In oTree, a session is an event during which multiple participants take part in a series of tasks or games. An example of a session would be:
“A number of participants will come to the lab and play a public goods game, followed by a questionnaire. Participants get paid EUR 10.00 for showing up, plus their earnings from the games.”
A session is a series of subsessions; subsessions are the “sections” or “modules” that constitute a session. For example, if a session consists of a public goods game followed by a questionnaire, the public goods game would be subsession 1, and the questionnaire would be subsession 2. In turn, each subsession is a sequence of pages. For example, if you had a 4-page public goods game followed by a 2-page questionnaire:
If a game is repeated for multiple rounds, each round is a subsession.
Each subsession can be further divided into groups of players; for example, you could have a subsession with 30 players, divided into 15 groups of 2 players each. (Note: groups can be shuffled between subsessions.)
oTree’s entities can be arranged into the following hierarchy:
Session Subsession Group Player
- A session is a series of subsessions
- A subsession contains multiple groups
- A group contains multiple players
- Each player proceeds through multiple pages
You can access any higher-up object from a lower object:
In oTree, the terms “player” and “participant” have distinct meanings. The relationship between participant and player is the same as the relationship between session and subsession:
A player is an instance of a participant in one particular subsession. A player is like a temporary “role” played by a participant. A participant can be player 2 in the first subsession, player 1 in the next subsession, etc.