Another method of observation with intervention is field experiment. What is a field experiment? When an observer controls one or more conditions in a natural setting in order to determine the effect on behaviour, this procedure is called field experiment. The field experiment represents the most extreme form of intervention in observational methods. The essential difference between field experiments and other observational methods is that researchers have more control in field experiments. Now let's take a look at observation without intervention. Observation without intervention is also called naturalistic observation because its main purpose is to describe behaviour as it normally occurs, that is, in a natural setting, without any attempt by the observer to intervene. An observer using this method of observation acts as a passive recorder of what occurs. The events occur naturally and are not controlled by the observer. OK, in today's lecture,we have focused on how to make decisions of sampling before beginning our observation, and what we can do during observation. I hope what we've discussed will help you in your future research design.