It can hardly be said often enough that a well controlled experiment, especially if conducted in the field, is worth more than a thousand observations.
As mentioned in Chapter 4, there are, in principle, two ways to observe the world. One is to observe without attempting to influence: standing back, watching and waiting for something interesting to happen. The other way is to experiment: actively interfering with the world to create an interesting response. The word experiment comes from the latin experior, which means to try or test. In this chapter we are going to look at how experimenters answer research questions by interfering with the world.