Comparing Results of an Investigation with Predictions

Instructor: Amanda Robb
In this lesson, we'll be learning how to compare the results of experiments to what we predicted would happen. We'll learn how to look for validity and go through the scientific method to revise your experiment.

Starting a Scientific Investigation

You've probably conducted some of your own experiments in science class at school. What were the first steps before you started working with the materials? You probably did some reading or got information from your teacher about the topic. This step is called background research, so you can understand what's already been studied about a topic.

Based on the background research, you need to come up with a question you want to answer about the topic. Using your new knowledge, you propose a hypothesis, or an educated guess about what you expect to see based on what you've learned. Usually your hypothesis takes the form of an ''if - then - because'' statement. If we do something, then something will happen because of a scientific phenomenon.

Let's use the following example for this lesson. In science class, you want to know how sunlight affects plant growth. You have two plants. You keep one in the dark and one in the light and record their growth over a period of 5 days.

Before we talk about what to do with your results, create a hypothesis of your own. It might be something like this: If we keep one plant in the dark and one plant in sunlight, then the plant in the dark will not grow because it needs sunlight to do photosynthesis to make food.

Analyzing Your Results

After you create your hypothesis you need to test it. You carry out the planned experiment and collect the data. But what do you do once you have your results? Your teacher might ask you to compare your results to your predictions. But what does that really mean, and what are you supposed to write?

Let's say your plant in the sunlight grew 4 inches and the plant in the dark did not grow at all. To compare these results to your prediction, the first step is to go back to your hypothesis.

Re-read your hypothesis you wrote in the beginning to refresh your memory. In your hypothesis, you said that the plant in the dark would not grow. Now, go back to your data. How much did the plant in the dark grow? It grew zero inches. This agrees with your hypothesis, so your hypothesis was supported and your predictions matched your results. You can infer that your reasoning was correct since your data and predictions were in agreement. In your assessment, it's important to refer to your data and give exact numbers. Remember to always give evidence to support your claim!

However, if you only did the experiment once, it's possible the results were due to chance. The only way to confirm that your results were valid, or true, is to repeat the experiment multiple times. Usually, scientists repeat an experiment three times, but the more times you do an experiment and get the same results, the more valid the results are.

Dealing with Conflicting Results

In this example, our results matched our prediction perfectly. But in reality, science is messy and results don't always match our predictions. What do you do if your results are different than what you predicted?

Let's say in our example the plant in the dark grew one inch. Does this result match your hypothesis? No, it does not. That doesn't mean your experiment was bad, though! All data is good data, even if it isn't what we expected.

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