Sample and sampling design (Research method)
- 1. SAMPLE &SAMPLE & SAMPLINGSAMPLING DESIGNDESIGN Department of City And Regional Planning NIAZ ALI 15CRP92 Sub: Research Method
- 2. Census: A census is the procedure of systematically acquiring and recording information about the members of a given population. It is a regularly occurring and official count of a particular population. The term is used mostly in connection with national population and housing censuses; other common censuses include agriculture, business, and traffic censuses. A survey that measures the entire target population is called a census.
- 3. What is Sample A sample is a subset of the population. It comprises some members selected from it. In other words, some, but not all, elements of the population would form the sample. According to E.R Babble “A sample is a special subset of population that is observed for purpose of making inference about the nature of the total population itself .” Example: if there are 145 in-patients in a hospital and 40 of them are to be surveyed by the hospital administrator to assess their level of satisfaction with the treatment received, then these 40 members will be the sample.
- 4. Sampling Survey The sample survey was only a small size but it did give us a window of knowledge and understanding . The sample survey that we gave to the public was given in order to determine what we needed to do. A sample survey can often change the design of a product or even the entire product as a whole, depending on current consumer opinions.
- 5. Difference between Census and sampling In Census, each and every unit of population is studied. But only few units of the population is studied in Sampling. Census refers to periodic collection of information about the populace from the entire population. However, if the next Census is far away, Sampling is the most convenient method of obtaining data about the population. Census Method demands a large amount of finance, time and labor. Relatively less amount of finance, till labor is required for sampling.
- 6. CONT……. Results obtain by the Census are quit reliable. Results obtained by the Sampling are less reliable. It is more suitable to use Census Method if population is heterogeneous in nature. and it is more suitable to use Sampling Method if population is homogeneous in nature. Samples have a margin of error though, which gets lower as the sample size increases. In other words sampling more people means obtaining better data. Instead, this type of error not present in Census as each and every part of the geographical area has to be approached for data collection .
- 8. Sample Design A sample design is the framework, or road map, that serves as the basis for the selection of a survey sample and affects many other important aspects of a survey as well. In broad context survey researchers are interested in obtaining some types of information through a survey for some population or universe. One must define a sampling frame that represents the population of interest from which a sample is to be drawn.
- 9. Following are the characteristics of good sample design: 1. Sample design should be a representative sample: A researcher selects a relatively small number for a sample from an entire population. If the sample used in an experiment is a representative sample then it will help generalize the results from a small group to large universe being studied. 2. Sample design should have marginal systematic bias: Systematic bias results from errors in the sampling procedures which cannot be reduced or eliminated by increasing the sample size. The best bet for researchers is to detect the causes and correct them. 3. Results obtained from the sample should be generalized and applicable to the whole universe: The sampling design should be created keeping in mind that samples that it covers the whole universe of the study and is not limited to a part.
- 10. Types of sample design Probability samples: Probability sampling technique is one in which every unit in the population has a chance of being selected in the sample. Non-probability samples: Non probability sampling in any sampling method where some elements of the population have no chance of selection, or where the probability of selection can’t be accurately determined. •It involves the selection of elements based on assumptions. •The selection of elements is non random.
- 12. Simple Random Sampling Design: Each element or each combination of elements has equal probability of selection. Applicable when population is small , homogeneous & readily available. A table of random number or lottery system is used to determine which are to be selected. Systematic Sampling Design: Systematic sampling relies on arranging the target population according to some ordering scheme & then selecting elements at regular intervals. Each element has equal probability of selection but combination of elements have different probabilities.
- 13. Stratified Sampling Design: Where population embraces a number of distinct categories then the population is broken down into separate groups in which each group is sampled as sub-population & a random sample is taken of each category. •Every unit in a group has same chance of being selected. •Probabilities of selection may be different for different groups.
- 14. Cluster sampling: Cluster sampling is a sampling technique used when "natural" but relatively homogeneous groupings are evident in a statistical population. •It is often used in marketing research. •In this technique, the total population is divided into these groups (or clusters) and a simple random sample of the groups is selected. Multistage sampling: Complex form of cluster sampling in which two or more levels of units are embedded one in the other. •First stage, random number of districts chosen in all states.
- 15. CONT… • Followed by random number of talukas , villages. • Then third stage units will be houses • This technique, is essentially the process of taking random samples of preceding random samples. • Multistage sampling used frequently when a complete list of all members of population not exists is appropriate.
- 16. Multiphase sampling: In multiphase sampling the different phase of observations relate to the sample units of the same type. •Part of the information collected from sample & subsample . •Survey by such procedure is less costly , less laborious & more purposeful
- 17. Non-probability samples: Convenience Sampling: Sometimes known as grab or opportunity sampling or accidental or haphazard sampling. Purposive sampling:the process whereby the researcher selects a sample based on experience or knowledge of the group to be sampled …called “purposive” sampling
- 18. Judgmental Sampling: The researcher chooses the sample based on who they think would be appropriate for the study. This is used primarily when there is a limited number of people that have expertise in the area being researched.