The amount of Hormone X that was administered to each treatment group was the single independent variable of this experiment, because it was the only experimental factor deliberately varied between treatment groups. Dependent variables are those characteristics or features of a population which have the potential to respond to the experimental conditions imposed . The weight of each chick following administration of Hormone X is the dependent variable in the example presented. There may be many dependent variables in an experiment, not all of which are either known by the investigator or considered important . In the above example, it is possible that the size and weight of the chicks' livers may be increased by Hormone X. Depending upon the hypothesis and goals of the experiment, this may either be an important dependent variable or of no immediate concern to the investigator.
Constants are factors or conditions which are the same across all treatment groups .
In the current example, access to water, feeding time, size of pen, etc. were conditions which were applied to all groups of chicks. The group of chicks which received feed without Hormone X included was the control group and used as a reference for assessing effects of Hormone X on weight or color of the other treatment groups. A simple definition of a repeated trial would be the collection of multiple measurements of a given characteristic or phenomenon. In actuality, a repeated trial can take many forms. In the above example each individual chick itself is a repeated trial for determining change in weight.