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# Data collection

The type of data collected and how the associated sampling takes place depend on the statistical question asked.

There are a number of aspects of data collection that need to be considered when carrying out a statistical investigation.

• Choose the questions (e.g. "Do you like …?", "How tall is …?") that will determine the type of data collected (e.g. categorical, numerical).
• Choose a sample size that will allow confidence in the conclusion.
Use repeated sampling to demonstrate how much variation occurs in samples of different sizes.
• Avoid bias in data collection.
Explore sources of bias in various contexts where data are collected.
• Understand the importance of random selection.
Explore various methods of random sampling.
• Know the relationship between samples and populations.
Learn to define populations and samples in various statistical contexts.

## Types of data

The type of data collected depends on the type of question that is asked.

## Sample size and variation

Generally speaking, as the sample size increases the information from the data becomes more reliable.

## Bias in data

Bias in data can distort all results gained from statistical investigation.

## Samples and populations

It is important to make a distinction between the population, sample and a case.