Experimental design: variables

Independent and dependent variables

The independent variable is the cause of the dependent variable. For example, a litre of water is added to 2 plants every day, resulting in the plants growing taller, having more leaves and damper soil. In this example, the litre of water is the independent variable because it causes the plants to grow taller, have more leaves and damper soil.

The dependent variable is the effect of the independent variable. For example, a litre of water is added to 2 plants every day, resulting in the plants growing taller, having more leaves and damper soil. In this example, the effects of the litre of water (taller, more leaves and damper soil) on the 2 plants is the dependent variable because it is the effect.

Types of data: First-hand, second-hand, qualitative, quantitative

First-hand data is data people collect on their own. Examples include counting, conducting polls or experiments or using measuring devices.

Second-hand data is data collected by someone other than yourself. Examples include encyclopedias, newspapers, reference books and the internet.

Qualitative data is data represented by qualities or characteristics rather than numbers. Examples include colour, temperature or texture. Quantitative data is data represented by numbers. Examples include a certain temperature, amount or distance.

Control, aim, hypothesis, results, materials, method, discussion and conclusion.

Control: the element in an experiment that remains unchanged or unaffected by other variables. For example, if I were to conduct an experiment on plants growing faster in sunlight then the control would be the sunlight.

Aim: the aim in an experiment is a single statement that describes the purpose or reason to why the experiment is being conducted.

Hypothesis: A statement about a specific research question that outlines the expected result of the experiment. Example - plants grow faster in the sunlight.

Results: The results of the experiment.

Materials: The materials used to conduct an experiment.

Method: The way an experiment is conducted.

Discussion: An analysis of the experiment.

Conclusion: A conclusion is a statement based on experimental measurements and observations. It includes a summary of the results, whether or not the hypothesis was supported, the significance of the study, and future research.

Observations vs inferences

An observation is using your senses to collect or record information. An inference is an informed guess about observations you make.