1 Sampling Methods in Quantitative and Qualitative Research

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<ul><li><p>*Sampling Methods in Quantitative and Qualitative Research</p></li><li><p>*Sampling</p><p>Sampling in Quantitative Research</p></li><li><p>*Sampling in Quantitative Research</p><p>PopulationThe entire aggregation of cases that meets a specified set of criteriaEligibility criteria determines the attributes of the target population</p><p>SamplingThe process of selecting a portion of the population to represent the entire population</p></li><li><p>*Sampling in Quantitative ResearchAccessible populationThe population of people available for a study</p><p>Target populationThe entire population in which the researcher is interested and to which he/she wants to generalize the results</p></li><li><p>*Sampling PlansA sample is a subset of the population</p><p>A sample should be representative and similar to the population to be studied</p></li><li><p>*Sampling PlansStrata</p><p>Subdivisions of the population based on specific characteristics</p></li><li><p>*Samples vs. the Population</p><p>More economicalMore efficientMore practical</p></li><li><p>*Problems Using SamplesSampling bias</p><p>Over-representation or under-representation of some characteristic of the population </p><p>Not representative of the population being studied</p></li><li><p>*Sampling PlansTypes of sampling plans</p><p>Nonprobability sampleConvenience samplingPurposive samplingQuota sampling</p><p>Probability sampleRandom samplingCluster samplingSystematic sampling</p></li><li><p>*Sampling PlansNonprobability sample</p><p>The selection of the sample from a population using non-random procedures</p><p>Convenience samplingPurposive samplingQuota sampling</p></li><li><p>*Sampling PlansNonprobability sample</p><p>Convenience sampling (accidental sampling)Selection of the most readily available people as participants in a studyRisk of bias and errors as sample may be atypical of the populationWeakest form of sampling</p><p>Snowball sampling (network sampling)The selection of participants by means of referrals from earlier participants</p></li><li><p>*Sampling PlansNonprobability sample</p><p>Quota samplingResearcher pre-specifies characteristics of the sample to increase its representativeness</p><p>This is used so sample includes an appropriate number of cases from each stratum (subpopulation)</p><p>Usually use age, gender, ethnicity, socioeconomic status, and medical diagnosis</p></li><li><p>*Sampling PlansNonprobability sample</p><p>Purposive sampling (judgmental sampling)Researcher selects study participants on the basis of personal judgement about which ones will be most representative or productive</p><p>Handpick cases, very subjective</p></li><li><p>*Sampling PlansNonprobability Sample Problems</p><p>Are rarely representative of the target populationBut are convenient and economical</p></li><li><p>*Sampling PlansProbability sample</p><p>The selection of the sample from a population using random procedures</p><p>Random selection each element in the population has an equal, independent chance of being selected </p><p>Should be representative of the population</p><p>Random samplingCluster samplingSystematic sampling</p></li><li><p>*Sampling PlansProbability sample</p><p>Simple Random sampling</p><p> Listing the population elements Elements are assigned a number Table of random numbers is used to draw at random a sample</p></li><li><p>*Sampling PlansProbability sample</p><p>Stratified Random sampling</p><p> Population divided into homogenous subsets Elements are selected at random Increases representativeness of the final sample</p></li><li><p>*Sampling PlansProbability sample</p><p>Stratified Random sampling</p><p>Proportionate sample a sample that results when the researcher samples from different strata of a population in direct proportion to their representation in the population</p></li><li><p>*Sampling PlansProbability sample</p><p>Stratified Random sampling</p><p>Disproportionate sample a sample that results when the researcher samples differing proportions of study participants from different strata that are comparatively smaller</p><p>Used when comparison between strata of unequal membership size are desired</p></li><li><p>*Sampling PlansProbability sample</p><p>Cluster sampling (multistage sampling)</p><p>A form of sampling in which large groupings are selected first, with successive subsampling of smaller units</p><p>Used for large scale sampling where it is impossible to have a listing of all elements</p></li><li><p>*Sampling PlansProbability sample</p><p>Systematic sampling </p><p>The selection of study participants such that every Xth person or element in a sampling frame or list is chosen</p><p>Population is divided by the size of desired sample to obtain a sampling interval</p><p>Sampling interval is the standard distance between the selected elements</p></li><li><p>*Sampling PlansSample Size (Quantitative Studies)</p><p>Sample size</p><p>The number of participants in a sample</p><p>Use the largest sample possible</p><p>The larger the sample, the more representative it is likely to be</p><p>The larger the sample, the smaller the sampling error</p><p>Large samples counter balance atypical values</p></li><li><p>*Critiquing the Sampling PlanDid the researcher adequately describe the sampling planType of sampling usedThe population under studyNumber of participantsMain characteristics of participantsNumber and characteristics of potential subjects</p><p>Were good sampling decisions made</p><p>Was the sample representative of the population</p></li><li><p>*Critiquing the Sampling PlanResponse ratesThe number of people participating in a study relative to the number of people sampled</p><p>Nonresponse biasDifferences between participants and those who declined to participateA bias that can result when a nonrandom subset of people invited to participate in a study fail to do so</p></li><li><p>*Sampling in Qualitative Studies</p></li><li><p>*Sampling in Qualitative StudiesUses small samplesNon-random samplesSample design is emergent</p></li><li><p>*Sampling in Qualitative StudiesTypes of Qualitative Sampling</p><p>Convenience sampling (volunteer sample)Snowball samplingPurposive sampling (theoretical sampling, purposeful sampling)Researcher selects sample based on information needs which emerged from earlier findings</p></li><li><p>*Sampling in Qualitative StudiesSample SizeSample size is based on informational needsData saturation is soughtSampling to the point at which no new information is obtained and redundancy is achieved</p></li><li><p>*Sampling in Qualitative StudiesEvaluating Sampling Plans Based on:AdequacySufficiency and quality of the data the sample yielded</p><p>AppropriatenessUsing the best informants for the sample, those who will provide the best information</p></li><li><p>*Reference</p><p>Loiselle, C. G., Profetto-McGrath, J., Polit, D. F., &amp; Beck, C. T. (2011). Canadian essentials of nursing research. (Third Edition). Philadelphia: Lippincott, Williams &amp; Wilkins. </p><p>******************************</p></li></ul>