sp 225 lecture 2
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SP 225 Lecture 2. Writing with Statistics Sampling Methods. Agenda. Survey Sampling Sampling basics United States Census Census Issue Essay. Designing Studies. Selection Method Questionnaire Design United States Census. Population vs. Sample. - PowerPoint PPT PresentationTRANSCRIPT
SP 225Lecture 2
Writing with StatisticsSampling Methods
Agenda Survey Sampling
Sampling basics United States Census
Census Issue Essay
Designing Studies
Selection Method Questionnaire Design United States Census
Population vs. Sample
Population: All subjects in a study population
Sample: Subset of subjects included in the study
Parameter vs. Statistic
Population: All PeopleParameter: 5 of 15 or 33% wear glasses
Sample: 3 Randomly Selected People
Statistic: 0 of 3 or 0% wear glasses
Random Sampling
Random sample: each individual member of a population has an equal chance of being selected
EPSEM Important Questions:
Is every member of a population equally likely to be chosen?
Is every combination of members equally likely to be chosen?
Convenience Sampling
uses results that are easy to get
Systematic Sampling
Select some starting point and then select every k th element in the population
Stratified Sampling
subdivide the population into at least two different subgroups that share the same characteristics,
then draw a sample from each subgroup (or stratum)
Cluster Samplingdivide the population into sections
(or clusters); randomly select some of those clusters; choose all members from selected clusters
Sampling Error
Sample Error: Difference between sample result and true population result
Non-Sample Error: Difference caused by data that has been incorrectly collected, recorded or analyzed
Common Study Problems
Loaded questions Would you vote for Mr. President if you knew
he had gone to prison? (push-polling) Order of questions
Would you say traffic contributes more to air pollution than industry? (45% traffic, 27% ind.)
Would you say industry contributes more to pollution than traffic? (24% traffic, 57% ind.)
The United States Census
Every 10 Years the Census Bureau attempts to count and survey all citizens of the United States
Number of US Representatives in each state are determined by the census
The amount of Federal funds each state receives depends on the Census (over $185 billion each year)
Approximately 310 million residents Requires 860,000 employees to conduct the census All households receive a short-form questionnaire
and 1 in 6 receive a long-form questionnaire that takes about 40 minutes to complete
Census Methodology
The census is used to calculate population parameters
Is the census successful?
Differential Undercount Some groups counted at different rates The General Accounting Office estimates some
states were entitled to and additional $208 million while some states were overpaid $368 million
In 1980 a House district was taken from Indiana and given to Florida after count correction
Legal challenges against imputation and to require the use of sampling to correct counts
http://www.gao.gov/new.items/d09832t.pdf http://www.census.gov/srd/papers/pdf/rrs2005-01.pdf
Census Correction
http://2010.census.gov/2010census/ Count Question Resolution petition for
local governments
Statistical Methods for Correction 1850 counts for California counties lost at sea 1940 sampling was used to determine personal
characteristics so less households were required to use the long form
Imputation used alone or with sampling 1970 used to correct count when the post office
had only partial updated address listings Sampling estimates number missed Imputation determines characteristics
1980 Census tries synthetic estimation 1990 sampling used for those on probation with
help of probation officers
Sampling in the 2000 Census
Sampling for non response Sample non responders in each census
tract (1700 households) to test rate of vacancy
Capture-recapture for large geographic areas
Multiplicity estimation for homeless combines count with usage
Census Discussion What groups of people are more likely to be
missed by the census?What does the term differential undercount mean?
How are census results confirmed? How has sampling historically been used in the
census? What arguments are there in favor of sampling
in the census? What arguments are there against sampling in
the census?
Census Essay Write a position paper arguing either the
Democratic or Republican position on the use of sampling methods considered during the 2000 Census to arrive at an adjusted count in the 2010 Census
In your essay: Clearly state and justify the position Explain usage, operation and scope of
sampling methods under consideration Enumerate the consequences of your position Address the counter position
Reading
Chapter 1 of Essentials of Social Research