Parts of the Controlled

Experiment

Hypothesis: a possible answer to a question Example of a

Hypothesis: It is possible that

dogs eat grass because they need some green plants in their diet.

A good hypothesis can be tested with an experiment In a controlled

experiment, one factor is changed to observe the effect on another factor while all other factors are kept constant.

An Example of a Controlled Experiment: Ten dogs of the same breed and age are fed

the same amount of dog food each day. Five of the dogs eat dog food containing

vegetables and the other five eat dog food that is made of meat only.

All dogs are allowed outside in the grass for the same length of time each day.

All dogs are observed to see if they eat grass.

A variable is a factor that may change in an experiment.

There are two variables in a controlled experiment:

The independent variable

And the dependent variable

The independent variable is changed on purpose by the scientist. What is the

independent variable in the dog food experiment?

Vegetables in the dog food was the factor that was made different in the two groups of dogs.

The Dependent Variable is measured or observed by the scientist to see if it was affected by the experiment. What was the

dependent variable in the dog food experiment?

Eating grass was measured or observed by the scientist to see if there was an affect on this behavior.

The constants in the experiment are kept the same so only one variable could affect the results of the experiment.

Can you list the constants in the dog food experiment?

Breed of the dog Age of dog Amount of dog food Amount of time in

the grass

The control group

Why did we have two groups of dogs?

Why not just observe one group of dogs?

The control group is there for comparison.

The data are pieces of information collected during the experiment.

Data analysis is when you work with the data.

Data analysis might mean doing some math, like Taking averages Calculating percent

Then you can make statements like these:

The dogs on a vegetable diet were observed eating grass an average of 2 times.

For the dogs without a vegetable diet, the average was > 4 times, over 100% more.

A conclusion is a statement based on the results of the experiment.

The results (the data) of the experiment are analyzed.

The hypothesis is either accepted or rejected.

Then a conclusion can be made.

An inference is when you make a BIG statement about all dogs… …not just the ones in your experiment. This is where sometimes a scientist gets it

wrong. Just because the 10 dogs in this

experiment gave you certain results, doesn’t always mean that ALL dogs will be the same.

If there was no difference in the grass eating habits of the two groups of dog….

The hypothesis would be rejected and

the scientist might infer that a dog’s diet does not affect grass eating.

If the dogs that were on a diet that included vegetables ate less grass than the other dogs……. The hypothesis

would be accepted. The scientist might

infer that dogs eat grass because they need some plant material in their diet.

Communication

Scientists share their findings with each other by publishing papers that describe their work.

What do you need to know for class? What are the meanings of the following terms? Controlled experiment Independent/Dependent variable Control group Constants Data / Data Analysis Conclusion/Inference