Experimental Design

Every experiment in SCIENCE contains several Key components or parts. This format is standard throughout the world and is required for a valid experiment. A valid experiment is one that is repeatable by other scientists. Anyone who repeats the same experiment should get the same results as the original scientist.

First, All experiments need a title First, All experiments need a title. The title should reflect the nature of the experiment. For example, if your experiment involves taking frogs and exposing them to tobacco smoke to see what it does to their lung capacity, A title would be: The effect of tobacco smoke on frog lung capacity.

Second, experiment needs a dependent and independent variable The dependent variable is what we are trying to test or find out. It is usually the thing we are measuring. In our example above, the dependent variable is the amount of air that the frog’s lungs can hold

The independent variable is the part of the experiment that we are manipulating to see what will happen. In our example above we are manipulating the amount of tobacco smoke that the frogs are exposed to.

A valid experiment will have only have one dependent and independent variable. If there are more than that, the scientists can not be sure what actually caused the results to occur like they did.

Thirdly, each experiment needs a hypothesis Thirdly, each experiment needs a hypothesis. Most hypothesis follows an if…then… format. The hypothesis is just an educated guess as to what will occur in the experiment. Educated guess means that you are basing your guess on what you have learned in the past, on your previous knowledge. Some hypothesis even require you to state why you made that prediction

Lastly, every valid experiment requires a detailed procedure. The procedure should include all steps of the lab in such detail that anyone can repeat the lab (even if they have no previous knowledge of how to do the lab).

As part of the procedure, the experiment needs repeated trials of the data collection. It would not be valid to test the effects of tobacco smoke on just one frog and to say those results are normal for all frogs. Just as it would not be valid to have an Olympic sprinter run once around a track and then state that all the people in the world can run the same distance in the same time

Many subjects should be tested and the test should be repeated several times to see if the results are valid for all. There also needs to be controls in the experimental procedure These are also called the constants. There should be no other variables except the one you are testing.

In the example given, all the frogs should be given exactly the same amount of tobacco smoke, at the same time of day, in the same size container. That way, any change in lung capacity among the frogs will be due to just to the smoke and nothing else.

Homework Answer questions 1-4 on the notes. Don’t forget to bring an a magazine ad that makes a testable claim by Thursday.