Sampling Theory
Session 5 Topic: Sampling Theory/ Techniques and Discussions
Project Brief
◦ Expectations and deliverables
(Deadline October 1, 2010- EOD)
Sampling basics
◦ Fundamental Issues ◦ Errors
Sampling techniques
◦ Probabilistic ◦ Non-probabilistic
Discussions
© Krishanu Rakshit, IIM Calcutta
28 September, 2010
2
When do we use a ‘sample’ When do we use a census (population) Sampling errors
◦ Difference between a measure from sample and the measure which can be obtained from the population
Non-sampling errors
◦ Selection Error ◦ Population specification Error
A bias/error which creeps in when sample obtained through nonprobabilistic techniques does not represent the population When an inappropriate population is chosen from which a sample is selected
E.g. could be choosing a sample of cat owners for researching ‘dog food ‘
© Krishanu Rakshit, IIM Calcutta
28 September, 2010
3
Non-sampling errors
◦ Sampling frame error
A sampling frame is a directory (defining the population from which sample will be drawn) The error comes in when the sample is drawn from an inaccurate sampling frame
◦ Surrogate Information error
E.g. for studying the preference for desktops at home, the sampling frame is considered to be ‘subscription list of PC World magazine’
Often information sought is different from the information required- one of the critical errors
E.g. Classic Case of new Coke- should not have been consumers’ preferences between Old and new Coke, rather a measure of attitudinal aspects of a change in taste
© Krishanu Rakshit, IIM Calcutta
28 September, 2010
4
Non-sampling error
◦ Measurement error
Difference between information sought and information collected by the procedure (problem with Questionnaire design)
Validity issues
Experimental error
Mainly from faulty experimental design Critically, from interaction effects due to
Project Brief
◦ Expectations and deliverables
(Deadline October 1, 2010- EOD)
Sampling basics
◦ Fundamental Issues ◦ Errors
Sampling techniques
◦ Probabilistic ◦ Non-probabilistic
Discussions
© Krishanu Rakshit, IIM Calcutta
28 September, 2010
2
When do we use a ‘sample’ When do we use a census (population) Sampling errors
◦ Difference between a measure from sample and the measure which can be obtained from the population
Non-sampling errors
◦ Selection Error ◦ Population specification Error
A bias/error which creeps in when sample obtained through nonprobabilistic techniques does not represent the population When an inappropriate population is chosen from which a sample is selected
E.g. could be choosing a sample of cat owners for researching ‘dog food ‘
© Krishanu Rakshit, IIM Calcutta
28 September, 2010
3
Non-sampling errors
◦ Sampling frame error
A sampling frame is a directory (defining the population from which sample will be drawn) The error comes in when the sample is drawn from an inaccurate sampling frame
◦ Surrogate Information error
E.g. for studying the preference for desktops at home, the sampling frame is considered to be ‘subscription list of PC World magazine’
Often information sought is different from the information required- one of the critical errors
E.g. Classic Case of new Coke- should not have been consumers’ preferences between Old and new Coke, rather a measure of attitudinal aspects of a change in taste
© Krishanu Rakshit, IIM Calcutta
28 September, 2010
4
Non-sampling error
◦ Measurement error
Difference between information sought and information collected by the procedure (problem with Questionnaire design)
Validity issues
Experimental error
Mainly from faulty experimental design Critically, from interaction effects due to