2.1 A lab experiment

Let’s consider a simple example. Suppose you want to investigate the importance of sunlight for the growth of a jade plant. How might you proceed?

You might start by obtaining two baby jade plants from the same seller. Place jade plant A near the window sill, where it can receive ample sunlight, and place jade plant B in a closet within the same room, where it receives no sunlight. To ensure fairness, keep the room temperature uniform and water both plants equally, once a week. After some time, you evaluate the growth of both plants.

Of course, this is just a thought experiment—you wouldn’t actually do this because we already know the plant in the closet would not survive. However, this example illustrates the core idea of a controlled experiment.

What’s happening in our thought experiment? We’ve essentially conducted a minimal lab experiment:

1. Treatment Assignment: The “treatment,” or variable of interest, is the exposure to sunlight. You control which plant receives the treatment and which does not.

2. Controlling for Other Variables: Factors like water and temperature, which could also influence plant growth, have been held constant.

3. Measurement: You can (more or less) accurately measure the growth of the plant (e.g., height). Eventually, you can measure which one survived.