Year 9 Science Unit 1 · Disease Lesson 18 of 20 45 min SC5-DIS-18

Investigating Disease

How do we know what causes disease? How do we know if a treatment works? Behind every medical breakthrough is a carefully designed investigation. Learning to think like a scientist — to ask good questions, design fair tests, and interpret evidence — is one of the most powerful skills you can develop.

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Think First

Before You Begin

Imagine you notice that students who eat lunch in the cafeteria get stomach aches more often than those who bring lunch from home.

Write down your answers before reading on:

  • What question could you investigate?
  • How would you design a study to test your idea?
  • What data would you need to collect?
Write your thinking in your book before reading on.

Work mode: Digital — answers typed below

Learning Intentions

Know

  • The steps in scientific investigation of disease
  • What case-control and cohort studies are
  • Key ethical principles in medical research

Understand

  • Why controlled experiments are necessary to establish cause and effect
  • How bias can affect research results
  • The importance of sample size and randomisation

Can Do

  • Design a fair test to investigate a disease-related question
  • Analyse simple disease data
  • Evaluate the ethics of a research proposal
Key Terms
Hypothesis A testable prediction about the relationship between variables.
Independent variable The factor that is deliberately changed in an investigation.
Dependent variable The factor that is measured or observed in an investigation.
Controlled variable A factor that is kept constant to ensure a fair test.
Case-control study A study that compares people with a disease (cases) to similar people without the disease (controls) to identify risk factors.
Randomised controlled trial (RCT) The gold standard for testing treatments, where participants are randomly assigned to treatment or control groups.
Informed consent The process by which research participants voluntarily agree to participate after understanding the risks and benefits.
Core Content
1

The Scientific Method in Disease Research

Asking and answering questions

Global Disease

Global Disease

Investigating disease follows the same scientific method used in all science:

  1. Observe and question: Notice a pattern or problem and form a specific question
  2. Research: Find out what is already known
  3. Form a hypothesis: Make a testable prediction
  4. Design and conduct an investigation: Collect data systematically
  5. Analyse and interpret: Look for patterns and relationships
  6. Draw conclusions: Determine whether the evidence supports the hypothesis
  7. Communicate: Share findings with the scientific community

In disease research, forming a good question is crucial. Questions must be:

  • Specific: "Does handwashing reduce school absenteeism?" rather than "Is hygiene important?"
  • Testable: Can be investigated through observation or experiment
  • Falsifiable: Could potentially be proven wrong
2

Study Designs

Different tools for different questions

Different research questions require different approaches:

Case-control study:

Compares people who have a disease (cases) with similar people who do not (controls) to identify risk factors.

  • Example: Compare smokers (cases) with non-smokers (controls) to see if smoking is linked to lung cancer
  • Advantage: Can study rare diseases and multiple risk factors
  • Limitation: Cannot prove causation, only association

Cohort study:

Follows a group of people over time to see who develops disease.

  • Example: Follow 10,000 people for 20 years, recording diet and exercise, to see who develops heart disease
  • Advantage: Can establish timing (which came first)
  • Limitation: Expensive and time-consuming

Randomised controlled trial (RCT):

The gold standard for testing treatments. Participants are randomly assigned to treatment or placebo (control) groups.

  • Example: Give 1,000 patients either a new drug or a placebo, without knowing which is which, and compare outcomes
  • Advantage: Randomisation eliminates bias; can prove causation
  • Limitation: Expensive; ethical constraints
3

Data Analysis and Interpretation

Making sense of numbers

Collecting data is only half the task — interpreting it correctly is equally important:

Measures of disease frequency:

  • Incidence: Number of new cases in a population over time
  • Prevalence: Total number of cases at a given time
  • Mortality rate: Deaths per population

Understanding risk:

  • Absolute risk: The actual chance of something happening (e.g., 5 in 1,000 people get disease X)
  • Relative risk: How much more likely one group is to get disease compared to another (e.g., smokers are 15x more likely to get lung cancer)

Correlation vs causation:

Just because two variables are correlated does not mean one causes the other. Ice cream sales and drowning deaths are correlated (both increase in summer), but ice cream does not cause drowning — hot weather causes both.

