Non-random sampling

Also called: Non-probability sampling · Topic: Economic Data: Census, NSS, Surveys and Statistical Tools · NCERT: Class 11, Ch 2 "Collection of Data"

Meaning

In non-random sampling, units do not all have an equal chance of selection. The investigator picks them by judgement, purpose, convenience or quota (a fixed number from each group). It is quick and easy, but personal bias creeps in, so the sample may not represent the population. Results from such a sample are therefore less reliable for the whole population.

Example

NCERT's example: out of 100 households, a researcher picks 10 that are nearby or known to them. The households left out may be quite different, so the findings can be biased.

Don't confuse with

• Random sampling: every unit has an equal chance of selection. "Random" does not mean haphazard. It means chance decides, for example through the lottery method.

Related concepts

• Census
• Sample survey
• Population
• Sample
• Representative sample
• Population parameter
• Random sampling
• Sampling frame
• Lottery method
• Random number table

Read more

• Census or sample: populations, samples and sampling methods