Judging Experiments and Designs

By the end of this lesson, you will be able to look at someone's experiment or invention and decide how well it was planned and what could make it better.

Scientists and engineers do not just build things and hope for the best. They evaluate their work, which means they judge how well a design or an experiment met its goal, using evidence instead of opinions. A good experimental design tests one thing at a time and collects enough data to trust the results. A good engineering design solves a real problem while staying inside its constraints, which are the limits on things like cost, size, time, or materials.

Imagine a class in Houston building a shade structure for a school bench so students stay cooler at lunch. One group covers the bench with black plastic. It blocks sunlight, but the black material soaks up heat, so the bench feels hotter. Another group uses a white canvas cover and measures the temperature under it every day at noon for a week. Their data show the bench stays about eight degrees cooler than the uncovered bench. You can evaluate both designs by asking which one actually met the goal, which one was tested with repeated measurements, and which one stayed under the twenty dollar budget.

When you evaluate an experiment, ask whether the variable, the one factor that is purposely changed, was the only thing different between the tests. If the second group had also moved the bench under a tree, you could not tell whether the canvas or the tree caused the cooling. Ask, too, whether the test was repeated, whether the measurements were taken the same way each time, and whether the data really support the conclusion.

Try it: If a student tests a new paper airplane design but throws it only one time, on one windy day, what is the biggest weakness in that design test?