This article throws light upon the top five techniques of work sampling. The techniques are: 1. Random Sampling 2. Systematic Sampling 3. Stratified Sampling 4. Cluster Sampling 5. Two-Stage Sampling.
Technique # 1. Random Sampling:
Under this plan, observations are distributed randomly over the day. There are a number of acceptable methods of achieving this. The most suitable and convenient method uses a table of random numbers. The appropriate type of table is one prepared from a rectangular distribution.
Technique # 2. Systematic Sampling:
To facilitate more productive utilization of the periods between observations, some work engineers adopt the practice of observing at regular intervals say every 15 minutes or 30 minutes or one hour. Such apian of observation schedule is called systematic sampling.
Technique # 3. Stratified Sampling:
Whenever it is known or suspected that probability of occurrence of a given state of activity is appreciably different during different periods of the study or for different portions of the population of men or machines under study, a stratified sampling plan is preferred.
Under this plan total number of observations are divided into groups such that the number of observations in a group is proportional to the fraction of the men/machines and the group represents total population of men/machines.
Technique # 4. Cluster Sampling:
When the lot submitted for the inspection consists of certain groups of clusters of items, it may be advantageous and economical to select a few clusters of items and then examine all the items in the selected clusters.
Technique # 5. Two-Stage Sampling:
When the lot submitted for the inspection consists of larger number of packages, each consisting of number of items, it may not be economical to select few packages and inspect all the items in these packages (as in case of duster sampling).
In such cases, the sample is selected in two stages. In first stage a desired number of packages (primary units) are selected at random and in the second stage, the required number of items are chosen at random from the selected primary units.
Here sampling inspection may be carried out as:
(i) Sampling by attributes, and
(ii) Sampling by variables.