they must also specify exactly who they want to request from.

3. Fulfill requests. Players may fulfill the requests of others if they want. They are told how much a specific player is requesting, and can then give that player more / less than the requested amount, or nothing.

4. End of year. If there were cattle transfers, all players are informed of them. Then, the years ends. Final herd sizes are calculated, and if this falls beneath the minimum herd size threshold (specified in session configs), players are warned that they must increase it over the threshold or they run the risk of dying and being removed from the game. The amount of years, in a row, players can go with their herd under the minimum threshold is specified in the session configs.

Game parameters (session configs)

The following game parameters can be edited before beginning an oTree session (default values used for demos).

NOTE: Default parameters are loosely based on the original model of need-based transfers,
Aktipis, C. A., Cronk, L., & de Aguiar, R. (2011). Risk-pooling and herd survival: an agent-
based model of a Maasai gift-giving system. Human Ecology, 39(2), 131-140. Locally-run demo 
versions of the game will automatically use default parameters.

NOTE2: 'Number of players per group' & 'number of rounds' are hard-coded "constants" in oTree, 
and so they cannot be edited as simply as the parameters below. In this demo, they are set to 2 
and 10, respectively. To edit them, you will need to edit the code for the game directly:

   1. Go to SurvivalGame -> models.py
      - Edit "players_per_group" in Constants class
      - Edit "num_rounds" in Constants class
   2. Go to settings.py
      - Edit "num_demo_participants"
   3. You will need to then reset the database before playing the game: "otree resetdb"

Parameter	Default (Range)	Description
initialherd	70	The number of cattle that players start the first year with.
minherd	64	The minimum threshold for herd size. If a player's herd size goes BELOW this amount (equal is okay), they receive a warning and are told to increase it over the threshold. If they remain under the threshold for a certain number of years, they "die" and are removed from the game (see years_before_death).
growth_rate_mean	0.034	The mean of the Gaussian distribution from which growth rate is drawn.
growth_rate_sd	0.0253	The standard deviation of the Gaussian distribution from which growth rate is drawn.
shock_rate	0.2 (0-1)	The probability that a shock will occur on a given year. 0 = shocks do not occur. 1 = shocks occur every year.
shock_size_mean	0.15	The mean of the Gaussian distribution from which shock size is drawn.
shock_size_sd	0.05	The standard deviation of the Gaussian distribution from which shock size is drawn.
shock_correlated	0 (0-1)	The probability that, if a shock occurs, it will affect all individuals identically (i.e. the same value is drawn from the Gaussian distribution for everyone). 0 = shocks are not correlated. 1 = shocks are correlated between all individuals (i.e. when a shock occurs, it affects all players identically).
shock_predictable	False (boolean)	If this is True, shocks cease to occur probabilistically, ind instead occur predictably, every x years (see shock_predictable_years). Setting this to True bypasses both shock_rate and shock_correlated, and instead determines the occurence of a shock by counting the number of years since the player's last one.
shock_predictable_years	4	This value is only important if shock_predictable is True. It states how often shocks occur (in years). Shock size is still calculated independently for each player, and shocks need not affect players simultaneously (i.e. the beginning of the 4-year cycle is random for each player).
years_before_death	3	How many years players can go (in a row) under the threshold before "dying" and being removed from the game. The first year a player ends a year under the threshold counts as the first year.
nonrandom_network_limited_degree	False (boolean)	Determines whether a constrained, limited network structure is imposed on groups. If this is set to False, players can request cattle from any other player (unless that player has died). If this is set to True, players can only interact with a limited number of neighbours (determined by nonrandom_network_k_degree). This feature may be useful for very large groups.
nonrandom_network_k_degree	4	This value is only important if nonrandom_network_limited_degree is set to True. This value determines how many neighbours are included in each player's local network. This number must be between the group size and 2, and even numbers should be used (odd numbers necessarily lead to some one-way connections).
observability	True (boolean)	Determines whether players see the herd sizes of other players (and whether they are below the minimum threshold) on each screen as they play.
charts	True (boolean)	Determines whether players see a chart, visually displaying their current herd size on each screen. NOTE: HighCharts can slow pages down, so this may be worth deactivating.
summary_box	False (boolean)	Determines whether players see a box summarising the requests during the year, on each screen.
real_world_currency_per_point	0.01	USD ($) per cattle, used to calculate bonus payment
participation_fee	1.00	Base participation payment, in USD ($)

Dependent variables

NOTE: These are calculated for each player after they complete the game. 
The values are saved in the final round data.

Dependent Variable	Description
rounds_survived	The number of rounds the player survived.
overall_total_amount_requested	The total number of cattle the player requested.
overall_total_amount_received	The total number of cattle the player received.
overall_total_amount_given	The total number of cattle the player gave to others.
overall_received_given_totaldiff	The difference between the total number of cattle the player gave to others, and the total number of cattle the player received from others. Negative number means the player gave more cattle than they received, across all rounds.
overall_mean_amount_requested	The mean number of cattle the player requested. Calculated by taking the overall_total_amount_requested and dividing by rounds_survived.
overall_mean_amount_received	The mean number of cattle the player received. Calculated by taking the overall_total_amount_received and dividing by rounds_survived.
overall_mean_amount_given	The mean number of cattle the player gave to others. Calculated by taking the overall_total_amount_given and dividing by rounds_survived.
overall_num_shocks	The total number of shocks experienced.
overall_num_requests_made	The total number of requests made.
overall_num_requests_when_under_threshold	The total number of requests that were made, specifically when the player's herd size was under the minimum threshold.
overall_num_requests_responded_to	The total number of others' requests the player responded to (i.e. the player gave at least 1 cattle).
overall_repetitive_giving	When one player gives another player some cattle, the receiver becomes in "debt" to the sender. Giving cattle back to the sender removes the debt, but pushes debt onto the original sender. If a player gives cattle to a player who is already in debt to them, this count of overall_repetitive_giving increments by 1. This variable can be thought of as: the number of rounds in which the player sent cattle to someone who had not yet repaid a previous gift.
overall_repetitive_asking	If a player requests cattle from someone when they are already in debt to that person, this count of overall_repetitive_asking increments by 1. This variable could be thought of as: the number of rounds in which the player requested cattle from someone when they had not yet repaid a previous gift from them.