Control Group

• When you create a scientific experiment, it is important to include a control group, in which conditions are not altered in any way. The components of this group should be left as nature made them. For instance, if your question is whether fertilizer makes plants grow better, your control group would be a pot of plants that has not been fertilized. The control group should involve conditions that are as natural and normal as possible.
  
  

Constant Factors

• For each experiment, there will be control factors that will be the same for each group within your experiment. For instance, in the case of plants and the effects of fertilizer, one group would use fertilizer and the other would not. However, to make the experiment as fair and accurate as possible for each group, some factors must be the same. Plant the same type of vegetation, preferably from the same seed packet. Use the same soil and the same amount of water for each group, and place each in the sun for the same amount of time.
  
  

Environmental Factors

• While it can be difficult to control the environmental factors for your experiment, it is important to do your best to make these factors as consistent as possible. You cannot control how many days will be sunny and how many days will be cloudy or rainy. What matters, though, it that each experimental group is exposed to the same weather conditions for the same amount of time. This matters in all experiment types, whether you are dealing with temperature, weather or other variable environmental factors.
  
  

Repeated Experiments

• In some situations, it is best to repeat an experiment to verify your results. It is important when you go through the experimental process that you take thorough notes on all aspects of the experiment, such as the environmental elements, what you tested and what the results were. When you repeat the experiment, follow your notes and complete the experiment as closely to the same way as possible. In some cases, the results will be exactly the same. In others, the results may vary, which can skew your experimental results. However, having a mix of results can help you confirm or disprove your hypothesis.