STA632 Handouts

BASIC CONCEPTS

Q . Define Sampling Techniques?

Answer: The data is very important for decision making. Appropriate method of data collection is desired. How best to obtain the data or sample. How best to use the data/sample to estimate the characteristic of the whole population. There are two parts of any sampling strategy. First is the selection procedure. Second is the estimation procedure.

Q .Define sampling?

Answer: The method of selecting the sample is called sampling design.

Q . Define sample?

Answer: A perfect sample would be a version of population, mirroring every characteristic of population. (Lohr,2nd edition).A good sample is a small but representative part of the population.

Q . What is difference between Observation and Sampling Units?

Answer: A unit that can be selected for a sample is called sampling unit. An object on which a measurement is taken is called observation unit.

Q . Define sampling frame?

Answer: The sampling frame is the list/map from which the potential sampling units are drawn. For example, List of all the class rooms , Map of area containing farms.

Q . Distinguish between parameter and statistic?

Answer: A parameter is any summary number described the whole population. A Statistic is any summary number obtained from a sample.

Sample · (Subset of class) · Statistic

Q . Define sampling error?

Answer: The errors in the estimates because sample is the part of population. The difference between the parameter and statistic is considered a sampling error. Sampling Error= Statistic-Parameter.

Q . Define non-sampling error?

Answer: These errors can occur even the whole population is studied. Non-sampling error cannot attributed to the sampling.

Q . What is selection bias?

Answer: When a random process is not considered in selection of sample. Some part of the population is ignored during selection of sample. Some results of study may not be accurate.

Q . What is measurement error?

Answer: When the response has a tendency to differ from the true value in one direction. problem with the measurement instrument.

Q . Define Nonresponse?

Answer: Ans: The individuals chosen for the sample are not ready to participate in the survey. It is called nonresponse. This is a type of selection bias.

Q . What is probability sample?

Answer: This is a sample which is obtained when each unit of the population has some chances for being included into the sample. This is obtained by a random process. Example: A bag consists on one white and one black ball.

Population · (Entire class) · Parameter · White ball · Black ball

Q . Define randomness?

Answer: When a unit has some chances of selection in the sample. When we are not certain about the selection of any unit

Q . How many types of probability sampling?

Answer: Simple random sampling, stratified sampling, cluster sampling, systematic sampling, multistage /multiphase sampling.

Q. Define Non-probability sampling?

Answer: No random process is followed for the selection of units. The population is evenly distributed with respect to the characteristics of interest.

Q . What is convenience sampling?

Answer: Respondents are selected according to convenience of researcher. This is also called accidental sampling, opportunity sampling or grab sampling.

Q. Define purposive sampling?

Answer: The units which are appropriate to meet the objective of study. The selection is based on the judgment of researcher.

Q. What is quota sampling?

Answer: The population is divided into subgroups on the basis of similar characteristics. The subgroups are called “Quota”. The nonrandom selection is made in each quota.

Q . Define snow-ball sampling?

Answer: This is also called chain sampling so it works like a chain. The selected subject asked for the assistance to reach the other subjects.

Q. Define simple random sampling?

Numberof whiteballs · P White · Numberof totalballs · P White 