LU 1 Quantitative Research Process VI (Sampling Method)

What is sampling and samples ?

• sampling : a process of selecting a sample from a population

• samples : i) a subset of a population, whose properties have been generalised to the population ii) used to estimate the characteristics of the whole population

What are the advantages and disadvantages of sampling ?

• advantages : reduce workload, save money, save time and better data quality

• disadvantages : sampling error, may create a feeling of discrimination within the population

What is sampling error ?

• a difference that occurs purely by chance between the value of a sample statistic that of the corresponding population parameter

• cannot be avoided or totally eliminated

• can be reduced by increasing sample size

What are the other sources of error in research ?

• sampling error

• poor sampling method

• questionnaire error

• behavioral effects

What are the criteria of a good sampling ?

• representative of the population

• adequate sample size

• practicality and feasibility of the sampling procedure

• economical and efficient sampling procedure

What are the type of sampling ?

• probability sampling : everyone has a known chance to be selected, preferable in most quantitative research

• non probability sampling : the chance of being selected is unknown, not preferable in quantitative research

What are the example of probability sampling ?

• simple random sampling

• systematic sampling

• cluster sampling

• multistage sampling

What are the example of non probability samping ?

• purposive

• convenient

• web panel

• snowballing

What is simple random sampling ?

• most basic, purest and easiest to understand and perform

• every sampling unit in the sampling frame has the same chance of being selected

What are the advantages & disadvantages of simple random sampling ?

• advantages : easy to understand and perform, equal chance ensures that the samples are representative

• disadvantages : large sampling frame may be impractical

What are the steps in simple random samping ?

• define the population

• create a list of all population members

• use random number generator to select participants until you reach you target sample size

What is systematic sampling ?

• interval sampling

• involves the selection of every k^th unit in the population

What are the advantages & disadvantages of systematic sampling ?

• advantages : sample is easy to select, a suitable sampling frame can be identified easily

• disadvantages : the sample may be biased, difficult to assess the precision of the estimate from one survey

What are the step to perform systematic/ interval sampling?

• know the population size, N

• determine the sample size, n

• determine the sampling interval, k

• k = N/n

What is cluster sampling ?

• a random selection of clusters

What are the advantages & disadvantages of cluster sampling ?

• advantages : cuts down the cost of preparing a sampling frame, cuts down the cost of travelling between units

• disadvantages : sampling error is higher, overestimate or underestimate sample size (unequal cluster size), might be bias

What is multistage sampling ?

• selection is done in stages until final sampling units is arrived

What are the stage of multisampling sampling ?

• 1st stage : a list of large sized sampling units is prepared (eg : town)

• 2nd stage : a list of smaller units is prepared for each selected first stage units (eg : households)

• 3rd stage : study the units

What are the advantages and disadvantages of multistage sampling ?

• advantages : cuts down cost of preparing sampling frame

• disadvantages : sampling error is increased

What is non probability sampling

• a non-random method to select samples

• potential samples have unknown chance of being selected

What are the advantages & disadvantages of non probability sampling ?

• advantages : quick and convenient, inexpensive, reduce respondent burden

• disadvantages : selection bias, difficulty in assessing the quality, non coverage bias

What is convenient sampling ?

• anyone who is willing to participate

• no criteria to be met

• little or no planning is involved

What is purposive sampling ?

• researcher rely on their judgement to select samples based on a pre-set criteria.

• sample must fit a particular profile set up by the researcher

• no random selection is used

What is snowballing sampling ?

• also known as chain referral sampling

• criteria : used in studies samples have traits that are rare to find, no official list of names of the members

• problem ; biasness, huge margin of error

What is web panel sampling ?

• a web based questionnaire panel openly accessed to people willing to respond

• often used for marketing research and pilot studies

• recruitment can be from offline channels or online channels