Key terms in practical science

• Variable


  Anything that has the potential to change. In an experiment, we normally measure how changing one variable affects another.
• Independent variable


  The variable that is changed in an experiment. For example, the amount of water given to the plants.
• Dependent variable:


  The variable that is measured in an experiment. For example, the height of the plants.
• Controlled variables


  The variables that are kept constant during an experiment. For example, the amount of sunlight, temperature, soil pH or plant type.
• Control


  A group which is treated exactly the same as the experimental group, except it doesn’t receive any treatment that’s expected to cause an outcome. For example, a plant that receives no water.
• Hypothesis


  A testable prediction for what will happen in an experiment. For example, we might hypothesise that if there is a positive relationship between the amount of water given to a plant and its height, then plant height will increase as the amount of water it receives increases.
• Quantitative


  Variables, measurements or data that are numerical. These are characterised by their quantity rather than their quality. For example, plant height can be measured using a ruler, giving a numerical value in centimetres.
• Qualitative


  Variables, measurements or data which aren’t numerical. These are characterised by their qualities, so by classification into a certain type or category. For example, plant height could be measured subjectively in terms of "very short", "short", "medium", "tall" and "very tall".
• Validity


  A measure of how well an experiment tests the hypothesis.
• Accuracy


  A measure of how close a measured value is to the true value.
• Reliability


  A measure of the consistency of measurements.

  Reliability is a general term that has three specific elements:

  • Precision: A measure of how close multiple measurements are to each other.
  • Repeatability: A measure of the consistency of measurements between multiple experiments carried out by the same person with the same method and equipment.
  • Reproducibility: A measure of the consistency of measurements between experiments carried out by different people with slightly different equipment.
• Correlation


  The relationship between our independent and dependent variables. Broadly, variables can be positively or negatively correlated, or sometimes not correlated at all!
• Causation


  The action of causing something. In other words, how cause is related to effect.