A Level

# Evaluation

## 1. Evaluating methods

Produce a thorough evaluation of all sections of your investigation.

Here are some useful words when evaluating your methods.

### True value

The true value is the value that would be obtained in an ideal measurement.

### Accuracy

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.

### Precision

Precise measurements have very little spread about the mean value. A precise measurement is not necessarily accurate.

### Errors

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
• 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.

### Anomalies

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

### Be objective

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?

### Be critical

• Have you chosen the best method?
• Were you accurate and precise?

### Be ethical

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?