Edexcel International A Level Biology

Revision Notes

1.16 Designing Studies into the Effects of Risk Factors

Test Yourself

Features of a Good Study on Illness

  • There are a number of factors to consider when evaluating the design of a study
    • The sample of people included in the study
      • Sample size should be representative of the population involved; larger samples are more likely to be representative
      • Randomly selecting participants removes bias and increases the likelihood of a representative sample
        • Selecting people from among friends or from among people at a gym, for example, is likely to select people who have similar lifestyles; this would be a biased sample
    • Control variables; the more variables that have been controlled, the more reliable and valid the data
      • Reliable data can be reproduced by repeating an experiment
      • Valid data has only tested one independent variable whilst all other variables are controlled
    • Avoiding bias; there should be no bias involved in the collection or analysis of data
      • Bias in data can come from human sources, e.g. by selecting a non-random sample or manipulating data to emphasise a certain outcome
      • Bias can be a problem when, e.g. scientists are employed by a company that desires a particular result, or when scientific funding is dependent on specific outcomes
    • Controls; the use of an experimental control provides a point of comparison and ensures that the results are due to the variable of interest
      • An experimental control condition in a study should be the same as every other condition except that the independent variable should be absent, e.g. in a drug trial the control group would be identical to the group receiving the trial drug, except that they would be given a sugar pill instead of the drug; this is known as a placebo
    • Repetition; repeats of the data need to be taken within a study, and similar results should be collected
      • Similar results are reliable 
    • Reproducible; it should be possible to reproduce a set of findings by repeating an entire investigation
      • This is why scientists always write up the method used in a study

You've read 0 of your 0 free revision notes

Get unlimited access

to absolutely everything:

  • Downloadable PDFs
  • Unlimited Revision Notes
  • Topic Questions
  • Past Papers
  • Model Answers
  • Videos (Maths and Science)

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Naomi H

Author: Naomi H

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.