Designing Studies into the Effects of Risk Factors (Edexcel International AS Biology): Revision Note
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
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