1. Evaluating methods
Produce a thorough evaluation of all sections of your investigation.
Here are some useful words when evaluating your methods.
The true value is the value that would be obtained in an ideal measurement.
Accuracy means how close a measurement is to the true value.
The closer a measured value is to the true value, the more accurate it is. The further a measured value is from the true value, the greater the error.
Precise measurements have very little spread about the mean value. A precise measurement is not necessarily accurate.
An error is the difference between the result that you found and the true value.
There are three possible sources of error:
- Measurement error: mistakes made when collecting the data, such as a student
mis-reading a thermometer.
- Operator error: differences in the results collected by different people, such as different people giving different scores.
- Sampling error: local differences meaning that one sample gives slightly different results to another.
These can produce two possible types of error:
Random error: these cause results to be spread about the true value. For example, imagine a student takes 20 temperature readings and mis-reads the thermometer for 2 of the readings. The effect of random errors can be reduced by taking more measurements.
Systematic error: these cause results to differ from the true value by a consistent amount each time the measurement is made. For example, imagine a student uses weighing scales which have not been zeroed, so all the results are 10g too high. The effect of systematic errors cannot be reduced by taking more measurements.
These are values in a set of results which are judged not to be part of the variation caused by random uncertainty.
Questions to consider
Think about the frequency and timing of observations.
- Have you taken enough samples to be representative?
- How did you avoid bias?
- For non-probability sampling, what are the limitations?
- Did interviewees understand the questions?
- How did you deal with non-responders?
- Have you chosen the best method?
- Were you accurate and precise?
The best geographical investigations will consider the ethical implications at each stage.
- How did you avoid damaging the environment?
- How did you avoid causing offence or a nuisance?
- Did you have consent to carry out observations?