Chapter 2 – Sampling Methods

Population

An aggregate of items to be studied for an investigation. Population may be finite or infinite. Finite population means limited no. of items say 14 banks, 100 branches. Infinite population means unlimited items bank customers, bank borrowers etc.

Sample

Part of the population (or universe) which is selected for the purpose of investigation. The technique of statistical investigation based on sample data is called sample method.

Census and sampling

In census, the information is obtained from all items but in sampling it is done from limited items. Census is suitable where the area of investigation is relatively small. There is greater degree of accuracy in census. On the other hand its cost is very high and cost of sampling is smaller. Verification of information collected under sampling is possible.

Statistics

It is a measure that describes the characteristics of a sample.

Parameter 

It is the value that describes the characteristic of a population

Random Sampling

  1. Simple Random Sampling
  • Each item in entire population to have an equal chance of being included in the sample
  • Sample without replacement Ex.- If required to select 2 students(Samples) from 10 students, first select 1 student and side it and select second student from remain 9 students
  • Sample with replacement Ex.- If required to select 2 students(Samples) from 10 students, first select 1 student and note name of student and again select second student from all these 10 students. There is a chance to select same student again.
  1. Systematic Sampling
  • Elements are selected from the population at a uniform level that is measured in time, order or space
  1. Stratified Sampling
  • Divide population into relatively homogeneous group called strata
  • Ex-age, sex, upper-middle-lower class etc.
  • Each group has small variation within itself but there is wide variation between group
  1. Cluster Sampling
  • Divide the population into group or clusters and then select a random sample of these clusters
  • Considerable variation within each group but the groups are essentially similar to each other

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