Chapter 06 Populations, samples, and sample size

Populations, samples, and sample sizeChapter 6 In creating a sample --Researchers make choices:Who to collect data from?What to collect data about?How much data to collect?Population → samplePopulationall units (people or things) possessing the attributes and characteristics of interestSampling frame subset of units that have a chance to become part of the sampleSample subset of a populationResearchers study the sample to make generalizations back to the populationIdentifying the populationChoose the dimensions or characteristics meaningful to the hypothesis or research questionMust be at least one common characteristic among all members of a populationMust develop procedure to ensure representative samplingAddressing generalizabilityExtent to which conclusions developed from data collected from sample can be extended to its populationSample is representative to the degree that all units had same chance for being selectedRepresentative sampling eliminates selection bias Representativeness can only be assured through random samplingProbability samplingThe probability of any unit being included in the sample is known and equal When probability for selection is equal, selection is randomAlso known as random samplingSampling error will always occur Types of probability samplingSimple random samplingSimplest and quickestSystematic samplingIf used on a randomly ordered frame, results in truly random sampleStratified random samplingRandom sampling within all subgroupsCluster samplingRandom sampling within known clustersNonprobability samplingDoes not rely on random selectionWeakens sample-to-population representativenessUsed when other techniques will not result in an adequate or appropriate sampleUsed when researchers desire participants with special experiences or abilitiesNonprobability sampling techniquesConvenience sampleVolunteer sampleInclusion/exclusion sampleSnowball or network samplePurposive sampleQuota sampleSample sizeNumber of people/units for whom you need to collect dataDetermined prior to selecting sampleLess than the number you ask to participateThe larger the sample relative to the population, the less error or biasWith probability sampling . . .Population SizeSample Size10080200132500217100027850003575000384