Business Research Methods

Sampling

“Sampling is the process of choosing sample which is a group of people, items and objects. That are taken from population for measurement and population must be representative of population so that we can generalize our findings”

What is Population? “It is an accessible group of people who meets

the eligibility criteria .”What is sample? “Subset of population selected for study.”

Concepts of sampling Target population Survey population Element Sampling unit Sampling frame Sample design

Sample size Sampling error Margin of errorConfidence levelStatistical inferenceSampling bias

Types of sampling

Probability sampling1. Simple random sampling Every person has a chance to be

included in population Complete list of everyone Sampling frame

Simple random sampling

2: systematic random technique:

Select the samples by following rules set by the researcher.

We can select members if random start or starting point is determined.

Example:Finding all kth samples.

3: stratified sampling

Stratification is the process of dividing the members into homogeneous subgroups before sampling.

Every element must be assigned to one stratum

No element must be excluded.

4: cluster samplingPopulation is divided into groups

rather than individuals.It is used for large scale survey.Make clusters and everyone in

selected clusters is sample.

5: multi stage samplingComplex form of cluster samplingDesign clusters Selecting what element within cluster

to use.

Non-probability samplingUses nonrandom procedures for selection Based on the judgment of researcherBiasedLack of objectivityNot reliableEconomical

Types of non-probability sampling1:Convenience sampling:Members are selected based on their

availability and accessibility

2: Quota sampling:Nonrandom selection of members based on the

identification of specific characteristics to increase the representativeness of sample. E.g. people aged 65 are interviewed.

3:judgmental sampling:People with specific characteristics are

selected based on the judgment and knowledge of researcher about population

Example:Want to know the opinion of drivers who got

penalty points or who are disqualified as a result of speeding issues.

Sample sizeNo of people that will be included in study.Before deciding sample size you must identify

what you will include and exclude in study.Sample size depends on:1. Type of data to be analyzed2. Desired accuracy one wishes to achieve3. No. of comparisons that will be made4. No. of variables that will be examined

Selection of sample sizePower of a test of hypothesisFor this approach researcher must be clear

that what he wants to know.For large projects we can hire the skills of

statistician.For small scale projects computer software

packages are available to determine sample size.

conclusionProbability sampling study findings that can

generalize to populationNon-probability sampling study findings that

can be generalized to the institution or place where the sample was studied.