Establishing causation requires:

  • Temporal relationship (cause precedes effect)
  • Biological plausibility (a mechanism makes sense)
  • Consistency across studies
  • Dose-response relationship (more exposure = more effect)
4

Ethics in Disease Research

Doing good science responsibly

Medical research involves unique ethical challenges because it affects human lives:

Informed consent: Participants must voluntarily agree after understanding risks, benefits, and their right to withdraw. For children or unconscious patients, parents or guardians provide consent.

Beneficence: Research must benefit participants or society. The potential benefits must outweigh the risks.

Non-maleficence: Researchers must not harm participants. "Do no harm" is a fundamental principle.

Justice: Research benefits and burdens must be distributed fairly. Historically, vulnerable groups (prisoners, poor people, Indigenous communities) were exploited in research. Modern ethics requires equitable inclusion and protection.

Animal research: Many disease treatments are tested in animals before human trials. This raises ethical questions about animal welfare. Australian research follows the 3Rs principle: Replace animals where possible, Reduce numbers used, and Refine procedures to minimise suffering.

Research integrity: Fabricating data, plagiarising, or failing to report negative results undermines trust in science and can harm patients.

Common Misconceptions

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"A single study can prove that something causes disease." No — establishing causation requires multiple studies using different methods, consistency across populations, and biological plausibility. A single study can suggest associations but rarely proves causation.

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"If two things are correlated, one must cause the other." No — correlation does not imply causation. Many correlated variables are both caused by a third factor, or the correlation may be coincidental.

✗trong>"Research ethics slow down science and prevent important discoveries." No — ethics protect participants from harm and maintain public trust in science. Unethical research (like the Tuskegee syphilis study) caused lasting harm and distrust. Ethical research produces more reliable results.

Australian Context

Australian Research Ethics

The National Health and Medical Research Council (NHMRC): Australia's peak body for funding health and medical research and developing ethical guidelines. The NHMRC's National Statement on Ethical Conduct in Human Research sets standards for all Australian research involving humans.

Indigenous research ethics: The NHMRC has specific guidelines for research involving Aboriginal and Torres Strait Islander peoples, developed in partnership with Indigenous communities. Key principles include: community engagement, benefit to communities, cultural sensitivity, and Indigenous control over data. Researchers must demonstrate that their work will benefit the communities involved, not just advance scientific knowledge.

Clinical Trials Australia: Australia is a leading destination for clinical trials due to high-quality healthcare, rigorous ethical oversight, and diverse populations. The Therapeutic Goods Administration (TGA) regulates medicines and medical devices, ensuring safety and efficacy before approval. During COVID-19, Australian researchers conducted trials for vaccines and treatments that contributed to global pandemic response.

✍ Copy Into Your Books

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Study Types

  • Case-control: compare cases and controls
  • Cohort: follow groups over time
  • RCT: random assignment to treatment/control

Key Principles

  • Correlation ≠ causation
  • Randomisation reduces bias
  • Large samples increase reliability

Ethics

  • Informed consent
  • Beneficence and non-maleficence
  • Justice and fair distribution
  • Animal research: 3Rs
Activities
Activity 1

Design an Investigation

Apply scientific methodology.

1 A school wants to know if hand sanitiser reduces the spread of colds. Design a fair test, including hypothesis, variables, and method.
Answer in your book.
2 Explain why a randomised controlled trial is considered the "gold standard" for testing new medicines.
Answer in your book.
3 A study finds that people who drink more coffee have lower rates of heart disease. Why can we not conclude that coffee prevents heart disease?
Answer in your book.
Activity 2

Ethics Evaluation

Evaluate research ethics scenarios.

1 A company tests a new drug in a developing country where regulations are weaker than in Australia. Evaluate the ethics of this decision.
Answer in your book.
2 Why is informed consent essential in medical research? What could go wrong without it?
Answer in your book.
3 Describe how Australian research ethics guidelines protect Aboriginal and Torres Strait Islander participants.
Answer in your book.
Multiple Choice
Q

Test Your Understanding

RememberBand 3

1. What is a hypothesis?

AA proven fact
BA testable prediction
CA random guess
DA published paper
RememberBand 3

2. In a case-control study, researchers compare:

ADifferent treatments
BPeople with and without a disease
CAnimals and humans
DOld and young people
UnderstandBand 4

