# MKT 500 Chapter Notes - Chapter 9: Simple Random Sample, Sample Size Determination, Sampling Error

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Lecture on: September 18, 2012

**explore XL Data Analyst

Basic concepts in samples and sampling

- Population: entire group under study as specified by the research project

- Sample: subset of the population that would represent the entire group

- Census: defined as an accounting of everyone in the population

- Sampling error:

o The method of sample selection

o The size of the sample

- Sample frame: master list of all members of the population

Determining size of a sample

- How to calculate sample size – page 296 for formula

- Sample size adjustment formula:

o Adjusted sample size = calculated sample size * (1/incidence rate %) * (1/response

rate %)

- Sometimes sample size must be adjusted because of time pressure, cost constraint, study

objectives, and data analysis procedures

How to select a representative sample

- Probability sampling:

o Simple random sampling: random digit dialling, table of random numbers, etc.

Probability of selection = sample size/population size

o Systematic sampling: “skip interval” – every third person for example

Skip interval = population list size/sample size

o Cluster sampling: population is divided in similar groups – researcher can select few

clusters or draw samples from each cluster

Area sampling: researcher divides the population to be surveyed into

geographic areas such as census tracts, cities, neighborhoods etc.

One-step area sampling: researcher may believe the various geographic

areas to be sufficiently identical to permit them to concentrate on one area

and then generalize the results to the full population

Two-step area sampling: choose random sample of areas, and then decide on

a probability method to sample individuals within the chosen areas

o Stratified sampling: if the population is believed to have a skewed distribution for

one of more of its distinguishing factors, the researcher identifies subpopulations

called strata. A random sample if taken from each stratum.

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