 Students now we are going to study the last experimental design in Kozai experimental designs which is natural experiment. In the study of a natural occurring situation as it is put in the real world, the researcher does not exert any influence over the situation but rather simply observes individuals and circumstances and comparing the current condition to some other condition. So in the natural experiment we do a natural phenomenon and on the basis of that natural phenomenon we see that before that natural phenomenon what was the human behavior and after that natural phenomenon what changed in the human behavior. Like an earthquake, a flood, a heavy rainy season or a natural event, a catastrophe then how people behaved after that event. So for this you do not design a pre-planned study and neither do you design a control group or a treatment group. When the event occurs after that we can see the behavior of people. Like recently last year in Pakistan severe floods came from the northern areas to the central Punjab and Sindh. So there were a lot of predictions and how people were adjusted and how they were impacted so that can be observed only after this event. So natural experiment are actually observational studies which can be taken to assess the outcomes and impacts of policy interventions. So these are purely observational studies in which pre-planned treatment is not given. In fact after the event what response came we can study it. Like I give an example of a study in the US in which day light was seen as a road accident that when you increase the time period of day light then how it reduced the road accidents. So it came to know that when there is day light then there are less road accidents as compared to when there is no day light.