Research Question: “How effective are plant-based insect repellents?”
Independent Variable Possible Dependent Variables
Different brands of plant-based repellents
(ideally with differing levels of the active
ingredient)
• Total number of insect bites
• Size of insect bites
• Color and/or itchiness of insect bites
• Length of time
Experimental Groups
Experimental groups are the treatment groups or trials that receive all of the
same conditions, except varying amounts or qualities of the independent variable.
Experimental groups are sometimes called treatment groups because they
receive the change of the independent variable. An important component of
designing strong experiments is replication (i.e., performing an experiment
more than once). In some STEM experiments, experimental groups containing
several entities can be running at the same time, while other experiments
will have multiple trials, or runs, that are conducted periodically over time.
The word trials refers to the number of treatment replications that you
perform on experimental and control groups. Having multiple entities in
each experimental group or running multiple trials is important because it
decreases the influence of variations associated with the independent variable,
researcher measurement error, and difference between the entities studied.
For example, in a biology experiment with seeds and pH, four experimental
groups, each with multiple seeds, can be set up at the same time, each with
different pH levels, and data can be collected from each of the groups at regular
intervals throughout the experiment. But an engineering research project
testing the mechanical advantage of differing arm lengths of a catapult would
use multiple trials of each arm length, which would require making adjustments
to the catapult in between experimental groups.
By doing thorough background research, you should be able to determine
both how many experimental groups to have and the appropriate levels
of the independent variable for each of the groups. The organization of the
experimental groups is critically important for a strong research design. Having
experimental groups that are not varied enough in quantity or quality
may not show any change in the dependent variable and, therefore, will not
help you determine any connection between your independent variable and
dependent variable. Let’s look at an example. The following hypothesis is
testing to determine a relationship between levels of vitamin C and when a
fruit is picked.