Scientific Investigation and School-Based Assessment
Scientific Investigation and School-Based Assessment assesses whether you can plan, carry out and report an investigation. It covers hypotheses, variables, controls, sampling, replication, risk assessment, data analysis and scientific writing.
Core rules
- A hypothesis is a testable prediction linking independent and dependent variables; it must be falsifiable.
- Identify the independent variable, dependent variable and at least three controlled variables; a control group receives no treatment or a standard treatment.
- Operational definitions specify how variables are measured, e.g., “rate of photosynthesis = number of bubbles per minute”.
- Replication and random sampling reduce bias; repeated measurements improve reliability; calibration improves accuracy.
- Choose statistics to match the data: t-test for comparing two means, chi-square for categorical frequencies, correlation for relationships.
- Report includes aim, hypothesis, variables, method, results, analysis, conclusion, evaluation and references.
Worked example
A student tests light intensity on pondweed photosynthesis. Independent variable: distance of lamp from the plant (10, 20, 30, 40 cm). Dependent variable: bubbles counted per minute. Controlled variables: temperature, CO2 concentration, pondweed length, lamp type. Reasoning: distance is a proxy for light intensity, but heat from the lamp can confound the result, so a transparent heat shield or water bath is needed. Count bubbles for three minutes and repeat at each distance; use the mean rate.
Traps
- A controlled variable is held constant; a control group is a comparison treatment.
- Correlation does not prove causation.
- A p-value below 0.05 suggests the observed difference is unlikely under the null hypothesis; it does not prove the hypothesis is true.