Experiment!: Planning, Implementing and Interpreting

6.1 What is an Experiment?

To discuss experimental method we need a definition to set it apart from mere observation. Since the experimenter interferes with the world to obtain useful data, we could say that an experiment involves a strategic manipulation of a system to create an organized response, in order to answer a specific question. These three criteria are a good start, but are they sufficient? When putting some oranges on the scales at the fruit market to find out what we should pay for them, we are making a strategic manipulation of a system (the scales) to create an organized response (the readout), in order to answer a specific question (what should we pay). Most people would probably agree that this is no more an experiment than looking at the speedometer when driving your car. Setting up a system and obtaining information from it by passive observation is not experimentation. When Mr. Green counted his apples in Chapter 2 he was not experimenting. If he had tested different fertilizers to increase the yield of apples, he would have been conducting an experiment.

Exercise 6.1: Before reading further, take a minute to reflect on why the fertilizer test would be an experiment, and just counting the apples is not.

An experiment imposes a treatment on something. It exerts a stimulus on the system under study. As experimenters we are interested in the response to this stimulus, because we hope it will say something about how the system works. If we were interested ...