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Transcript of Rare Populations
• "A small fraction of the general population." ^ High income households, racial or ethnic groups, people with a certain illness,
members of particular segments of the market Problems: Difficult to identify or reach
Unwilling to cooperate Gingery, Tyson. (2010, June 7). Assessing Rare Populations. Retrieved on March 20, 2013 from http://survey.cvent.com/blog/market-research-design-tips-2/accessing-rare-populations
^Sudman, Seymour; Blair, Edward. (1999). Sampling in the Twenty-First Century. Academy of Marketing Science, pp. 272-273 Examples of Characteristics ^Gingery, Tyson. (2010, June 7). Assessing Rare Populations. Retrieved on March 20, 2013 from http://survey.cvent.com/blog/market-research-design-tips-2/accessing-rare-populations
Sudman, Seymour; Blair, Edward. (1999). Sampling in the Twenty-First Century. Academy of Marketing Science, pp. 272-273 Examples mentioned in the reading: Small demographic segments
Hard-to-reach populations ^ First: See if a list already exists Screen the general population Marpsata, Maryse; Razafindratsima, Nicolas. (2010). Survey methods for hard-to-reach populations: introduction to the special issue. 5(2) 3-16 Methodological Innovations Online. Retrieved on March 21, 2013 from http://www.pbs.plym.ac.uk/mi/pdf/05-08-10/2.%20Marpsat%20and%20Razafindratsima%20English2%20(formatted).pdf Sampling Hard to Reach Populations Indirect sampling
Adaptive cluster sampling
Snowball sampling Lavallée. Pierre. (2012). Indirect Sampling for Hard-to-Reach Populations. American Statistical Association. Retrieved on March 21, 2013 from http://www.amstat.org/meetings/h2r/2012/AbstractDetails.cfm?AbstractID=301301 Indirect Sampling Lavaliee, Pierre; Caron, Pierre. ( ESTIMATION USING THE GENERALIZED WEIGHT SHARE METHOD: THE CASE OF RECORD LINKAGE. Statistics Canada, Ottawa, Ontario, KIA 0T6 CANADA. Retrieved on March 21, 2013 from http://www.amstat.org/sections/srms/proceedings/papers/1999_121.pdf
Deville, JeanClaude; Lavallée, Pierre. (2006, December) Indirect Sampling: The Foundations of the Generalized Weight Share Method. Survey Methodology. Vol. 32, No. 2, pp. 165176 Statistics Canada, Catalogue No. 12001. Retrieved on March 21, 2013 from http://publications.gc.ca.ezproxy.lib.umb.edu/Collection-R/Statcan/12-001-XIE/12-001-XIE2006002.pdf?
Xu, Xiaojian; Lavallée, Pierre. (2009, December). Treatments for link nonresponse in indirect sampling. Survey Methodology. Statistics Canada, Catalogue No. 12-001-X. Vol. 35, No. 2, pp. 153-164. Retrieved on March 21, 2013 from http://www.statcan.gc.ca/pub/12-001-x/2009002/article/11038-eng.pdf Select samples related to target population to create a sampling frame
Problem: When sample units are not linked one to one Network (or Multiplicity) Sampling Adaptive Cluster Sampling Snowball Sampling Thank You!
Step 1: "Identify one or more units in the desired population”
Step 2: Use “these units to find further units... until the sample size is met.” ^^
Sample might not represent true population
Not possible to determine sampling error
Researcher has little control
Sample bias Castillo, Joseph. (2009, April24) Snowball Sampling, Chain Referral Sampling. Explorable. Retrieved on March 21, 2013 from http://explorable.com/snowball-sampling
^Iacobucci, Dawn; Chuchhill, Gilbert A., Jr. (2010) Marketing Research, Methodological Foundations. South-Western, Cengage Learning: Mason, Ohio, p. 592
^^Laerd Research. (2012). Snowball Sampling. Lund research Ltd. Retrieved on March 21, 2013 from http://dissertation.laerd.com/snowball-sampling.php Example: Access to parents, while target population is children To solve this estimation problem, one can use the Generalized Weight Share Method (GWSM) Sampling Frame Book definition: “List of sampling units from which a sample will be drawn; the list could consist of geographical areas, institutions, individuals, or other units.” Sampling Units Book definition: “Non-overlapping collections of elements from the population.” Iacobucci, Dawn; Chuchhill, Gilbert A., Jr. (2010) Marketing Research, Methodological Foundations. South-Western, Cengage Learning: Mason, Ohio, p. 592 Terminology Nonprobability Sampling Not a random selection
May not represent population
Impossible to determine possible sampling error
Unable to make statistical inferences Laerd Research. (2012). Snowball Sampling. Lund research Ltd. Retrieved on March 21, 2013 from http://dissertation.laerd.com/snowball-sampling.php Trochim, William M.K. (2006). Nonprobability sampling. Research Methods Knowledge Base. Retrieved on March 23, 2013 from http://www.socialresearchmethods.net/kb/sampnon.php Informant directs researcher to individuals:
Outside of informant's household
Well-known by the informant Sudman, Seymour; Blair, Edward. (1999). Sampling in the Twenty-First Century. Academy of Marketing Science, pp. 272-273 Two Requirements:
1. Informant can report all network members
2. Accurately judge network size to weigh data ^Brown, J.A.; Manly B.J.F (1997, September). Restrictive adaptive cluster sampling. Department of Mathematics and Satistics, Otago University: New Zealand. Environmental and Ecological Statistics 5, 49-63 (1998). Retrieved on March 23, 2013 from http://link.springer.com.ezproxy.lib.umb.edu/article/10.1023%2FA%3A1009607403647?LI=true#page-1
^^M. Salehi, Mohammad; Seber, George A.F. (1997, September). Two-Stage Adaptive Cluster Sampling. Department of Statistics. Biometrics 53, 959-970. Auckland University: New Zealand. Retrieved on March 12, 2013 from http://www.jstor.org/stable/2533556 “The selection of sampling units at any stage of the sampling process depends on information from the units already selected." ^^ “Initial sample size is defined prior to sampling.” ^
Final sample size is unknown and inconsistent Adaptive Cluster Sampling. Retrieved on March 23, 2013 from http://www.drmehrdad.com/tasavir/adaptive.pdf Strawberry Field Example If Not, Probability Sampling Random selection
Not always practical Sampling Types If a list exists: Wiley. (1986). Journal of the Royal Statistical Society. Series A (General). Royal Statstical Society. Retrieved on March 23, 2013 from http://www.jstor.org/stable/2981886 Conclusion Pick the best sampling methods for your research needs Use it If not: Use the best methods www.prezi.com/user/HeidiM This presentation can be viewed at: