- 1). Decide on the focus of the experiment. If you are working as a group, arrange a time for your group to discuss various options. If you are a student, you may have detailed instructions about the kind of experiment that is required or have more or less free reign. Choose something relevant to the course that has not already been covered in a class experiment. For example, if you are studying how plants grow, you may wish to investigate the effects of varying levels of heat, light, water or nutrients.
- 2). Select one independent variable (the variable you control) of the topic to investigate; for example, nitrates and one dependent variable (the effects); for example, the rate of plant growth. An experiment with two independent variables is possible, but you will need to carry out a larger number of replications to cover all possible combinations of the two variables.
- 3). Research the topic through background reading, outside of your course books, to see what is already known on the topic. Your school library and the Internet are good starting points.
- 4). Create a hypothesis of the results you think the experiment will produce, based on your knowledge of the topic. For example, a hypothesis for nitrates and plant growth is that your plants will grow faster with higher levels of nitrates, and slower at lower levels. It doesn't matter whether your hypothesis is proved right or wrong, you have still answered the question.
- 5). Decide on the procedure and equipment, choosing the simplest and fastest way to investigate your hypothesis. For example, you might test zero levels of nitrates, the average level for soil in the plants' natural habitat, a level significantly below this and a level significantly above this. Decide how many replications you will do. Most experiments need at least 10 replications.
- 6). Discuss with your group which other variables might affect your experiment. Consider how to ensure they remain the same or how to reduce them. Adapt your procedure accordingly. For example, you could eliminate the effects of genetic variation on how quickly the plants grow by using cuttings rather than seeds.
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