Accuracy, reliability and validity appear regularly in VCE Chemistry exams, particularly in questions linked to experimental design, data interpretation, and evaluation of results. Despite this, the 2024 Chemistry Examiner’s Report shows that many students continue to conflate these terms or apply them in ways that are not supported by the context of the question.
What makes these questions especially punishing is that students often demonstrate partial understanding. Their answers sound scientific, but one conceptual slip is enough to cap the response.
Accuracy is about closeness to a true value, not consistency
The most common error identified in the 2024 Examiner’s Report is students using accuracy and reliability interchangeably.
Accuracy refers to how close a measured value is to the accepted or true value. In exam questions, this true value may be explicitly stated, implied through a known constant, or inferred from theoretical expectations.
Many students correctly identify a source of systematic error, such as heat loss or calibration issues, but then conclude that the results are unreliable. This is incorrect. Systematic errors affect accuracy, not reliability.
In the 2024 exam, responses that identified a systematic bias but linked it to reliability were routinely capped, even when the rest of the explanation was sound. This shows that Chemistry marking does not reward general correctness. It rewards conceptual alignment.
Reliability is about repeatability, not correctness
Reliability refers to the consistency of results when an experiment is repeated.
A recurring issue noted in the Examiner’s Report is students describing a lack of accuracy and then concluding that the results are unreliable. For example, students explained that an experimental setup consistently underestimated a value and then claimed this reduced reliability.
If results are consistently wrong in the same way, they may still be reliable. They are inaccurate, but reliable.
High-scoring responses in the 2024 exam explicitly linked reliability to spread, scatter, or variation in results, often referring to repeated trials or consistency between measurements.
Students who did not refer to repeatability or variation were rarely awarded full marks for reliability explanations.
Validity depends on whether the experiment tests what it claims to test
Validity is the least well understood of the three terms and the one most often omitted or misused.
Validity refers to whether the experimental design actually measures the intended variable. In the 2024 exam, validity appeared implicitly in questions where students were asked to evaluate experimental methods or data.
Many students focused on accuracy or reliability when the question was actually about validity. For example, they discussed measurement precision when the core issue was whether the method isolated the variable being investigated.
Examiner’s Reports note that responses which failed to address whether the experiment measured the intended relationship were capped, even when other evaluative comments were correct.
Validity requires students to think about experimental design, not just data quality.
Students often explain the error but not its consequence
Another pattern identified in the 2024 Examiner’s Report is students correctly identifying a flaw but failing to explain how it affects accuracy, reliability or validity.
For example, students might state that heat was lost to the surroundings but not explain whether this led to an underestimation or overestimation of the measured value. Without this link, the explanation is incomplete.
Full-mark responses always connected the source of error to its impact on the outcome.
Context matters more than definitions
One reason students struggle with these terms is that they memorise definitions but do not practise applying them in context.
In the Chemistry exam, students are not asked to define accuracy, reliability or validity. They are asked to apply them to specific experiments, data sets, or procedures.
The 2024 Examiner’s Report explicitly indicates that responses relying on memorised definitions without contextual application were not rewarded.
High-scoring responses embedded the term naturally within the explanation and demonstrated understanding through application rather than definition.
Why students default to the wrong term under pressure
Under exam pressure, students often choose the term that feels most familiar. Accuracy is often overused because it feels intuitive. Reliability is often used because it sounds scientific. Validity is often avoided because students are unsure how to apply it.
This leads to responses that are fluent but misaligned.
The Chemistry exam is designed to detect this. It discriminates between students who know the terminology and students who can apply it precisely.
How students should be answering these questions
Effective responses follow a clear reasoning path.
They:
- identify the flaw or feature of the experiment
- decide whether it affects closeness to the true value, consistency, or experimental purpose
- use the correct evaluative term
- explain the impact in context
These responses are often short. Length does not compensate for incorrect classification.
How this shows up across exam years
While the 2024 Examiner’s Report is particularly explicit, similar commentary appears in earlier reports. Accuracy and reliability confusion is not new, and it remains one of the most reliable ways the exam differentiates students.
This consistency means students can prepare for these questions with confidence, provided they practise applying the terms correctly.
An ATAR STAR perspective
ATAR STAR treats accuracy, reliability and validity as applied reasoning tools rather than vocabulary items. Students practise diagnosing experimental flaws and deciding which evaluative concept actually applies before they write anything.
This approach benefits high-performing students who want to avoid capped responses, and developing students who need a clearer framework for evaluation.
In VCE Chemistry, knowing the definitions is not enough. You must know when and how to use them.