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​Controlled experiments and hypothesis formulation

Once a topic has been identified students develop a research question for investigation, which may involve formulating a hypothesis.

Teachers should guide students so that they do not proceed with a research question or hypothesis that is not testable.

Variables

The formulation of a hypothesis includes the identification and control of variables. A variable is any quantity or characteristic that can exist in differing amounts or types and can be measured. Values for variables may be categorical or they may be numerical, having a magnitude.

Not all variables can be easily measured. Length can be measured easily using, for example, metre rulers. Shades of colour are less easily measured and are more likely to be subjective. They might be measured by, for example, using photographic comparisons to produce a set of graduated ‘standards’ that are nominated and named for the purposes of the investigation.

In VCE Environmental Sciences, students are required to identify independent and dependent variables. They should also understand the need to control other variables (extraneous variables including confounding variables) that may affect the integrity of the experiment and the interpretation of results. Operationalisation of variables is beyond the scope of the VCE Environmental Science Study Design.

Concepts related to variables that apply to VCE Environmental Science are specified in Defining variables.

Developing a testable hypothesis​

A hypothesis is developed from a research question of interest and provides a possible explanation of a problem that can be tested experimentally. A useful hypothesis is a testable statement that may include a prediction. In some cases, for example in exploratory or qualitative research, a research question may not lend itself to having an accompanying hypothesis; in such cases students should work directly with their research questions.

There is no mandated VCE Environmental Science ‘style’ for writing a hypothesis. Recognition of null and alternate hypotheses, one- and two-tailed hypotheses, and directional and non-directional hypotheses is not required.

The following table provides an example of how a hypothesis may be constructed from a research question using an ‘If-then-when’ construction process:

Step 1:  Ask a research question of interest: Is there a difference in rainfall over adjacent rural and urban towns?

Step 2: Identify the independent variable (IV): type of land mass (rural or urban)

Step 3: Identify the dependent variable (DV): rainfall

Step 4: Construct a hypothesis (a – f below):

a b c d ef
If… the DV)…relationship phrase to the IV​…then…trend indicator effect on the DV​…when…trend indicator action by the IV

…depends on…

…results from…

…is affected by…

…is directly related to…

​...show an increase/ decrease ...

...be greater than/ less than...

...be larger/smaller...

...increased/ decreased...

...greater/less...

...large/small...

Hypothesis: If the rainfall over a land mass is directly related to the degree of urbanisation, then the rainfall will be greater in urban towns when compared with rural towns.

Notes:

  • Different writing styles for hypotheses can be equally valid.
  • Some hypotheses include reasons for the inherent prediction, for example, the above hypothesis may be extended as: ‘If the rainfall over a land mass is directly related to the degree of urbanisation, since urban areas heat up more than rural areas because of the heating differences of two surace types, then the rainfall will be greater in urban towns when compared with rural towns.’
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