How we change what others think, feel, believe and do
Simple random sampling
Use in simple experiments that require a single sample to be taken from a given population or a representative sample frame.
The people in the sample frame must all be accessible and available.
Use when the target group is sufficiently large. Do not use when the target is a relatively small subgroup that might be missed by this method.
Create the sample by selecting randomly from the sample frame or population.
This can be done using a paper list of random numbers, although these days a computer is often used.
A person researching education levels within a company takes the full employee list and applies a random number algorithm to this in order to select people to interview.
The basic principle of simple random sampling is like drawing names out of a hat and is based on the mathematical property that a truly random sample (if big enough) will be representative of the target population.
The simple random sample has two key properties:
Random number generation is easy these days with a computer where, for example the Excel '=RAND()' function (just type it into any cell) generates a random number between 0 and 1. To generate a number between 0 and 5, multiply this by five and take the integer to round it down (eg. '=INT(5*RAND()').
A problem with random selection is that this is not always possible. For example to do a true random sample of the population of the USA, you would start with a list of everyone there, then select a random sample from this (very big) list, then access those people selected, no matter where they lived and whether or not they wanted to partake in the study.