Experimental Skills and Scientific Enquiry
This domain tests experimental design, data handling and evaluation. Questions ask you to identify variables, improve reliability and validity, interpret graphs and recognise sources of error.
Variables and design
The independent variable is changed; the dependent variable is measured; control variables are kept constant. A control group is a comparison without the treatment. Reliability improves with repeats and means. Validity depends on measuring the intended variable and controlling confounders. Accuracy is closeness to the true value; precision is closeness of repeats.
Data and evaluation
Use line graphs for continuous data and bar charts for categories. Include units, label axes and identify anomalies. Calculate means and ranges. Sampling must be random to avoid bias. Report uncertainty when appropriate.
Worked example
An experiment measures the time for starch to disappear at different temperatures. The independent variable is temperature; the dependent variable is time; control variables include pH, enzyme concentration and starch volume. Repeat each temperature and calculate a mean. Reasoning: controlling these variables ensures any change in time is due to temperature, improving validity.
Traps
- 'Control' can mean a control group or a controlled variable; read the question carefully.
- Repeats improve reliability, not necessarily accuracy.
- A correlation does not prove causation.