3. Why are randomised controlled trials considered the gold standard for testing treatments?

AThey are the cheapest
BThey eliminate bias through random assignment
CThey use the most participants
DThey take the longest
UnderstandBand 4

4. "Correlation does not imply causation" means:

AIf two variables are correlated, one definitely causes the other
BA relationship between variables does not prove one causes the other
COnly experiments can show correlation
DScientists should never study correlations
RememberBand 3

5. Which ethical principle requires that research participants voluntarily agree after understanding risks?

ABeneficence
BJustice
CInformed consent
DNon-maleficence
Short Answer
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Short Answer Questions

UnderstandBand 4

1. Describe the difference between a case-control study and a randomised controlled trial. Include one advantage and one limitation of each. 4 MARKS

Answer in your book.
UnderstandBand 4

2. Explain why "correlation does not imply causation" using a disease-related example. 4 MARKS

Answer in your book.
EvaluateBand 5

3. Evaluate the ethics of testing a new vaccine on children before it has been tested on adults. Consider both the potential benefits and the ethical concerns. 4 MARKS

Answer in your book.

Revisit Your Thinking

Go back to your Think First answer. Has your understanding changed?

Update your thinking in your book.

Answers

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MCQ 1

B — A hypothesis is a testable prediction about the relationship between variables that can be investigated through observation or experiment.

MCQ 2

B — In a case-control study, researchers compare people who have a disease (cases) with similar people who do not (controls) to identify risk factors.

MCQ 3

B — Randomised controlled trials eliminate bias by randomly assigning participants to treatment or control groups, ensuring that differences in outcomes are due to the treatment rather than other factors.

MCQ 4

B — This means that just because two variables change together does not mean one causes the other. A third factor may cause both, or the relationship may be coincidental.

MCQ 5

C — Informed consent is the process by which participants voluntarily agree to participate in research after understanding the risks, benefits, and their right to withdraw.

Short Answer 1

Model answer: A case-control study compares people who have a disease (cases) with similar people who do not (controls) to identify risk factors. Advantage: efficient for studying rare diseases and can examine multiple risk factors simultaneously. Limitation: cannot prove causation because it looks back in time; researchers cannot control exposures, and recall bias may affect results. A randomised controlled trial (RCT) randomly assigns participants to treatment or control groups and compares outcomes. Advantage: randomisation eliminates selection bias, and the control group provides a direct comparison, allowing researchers to establish causation. Limitation: expensive, time-consuming, and ethically constrained — it may be unethical to withhold effective treatments or expose participants to potential harm.

Short Answer 2

Model answer: "Correlation does not imply causation" means that just because two variables are associated does not mean one causes the other. A disease-related example: studies have found that people who consume more red wine have lower rates of heart disease. However, this does not prove red wine prevents heart disease. Red wine drinkers may have higher incomes, better diets, or more exercise — factors that independently reduce heart disease risk. The correlation may reflect these confounding variables rather than a causal effect of wine. Another example: ice cream sales and drowning deaths are correlated because both increase in summer, but ice cream does not cause drowning — hot weather causes both. In disease research, establishing causation requires controlled experiments, biological plausibility, and consistency across multiple studies.

Short Answer 3

Model answer: Testing a new vaccine on children before adult testing raises significant ethical concerns. Potential benefits: Children are vulnerable to infectious diseases and may need vaccine protection urgently. Some diseases (like rotavirus) primarily affect children, so adult testing would not provide relevant data. Early testing in children could lead to faster protection for this vulnerable group. Ethical concerns: Children cannot give fully informed consent — parents must decide on their behalf, creating a vulnerability. Children's immune systems and bodies are still developing, so side effects may differ from adults. The principle of non-maleficence requires protecting vulnerable populations from unnecessary risk. Standard practice: Most vaccine development follows a staged approach — safety testing in adults first, then gradually younger age groups. This balances the need to protect children with the ethical obligation to minimise risk. Exceptions may occur during emergencies (like COVID-19) when the disease poses greater risk to children than the vaccine. Ultimately, the decision requires careful ethical review, parental informed consent, and strong safety monitoring.

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Lesson Game

Science Sleuth

Design experiments and analyse data! Solve disease mysteries by applying scientific methodology in this investigation adventure.

Mark lesson as complete

Tick when you have finished all activities and checked your answers.

Unit 1 overview · Science subject page