October 2026 - Scientific Reasoning Study Guide

The scientific method

Not a rigid recipe, but the exam tests the order and the vocabulary.

1. Observe
2. Question
3. Hypothesis
4. Experiment
5. Analyse
6. Conclude
7. Report

The three kinds of variable

Every experimental design question comes down to sorting these correctly.

• Independent — the one thing the researcher deliberately changes.
• Dependent — what is measured in response to that change.
• Controlled — everything deliberately held constant so it cannot explain the result. Temperature, timing, the equipment used, who does the measuring.
• Only one independent variable at a time. Change two and no result can be attributed to either.

Why a control group is not optional

The control group receives no treatment, or a placebo, and everything else about it matches the experimental group. It exists to answer a question the treated group cannot: what would have happened anyway?

Without it, an improvement means nothing. Patients recover on their own, symptoms fluctuate, and people who know they have been treated report feeling better. A control group is the only way to separate the effect of the treatment from all of that — and questions often hinge on spotting that a described study has no control at all.

Hypothesis, theory and law

These are not stages of certainty in the way everyday speech suggests. They are different kinds of statement.

Reliability and validity

Both words appear in answer choices and they mean different things.

What weakens a study

These are what "which of the following is a limitation" questions are pointing at.

• No control group — nothing to compare the outcome against.
• A small sample — results may be chance, and cannot be generalised.
• Confounding variables — something else changed at the same time.
• Bias in selection — the groups differed before the study began.
• No blinding — expectation shapes what participants report and what researchers record.
• Correlation read as cause — the most common error of all.

Evaluating a described study

Reading data and measurement

• Qualitative data describes; quantitative data counts or measures.
• Accuracy is closeness to the true value; precision is consistency between repeated measurements. A measurement can be precise and wrong.
• Always check the units and the scale before comparing figures.
• A conclusion may not extend beyond the population that was studied.

Terms to know

Hypothesis

A testable, falsifiable prediction.

Theory

A well-supported explanation of why something happens.

Scientific law

A reliable description of what happens, without explaining why.

Independent variable

The one factor deliberately changed.

Dependent variable

What is measured in response.

Controlled variable

A factor held constant so it cannot affect the result.

Control group

An untreated or placebo group used for comparison.

Placebo

An inactive treatment given so the comparison group has the same experience.

Confounding variable

An uncontrolled factor that could explain the result.

Reliability

Consistency of a measurement on repetition.

Validity

Whether a measurement captures what it claims to.

Peer review

Evaluation by other specialists before publication.

What the TEAS asks most

The same core ideas appear in different wording. If you can answer these without stopping to think, you have what this section requires.

Key points

• Change one variable at a time and hold the rest constant.
• Independent is changed, dependent is measured, controlled is held steady.
• A control group is what makes a result interpretable.
• A hypothesis must be testable and falsifiable.
• A law describes; a theory explains. Reliability is consistency, validity is measuring the right thing.

Review quiz

5 questions on this topic, each with the reasoning worked through. Pick an answer to see how it went, or open the explanation straight away.

1. Question 1 of 5

   A researcher tests whether a hand cream reduces skin dryness. One group uses the cream, another uses an identical cream without the active ingredient. What is the second group called?

   Answer choices for question 1

   A The experimental group B The control group C The independent variable D The confounding variable
   Show the answer and explanation

   Correct answer: B. The control group

   A group receiving an inactive version exists purely for comparison, which makes it the control — and using an identical-looking cream keeps the experience the same. The experimental group receives the active treatment, while a variable is a factor rather than a group of participants.

2. Question 2 of 5

   Which of the following is a properly formed hypothesis?

   Answer choices for question 2

   A Handwashing is important for patient safety. B Washing hands with soap for 20 seconds reduces bacterial counts more than rinsing with water alone. C What effect does handwashing have on infection? D Everyone should wash their hands more often.
   Show the answer and explanation

   Correct answer: B. Washing hands with soap for 20 seconds reduces bacterial counts more than rinsing with water alone.

   It names a specific comparison and a measurable outcome, so a result could show it false — which is what makes a hypothesis testable. The first is an untestable value statement, the third is the research question rather than a prediction, and the fourth is a recommendation.

3. Question 3 of 5

   A study finds that patients who eat breakfast have fewer falls. The authors conclude that eating breakfast prevents falls. What is the flaw?

   Answer choices for question 3

   A The sample was too large. B It treats a correlation as though it established causation. C Falls cannot be measured accurately. D Breakfast is not a variable.
   Show the answer and explanation

   Correct answer: B. It treats a correlation as though it established causation.

   Patients well enough to eat breakfast may simply be less frail, which would produce the same association without breakfast causing anything. A large sample is a strength rather than a flaw, falls are routinely recorded, and breakfast is a perfectly workable variable.

4. Question 4 of 5

   A set of scales gives a reading of 71.2 kg every time the same patient is weighed, but the patient actually weighs 68.0 kg. How should the scales be described?

   Answer choices for question 4

   A Accurate but not precise B Precise but not accurate C Both accurate and precise D Neither accurate nor precise
   Show the answer and explanation

   Correct answer: B. Precise but not accurate

   Repeating the measurement gives the same figure each time, which is precision, but that figure is more than three kilograms from the truth, so accuracy fails. This is exactly why consistency alone is not evidence that an instrument is right.

5. Question 5 of 5

   What is the difference between a scientific theory and a scientific law?

   Answer choices for question 5

   A A theory becomes a law once enough evidence supports it. B A law describes what happens; a theory explains why it happens. C A theory is a guess; a law is proven. D A law applies only to physics; a theory applies to biology.
   Show the answer and explanation

   Correct answer: B. A law describes what happens; a theory explains why it happens.

   The two answer different questions and neither is a stage on the way to the other. A theory is not a guess — that is a hypothesis — and both terms are used across every scientific discipline.

Put this TEAS topic into practice

Build a set on scientific reasoning and use the rationale on every question to reinforce what you just reviewed.

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