research is located in a continuous spectrum between the "pure" lab experiments and natural experiments. It is conducted in a diversified environment with various types of subjects. The following four types of research experiments are distinguished according to the type of research problem they solve. Specific populations The hypothesis may have to be tested by using specific populations. Or the researcher hopes to test if a result could be generalized to a broader or a representative, population. Measurement Lab procedures can be put into use in the measurement of the field. Risk aversion, time preference (patience), altruism, cooperation, competition, and in-group discrimination are the most common measures. Recruiting the treated This kind of lab-in-the-field experiment is for the circumstance that participants who have already been treated are being recruited. The experimenters are recruiting rather than implementing treatments. Teaching The purpose of the experimenter may be to teach the target population about the games by using a lab-in-the-field approach. Through this process, the experimenter could target a particular policy problem. The game could be the treatment in this circumstance. Audit study Audit studies are often used for measuring bias or discrimination. Audit studies are part of the constructure of a giant field experiment. This field experiment aims to measure the behaviour of participants in the field rather than to change it. In most cases, researchers use the ways like sending messages to measure participants' behaviours unobtrusively. Ethics Experimental research methods in political science have unavoidable ethical questions: Can humans be used for experiments? While experiments in political science usually do not cause physical harm, the elements of deception is commonly existing. When conducting political science experiments, researchers must intervene in the process of data generation. Political science, as social science, studies human behaviour. Then political science experiments will inevitably have an impact on people. For example, subjects in experiments make choices they would not otherwise face, or subjects are put into experiences or controls that they would not otherwise have. The experimental process itself is not the only way political science research activities affect human life. Other influences include the influence of the dissemination of experimental results, the influence of political science scholars on their students, and the influence of research results on institutions and professional organizations. Just like the ethics of most other professions, political scientists have ethics. In 1967, a committee was created by the American Political Science Association