Sample Size Controls and the Scientific Method Science

Sample Size, Controls, and the Scientific Method Science is not just a guessing game!

Whether a scientist is seeking a cure for cancer or finding away to clean up oil spills, they all follow a set of steps that lead them through their research. These steps are necessary to ensure that scientists are conducting research in an accurate way. These steps are called the Scientific Method

The Scientific Method ©A series of steps that scientist follow in order to answer a question.

What do these words mean? Discuss the meaning of these words with someone at your table ©Observation ©Hypothesis ©Data ©Analyze

To test a hypothesis, we use a controlled experiment. ©A controlled experiment tests only one variable at a time. ©Discuss: What does “variable” mean?

Variables in an Experiment © The independent variable is changed or controlled by the scientist. It always goes on the Y –axis of a graph. © The dependant variable is responds to the change. It is what you are measuring. It goes on the Xaxis of a graph.

Can you identify the dependant and independent variables? ©How does salt affect water’s freezing point? ©Which fertilizer grows the largest apples? ©What size parachute slows a fall faster?

Controls in an Experiment © Good experiments have a control group. © Controls are NOT changed in any way, and are used to compare. They are the “standard”. © Example: You want to find a new recipe for better chocolate chip cookies. You could experiment with new recipes, comparing them to you Grandma’s famous recipe. Your Grandma’s famous recipe is your control!

Think about this…. You want to see how water affects plant growth. In your experiment, the amount of water and the size of the plant pots are both changed. What is wrong here? Why shouldn’t you change more than one variable at a time?

Sample Size Why do you need a large and random sample size? Imagine that you wanted to describe the size of the average rat, but this was the only one who volunteered! Does this rat represent all rats? ©Sample size is the number of measurements or subject in your experiment. ©Sample size should be large and random!

Discuss this question at your table…. © Mrs. D. conducted an experiment to see what kind of music helps student to learn. She used five of her favorite 8 th grade students for the experiment. She did the experiment one time, then reported to Mrs. Adkins that the school should play opera music over the intercom to help all students learn. What 3 mistakes did Mrs. D. make in her experiment ?