Sampling Business Research Methods

2. Sampling Business Research Methods 2

3. Sampling • Sampling: The process of selecting a sufficient number of elements from the population, so that results from analyzing the sample are generalizable to the population. OR • The basic idea of sampling is that by selecting some of the elements in population, we draw conclusions about the entire population.

4. Populationrefers to the totality of people, events, things of interest or objects (which may be individuals, households, organizations, countries etc.) that the researcher wishes to investigate. E.g. All office workers in the firm compose a population of interest; all 4,000 files define a population of interest. • An elementis a single member of the population. • Element is the unit of study; it may be a person or may be something else. • E.g.: Each staff member questioned about an optimal promotional strategy is a population element. • Each advertising account analyzed is an element of an account population • Each ad is an element of a population of advertisements

5. Census • A census is a count of all the elements in a population; • If 4,000 files define the population, a census would obtain information from every one of them. • Sample: A subset of the population selected to investigate the properties of the population. Because populations are often extremely large, or even infinite, it is usually impossible – for cost and practical reasons – to take measurements on every element of the population. For this reason, more often, we draw a sample and generalize from the properties of the sample to the broader population. • Sampling unit:The element or set of elements that is available for selection in some stage of the sampling process. • A subject is a single member of the sample, just as an element is a single member of the population.

6. What is a Good Sample? • Sampling is acceptable only when it adequately reflects the population from which it is drawn; • No sample is a perfect representation of its population • The ultimate test of a sample design is how well it represents the characteristics of the population it purports to represents. • In measurement terms, the sample must be valid. • Validity of a sample depends on two considerations: • Accuracy and • Precision

7. Questions • You wish to study the care arrangements of at government hospitals in Islamabad and Rwp. • Find out the opinions of workers in a factory on changed working arrangements • Measuring students’ satisfaction level about teaching in the MBA/BBA/BS/MS programs • Find out the changing attitude of Pakistanis towards immigration to Australia, NZ, USA, UK.

8. Advantages of Sampling • Sometimes there is a need for sampling. Suppose we want to inspect the eggs, the bullets, the missiles and the tires of some firm. The study may be such that the objects are destroyed during the process of inspection. Sampling plays a key role in this process. • Sampling saves money as it is much cheaper to collect the desired information from a small sample than from the whole population. • Sampling saves a lot of time and energy as the needed data are collected and processed much faster than census information.  • Sampling makes it possible to obtain more detailed information from each unit of the sample as collecting data from a few units of the population. • Sampling has much smaller “non-response”, following up of which is much easier. • The most important advantage of sampling is that it provides a valid measure of reliability for the sample estimates. • Sample data is also used to check the accuracy of the census data.   

9. The Sampling Process • Major steps in sampling: • Define the population (elements, geographic boundaries, and time) • Determine the sample frame • Determine the sampling design • Determine the appropriate sample size • Execute the sampling process

10. Steps in sampling process • The population is defined in terms of element, units, time, etc. • Sampling unit: Maybe on a geographical basis such as state, province, district, village, etc. • Sampling frame: To prepare the source list to cover all the samples in the sampling frame that is as true a representative of the population as possible. • Size of the sample: Number of items to be selected from the universe to constitute a sample. Sampling Techniques • Probability versus nonprobability sampling • Probability sampling: elements in the population have a known and non-zero chance of being chosen

11. Sampling Techniques • Probability Sampling • Simple Random Sampling • Systematic Sampling • Stratified Random Sampling • Cluster Sampling • Nonprobability Sampling • Convenience Sampling • Judgment Sampling • Quota Sampling

12. Simple Random Sampling • Procedure • Each element has a known and equal chance of being selected • Characteristics • Highly generalizable • Easily understood • Reliable population frame necessary

13. Simple random sampling (all members have equal chance of being selected)

14. Systematic Sampling • Procedure • Each nth element, starting with random choice of an element between 1 and n • Characteristics • Easier than simple random sampling • Systematic biases when elements are not randomly listed

15. Systematic sampling (systematic sampling involves selecting every nth case within a defined population)

16. Cluster Sampling • Procedure • Divide of population in clusters • Random selection of clusters • Include all elements from selected clusters • Characteristics • Intercluster homogeneity • Intracluster heterogeneity • Easy and cost efficient • Low correspondence with reality

17. Cluster sampling (cluster sampling involves surveying whole clusters of the population selected through a defined random sampling strategy.)

18. Stratified Sampling • Procedure • Divide of population in strata • Include all strata • Random selection of elements from strata • Proportionate • Disproportionate • Characteristics • Interstrata heterogeneity • Intrastratum homogeneity • Includes all relevant subpopulations

19. Example

20. Stratified random sampling(Dividing your population into various subgroups and then taking a simple random sample within each.)

21. Thanks to Allah