The scientific method is the process used to set up a controlled experiment to test observations of the natural world.


Steps of the scientific method:

1. Asking the question:

      used to identify the problem.

     obtained by making observations (the act of noticing and describing events or processes in a careful, orderly way).

     the information gathered from observations is called data.

EX: Researchers observed that marsh grasses grow taller in some placed than others.

Example Problem:

Why do marsh grasses grow to different heights in different places?


2. Forming the hypothesis:

     a proposed scientific explanation for a set of observations that can be tested.

     usually answers the question you were asking.

     hypotheses are formed by making inferences (a logical interpretation based on prior knowledge or experience).

Example Problem:

Why do marsh grasses grow to different heights in different places?

Example Hypothesis:

If marsh grasses grow to different heights in different places, then marsh grass growth is limited by available nitrogen.


3. Setting up a controlled experiment:

     a procedure that tests a hypothesis by the process of collecting information under controlled conditions.

     controlled experiments contain two types of groups: the control group and one or more experimental groups.

     the factors in an experiment that can change are called variables.


Control group: the standard for comparison, all the variables are kept the same.


Experimental group(s): the test group(s), all variables are kept the same except the one variable being tested (the manipulated variable).


Manipulated (or independent) variable: the variable in an experiment that is deliberately changed.


Responding (or dependent) variable: the variable that changes in response to the change in the manipulated variable. This is the variable that is observed.


NOTE: In a controlled experiment, only one variable should be changed at a time. All other variable should be kept unchanged or controlled!


EX: The researchers selected similar plots of marsh grass. All plots had similar plant density, soil type, input of freshwater, and height above average tide level. Plots were divided into control and experimental groups.

Researchers added nitrogen fertilizer to the experimental plot but left the control plot alone. They then observed the growth of the marsh grass in both plots.


What is the manipulated variable in this example?

The addition of nitrogen fertilizer

What is the responding variable in this example?

The growth of the marsh grass


4. Record and analyze results:

A. Numerical data or quantitative data:

     can be measurements or numbers of things.

     usually recorded in tables or charts and then a graph of the data is made.

     always measured in the metric system or the international system (SI).


B. Descriptive data or qualitative data:

     expressed in verbal form to describe observations made during the experiment.


EX: Title: The effect of the amount of nitrogen on marsh grass growth.

Amount of Nitrogen

Marsh Grass Growth (cm)

Trial 1

Trial 2

Trial 3







No Nitrogen






Analysis: The marsh grass grew taller when fertilizer with nitrogen was added to the soil.


5. Draw a conclusion:

     restate the hypothesis.

     Was the hypothesis supported by the data or not?

     Use the results to explain how the hypothesis was supported or not?

     Were there any experimental errors in your procedure? What could have been done differently?

     How might you use these results to make new predictions and do further experiments?


For Example: The original hypothesis was If marsh grasses grow to different heights in different places, then marsh grass growth is limited by available nitrogen.(1 point) The hypothesis was found to be correct. (1 point) The average marsh grass growth for adding nitrogen was 27.7 cm but the average marsh grass growth for not adding nitrogen was 17.7 cm (2 points) When CaCl2 is added to water, the bonds are broken. (1 point) Plants need nitrogen to make two very important compounds, DNA and proteins. Without DNA and proteins, new cells can not be made and therefore, the plant cannot grow taller. (1 point) Possible experimental errors were that is was difficult to control all of the factors that should have been constants when growing marsh grass outside. A better way to conduct this experiment would be to grow marsh grass in a laboratory under controlled conditions so all of the factors except amount of nitrogen can be constant.(1 point).


6. Reporting and verifying the results:

     It is very important to report your findings in a scientific journal so other scientists can examine it for flaws.

     An experiment is verified when other scientists peer review the experiment and get the same results. (standard NoS 4)

     An experiment is only considered valid after is has been verified by a scientistís peers.

     Peer review allows the experiments to be examined for oversights, unfair influences, fraud or mistakes in techniques or reasoning.