## Simple Random Sampling

Sampling involves observing or testingpart of the population. The accuracy of of any results increaseswith the sample size, so a set level of accuracy requires a certainsample size.

For a simple random sample, everymember of the population must have an equal chance of being sampled.Random sampling can be carried out using random number tables. Totake a sample of size n from a population of size N, give eachmember of the population a number from 1 to N and use ranfom numbertables to select the sample, ignoring any random number which doesnot correspond to a member of the popluation. If the population is100 but the sample size is 60, use only the numbers 00 – 59 in thetables and ignore the numbers 60 – 99, and any second occurrenceof the same number until the sample is chosen.

Advantages

1. selection is truly random and freefrom bias

2. the method is easy to use

3. the probability of each memberbeing selected is known and equal to n over N .

Disadvantages

1. it is not suitable when the samplesize is large.

2. it is not always possible to obtaindate from a chosen member

3. the sample is limited in accuracybecause the whole population is not sampled

There is an equivalent method, calledlottery sampling, which involves each member having their namewritten on a piece of paper which is then drawn from a hat.