Also can be referred to as responding variable or the variable which is
measured / directly observed by the experimenter.
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Can be known as either Fixed or Controlled variables. Variables other than the experimental variable could also affect the outcome of the experiment. These need to be controlled or kept constant so that only one variable is being investigated at a time. Many scientific investigations have fallen down when not every significant variable was successfully controlled.
There are two major types of variables here that need to be controlled:
Living organisms vary from each other in the following ways:
Genetic variation
Individual behaviour
Differences in fitness
Differences in their immediate environment
If organisms are used in the experiments then many of the variables relating to them will need to be controlled. If the investigation uses small numbers in the sample size then all due care needs to be taken to ensure that the control group and experimental group are matched as closely as possible with regard to things such as the number of organisms, their age, size, sex and any other relevant characteristics.
If a very large sample size are used then these variables often average themselves out. (i.e. you can compensate for individual differences by having a large, representative/random sample)
In all experiments the environmental factors will need to be controlled as much as possible.
This is much easier to achieve if the investigation is carried out in a laboratory environment but not as easy in a field situation. Different problems may arise.
In a laboratory situation factors such as temperature, light, dosage of a chemical, amount of food and water administered can be controlled easily.
In a field situation these factors may have diurnal or seasonal variation depending on the length of the experiment. The variations are “controlled” in the sense that the variation affects the organisms to the same extent if the locations of the trials are similar. However it does mean that some monitoring of these variables will need to be taken into account and also the
selection of the experimental sites such as random placing etc.
