In the Mega Gro experiment discussed below, the plants might be matched according to characteristics such as age, weight and whether they are blooming.This involves distributing these plants so that each plant in one group exactly matches characteristics of plants in the other groups.
For example, if you remove a loud noise from the room, will the person next to you be able to hear you?
Or how much noise needs to be removed before that person can hear you?
Selecting groups entails assigning subjects in the groups of an experiment in such a way that treatment and control groups are comparable in all respects except the application of the treatment.
Groups can be created in two ways: matching and randomization.
In the example used in this guide (you'll find the example below), we discuss an experiment that focuses on three groups of plants -- one that is treated with a fertilizer named Mega Gro, another group treated with a fertilizer named Plant!
, and yet another that is not treated with fetilizer (this latter group serves as a "control" group).
An experimenter who wants to show that adding a certain fertilizer will help a plant grow better must ensure that it is the fertilizer, and nothing else, affecting the growth patterns of the plant.
To do this, as many of these variables as possible must be controlled.
The amount that you turned the knob is the independent variable, the variable that the researcher controls, and the amount of sound that resulted from turning it is the dependent variable, the change that is caused by the independent variable.
Experimental research also looks into the effects of removing something.