The scientific method outlines the correct way of performing scientific experiments in order to get unbiased and reliable results.

There are two main types of scientific experiments commonly used in science fair projects:

The purpose of a controlled science experiment is to find out what happens to something if you change something else while you keep all other things unchanged.

Say you want to test the effect of a certain fertilizer on radish plants growth. For this you need to create two groups of radishes: the control group and the experimental group. The two groups are treated the same (irrigation, light, etc.) besides only one factor, the fertilizer in question which is applied only to the radishes belonging to the experimental group.

The fertilizer applied is called the independent variable (independent of any experiment factor and is decided only by your free choice) whereas the result, the growth rate of the radishes in the experimental group, is called the dependent variable (the outcome depends on the independent variable).

In an controlled experiment you can test only one independent variable. That means that you can only change one condition in your experiment. If there's more than one independent variable in an experiment it becomes flawed. If you want to test another independent variable, you'll have to conduct another experiment. For example, if in our experiment, in the experimental group, besides the fertilizer also the amount of light is not the same as in the control group then it's impossible to deduce which condition affects the radish plants growth - the fertilizer or maybe the light intensity.

The purpose of a comparative experiment is to compare the effect of two or more different things on something.

Suppose you want to investigate the effect of irrigation method (flood, spray or drip) on the growth rate of radishes.

In this experiment you need three experimental groups, each for every irrigation method (flood, spray or drip) and in this case you don't need a control group at all. In this experiment the irrigation method is the independent variable and the resulting growth rate of the radishes is the dependent variable. Treat each group of plants the same (light, water quantity, nutrition, cultivation, etc.) besides your independent variable - the different irrigation method.

In an comparative experiment you can test, of course, the effect of a few independent variables but not in the same experimental group where also only one independent variable is allowed as in the case of a controlled experiment.

The Sections of an Experimental Science Fair Project Report

That's a general science fair project outline requested by most teachers, competitions and judges.

Suppose your research question for an experiment is, "what is the effect of the irrigation method (flood, spray or drip) on the growth rate of radishes?" The hypothesis might be "drip irrigation is the best method for the growth rate of radishes" (don't say drip irrigation is the best for radishes since best can't be measured but, on the other hand, you can measure the growth rate of radishes in cm.)

Remember, sometimes an experiment disproves the hypothesis and it doesn't mean that your project failed, it could mean that maybe you have just discovered something new (bravo!) and you can be still awarded the 1st place on the condition that your experiment is correctly performed accordingly to the scientific method principles.

Remember that the hypothesis is a crucial element of the scientific method since the hypothesis could be proved or refuted by statistical means.

Take in consideration the sample size of your experiment. A too small sample can result in casual results and a too big one can result in over population effects (if you experiment with plants or animals).

In order to avoid coincidental effects on your experiment you will need to repeat your experiment a few times – this procedure is called repetitions.

Take in account time constrains. If you only have a few weeks at your disposal to perform your experiment, don't decide on a procedure that will take months to carry out.

Write down your procedure accurately thus you, or somebody else, can follow it in order to repeat the experiment.

Keep all your results in one notebook (logbook / journal) for future use.

"Results" comprise the data collected during the experiment. On the other hand the "conclusions" is what you learned from this data and what the results mean.

In brief, you have to state whether the experiment outcomes agree with your hypothesis. If not, that's an acceptable result too, and it doesn't mean that the experiment failed (on the condition that your experiment sticks to the scientific method guidelines).

Also consider other possible explanations for your results (desirable or undesirable). Did you unintentionally expose your plants to winds or insects or your animals to unexpected noise and other disturbances that could affect your experiment outcomes?

It is also recommended to mention additional experiments needed in order to investigate your topic further, and also your experiment limitations if you identify such (conditions or factors that you cannot satisfactory control in an experiment).

The "conclusions" could be regarded as a summary of your project.