An Introduction to Z-Tree In a computerized experiment, an experimentor and a number of subjects need to communicate with one another. Z-Tree (Zurich Toolbox for Readymade Economic Experiments) designed by Urs Fischbacher is an easy to learn programming language for experiments. A researcher writes the code in Z-Tree, and subjects will connect to the program via Z-Leaf. Software Tutorial and Reference Manual available at

Z-Tree Software Z-Tree allows researchers to easily develop and to carry out economic experiments. It includes features that are needed in most experiments:  communication between the computers;  data saving;  display time;  calculate profit;  flexible screen layout. Fischbacher maintains a friendly user-discussion group.

How does it work? Ztree.exe Experimentor PC Auction.ztt Subject PCs Zleaf.exe Instructions, Parameters, results, Subject’s inputs Hard drive or server Experimental data

Z-Tree Starts with one untitled treatment

Some Terms An experiment consists of sessions; Each session can have one or more treatments; Each treatment may last one or more periods; In each period, the subject may go through one or more stages. In each stage, the experiment needs to specify what the subjects should know and tell them what decisions they should make.

A Simple Public Good Experiment Suppose we have 24 subjects, participating in a single treatment session. Subjects are put in 4-person groups; and will play 10 periods of public good contribution game. The number of subjects, number of groups, # of playing periods as well as show up fee, etc. can be specified right before the experiment starts in the general parameters.

Public Good Experiment Each subject will be given an endownment of 20 ECU (Experimental Currency Units); They will be asked to decide how many ECUs they would like to contribute to the public good; Total contributions to the public good will have be multiplied by an efficiency factor, which will then be equally divided by the subjects in the same group; Money uncontributed to the public good have a return of 1 and is privately owned.

Public Good Experiment Suppose that we would like to have two treatments in one session: Treatment 1: EfficiencyFactor = 1.6; Treatment 2: EfficiencyFactor = 2.4.