Research Methodology

Lecture No :14

(Sampling Design)

Recap

• Data collection Interviews and Questionnaires• Personally Administered Questionnaires• Mail questionnaires• Guide line for wordings

– Content and purpose (Subjective vs Objective)– Language and wording ( slang/technical)– Types of formats (open / closed ended)– Positively worded and Negatively worded– Bias/ Favoritism(Leading, loaded, ambiguous, double barrel,

socially desirable)

• Length of the question• Funneling

Lecture Objectives

•Define sampling, reasons for sampling, sample, population, element, sampling unit and subject•Sampling process•Different sampling design

Sampling

The process of selecting the right individuals, objects, or events as representative of entire population is known as sampling.

PopulationPopulation

SampleSample

Relationship between sample and population

Reasons for Sampling

• Budget and time Constraints (in case of large populations)

• High degree of accuracy and reliability (if sample is representative of population)

• Sampling may sometimes produce more accurate results than taking a census as in the latter, there are more risks for making interviewer and other errors due to the high volume of persons contacted and the number of census takers, some of whom may not be well-trained

Population

It refers to the entire group of people, events or things of interest that the researcher wishes to investigate.

Example: If regulators want to know how patients in nursing homes run by a company in France are cared for, then all the patients in all the nursing homes run by them will from the population.

Element

An element is a single member of a population

Example: If 1000 blue collar workers(labor workers) in a particular organization happen to be the population of interest to a researcher, each blue collar worker therein is an element.

Sample

A sample is a subset or subgroup of the population. By studying the sample, the researcher should be able to draw conclusions that are generalizable to the population of interest.

Example: If there are 145 in-patients in a hospital and 40 of them are to be surveyed by the hospital administrator to access their level of satisfaction with the treatment received, then these 40 members will be the sample.

Sampling unit

It is the element or set of elements that is available for selection in some stage of sampling process.

Example: Sampling units in a multistage sample are city blocks, households, and individuals within the households.

Subject

It is a single member of the sample, just as an element is a single member of the population.

Example: If a sample of 50 machines from a total of 500 machines is to inspected, then everyone of the 50 machines is a subject, just as every single machine in the population of total population of 500 machines is an element

Parameters

The characteristics of the population such as the population mean, the population standard deviation, and the population variance are referred to as its parameters.

Example: Average weight, µ, of all 30 year old women in Australia, % of voters, p, in N.S.W who think the Government is doing a good job to control inflation.

The Sampling Process

Sampling is the process of selecting a sufficient number of right elements from the population so, the major steps in the sampling include.

1.Defining the population

2.Determine the sample process

3.Determine the sampling design

4.Determine the appropriate sample size

5.Execute the sampling process

The Sampling Process

Defining the populationSampling begins with precisely defining the target population. The target population must be defined in terms of elements, geographical boundaries and time.

Example: A target population may be, for example, all faculty members in the Department of Management Sciences in the V-COMSATS network,

All housewives in Islamabad,

All pre-college students in Rawalpindi,

• The target group should be clearly defined if possible, for example, do all pre-college students include only primary and secondary students or also students in other specialized educational institutions?

Determining the sample frameThe sampling frame is a (physical) representation of all the elements in the population from which he sample is drawn. Also termed as a List.

•Often, the list does not include the entire population. The discrepancy is often a source of error associated with the selection of the sample (sampling frame error)

•Information relating to sampling frames can be obtained from commercial organizations

Example: Student telephone directory (for the student population), the list of companies on the stock exchange, the directory of medical doctors and specialists, the yellow pages (for businesses)

Determining the sample design

Two major types of sampling•Probability sampling

The elements in the population have some known, non zero chances or probability of being selected as sample subjects.•Non probability sampling

The elements do not have a known or predetermined chance of being selected as subjects.

Factors affecting sampling design

• The relevant target population of focus to the study

• The parameters we are interested in investigating

• The kind of sample frame is available

• Costs and Time are attached to the sample design and collection of Data

Determining the sample size

The decision about the how large the sample size should be can be very difficult one. These factors affecting the sampling decision are•The research objective•The extent of precision desired(the confidence interval)•The acceptance risk in predicting that level of precision(confidence level)•The amount of variability in the population itself•The cost and time constraints•In some cases, the size of population itself

Executing the sample process

In this final stage of sampling process, decision with respect to the

the target population,

the sampling frame,

the sample technique, and

the sample size have to be implemented.

• Example:

• A young researcher was investigating the antecedents of salesperson performance.

• To examine his hypotheses, data were collected from the chief sales executive in the Pakistan (the target population) via mail questionnaire.

• The sample was initially drawn from the published business register (the sampling frame), but supplemented with respondent recommendations and other additions, in a judgment sampling methodology.

• The questionnaires were subsequently distributed to sales executives of 450 companies (the sample size).

Non response and non response errors

• A failure to obtain information from a number of subjects included in the sample

• Those who do respond to your survey are different from those who did not on (one of the) characteristics of interest in your study

• Two important sources of non response errors are not at homes and refusals

Reducing the rate of refusals

• The rate of refusals depends, among other things, on the length of the survey, the data collection method and the backing of research.

• Decrease in survey length, personal interviews/questionnaire instead of mail questionnaire and the sponsorship of the research often improve the overall return rate.

Recap

• Sampling is the process of selecting the right individuals

• Sample is used to represent the whole data or population

• Sampling process include defining population, sample frame, sampling design, sample size and sampling process