• You are researching the effect of music-listening on studying efficiency
• You might divide your subjects into two groups: one would listen to music and the other (control group) wouldn’t listen anything!
• You give them a test
• Then, you compare grades between the two groups

Differences between observational and experimental data:
– Observational data: measures the characteristics of a population by studying individuals in a sample, but doesn’t attempt to manipulate or influence the variables of interest
– Experimental data: applies a treatment to individuals and attempts to isolate the effects of the treatment on a response variable
Observational data: find 100 women age 30 of which 50 have been smoking a pack a day for 10 years while the other have been smoke free for 10 years. Measure lung capacity for each of the 100 women. Analyze, interpret and draw conclusions from data.
Experimental data: find 100 women age 20 who don’t currently smoke. Randomly assign 50 of the 100 women to the smoking treatment and the other 50 to the no smoking treatment. Those in the smoking group smoke a pack a day for 10 years while those in the control group remain smoke free for 10 years. Measure lung capacity for each of the 100 women.
Analyze, interpret and draw conclusions from data.
Source

We do studies to gather information and draw conclusions. The type of conclusion we draw depends on the study method used:

• In an observational study, we measure or survey members of a sample without trying to affect them.
• In a controlled experiment, we randomly assign people or things to groups. One group receives a treatment and the other group does not.

Source: Khan Academy