The Scientific Method & Evidence (DP IB Theory of Knowledge): Revision Note

The scientific method & evidence

• Scientific knowledge is justified using experimental evidence to support an explanation of an observed pattern

• Confidence in scientific claims increases when studies are well-designed, results can be replicated, and findings survive critical review

• Scientific knowledge isn't produced by observation alone; imagination is needed to form hypotheses and design experiments, and reasoning is needed to interpret evidence and build theories

Observation and experimentation

• Observation is noticing a pattern or process in the natural world that raises a scientific question

  • E.g. noticing that plants growing near a window bend towards the light, which raises the question of whether light affects the direction of plant growth

• Experimentation is a planned test designed to answer that question

  • During an experiment, one variable is deliberately changed (the independent variable), and the outcome is measured (the dependent variable)

  • Other relevant factors are kept constant, or controlled, so differences in results can be more confidently attributed to the variable being tested

• Evidence comes from the recorded results of the experiment, alongside details of the method that allow other scientists to judge reliability and carry out repeats

Hypothesis testing

• A hypothesis is a testable statement about what will happen under certain conditions

• Testing a hypothesis involves collecting data that could support it or count against it

• Support for a hypothesis increases confidence, but does not give absolute proof

  • Confidence grows when results are consistent across repeats and different methods

Falsifiability

• A claim is falsifiable if there is a possible observation or result that would show it is false

  • Falsifiability matters because it sets a clear standard for relevant counter-evidence

  • If nothing could count against a claim, it cannot be properly tested as scientific knowledge

• Note that some scientific claims are about likelihood rather than certainty, so they predict a pattern in the results instead of one fixed outcome every time

  • E.g. a medicine may be expected to lower blood pressure in most patients, even though a few may not respond, so evidence is judged by the overall trend and how big the effect is

Peer review and replication

• Peer review and replication are key methods used to evaluate scientific work and strengthen the justification of its claims

• Peer review is evaluation by other experts to judge whether methods and conclusions are justified before publication

  • Note that peer review can reduce error, but it does not guarantee that a claim is true

• Replication is repeating a study to see if similar results occur under the same conditions

  • This strengthens justification because it reduces the chance of a one-off error or chance result

  • Failed replication can reveal hidden variables, weak methods or overstated conclusions

Tools 

• Scientific tools are the instruments, technologies and techniques scientists use to observe, measure and analyse the natural world

  • Physical instruments include microscopes, telescopes and thermometers

  • Conceptual tools include mathematics, statistical methods and computational models

• Scientific tools help us overcome the limits of human observation

• The development of scientific tools has and will continue to result in shifts in what we know in the sciences

• Scientific tools can provide the evidence needed to test hypotheses and support justified conclusions