690+sampling

sampling

From Fraenkel/Wallen ch. 6

sample a fairly small number of individual members sometimes these represent how a larger group might act or believe, but depend on how representative or similar they are

sampling: process of selecting individuals

larger groups to apply results is the population

difficult to study an entire population, so that's why they study samples

selecting a sample (steps): 1. define the population of interest: more narrow=save time, detailed so others can apply results

target population: the actual population which resarchaer would like to generalize

accessible population: resercher is able to generalize about

random sampling: random, equal chance of selection, drawings 3 types/methods: 1. simple random sampling: equal and indept chance of selection table of random numbers, extremely large list of # with no order or pattern 2. stratified random sampling: certain subgroups or strata are selected in same proportion in population 3. cluster sampling: selection of groups or clusters rather than individuals, like simple random, but clusters are selected not individuals two-stage random sampling: select 25 classes from 300 total, then from there select 4 students per class

nonrandom sampling: purposive sampling, no chance, methods: systematic sampling: every nth individual of a population is selected 2 terms: sampling interval= population size/desired sample size sampling ratio= sample size/population size

snowball sampling: (purposive sampling) pick a sample and they suggest other people, or they know more qualitative, as needed, no randomization

periodicity: if some pattern accidently coincides with sampling interval

convenience sampling: group of individuals conveniently available for study, avoided if possible, not representative of any population

purposive sampling: personal judgement to select a sample, different than convenience bc researchers do not simply study whoever is avaialbe but use their judgement to selelct sample they bleieve will provide data they'll need.

how big of a sample? as big as the researcher can get without too much time and energy

suggestions for size descriptive: min. would be 100 correlational: 50 experimental causal-coparative: 30

from Marcie's slides (wk 3)...



From Fraenkel/Wallen website
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__Samples and Sampling__ __Samples and Populations__ __Random Versus Nonrandom Sampling__ __Random Sampling Methods__ __Nonrandom Sampling Methods__ __Sample Size__
 * The term "sampling," as used in research, refers to the process of selecting the individuals who will participate (e.g., be observed or questioned) in a research study.
 * A sample is any part of a population of individuals on whom information is obtained. It may, for a variety of reasons, be different from the sample originally selected.
 * The term "population," as used in research, refers to all the members of a particular group. It is the group of interest to the researcher, the group to whom the researcher would like to generalize the results of a study.
 * A target population is the actual population to whom the researcher would like to generalize; the accessible population is the population to whom the researcher is entitled to generalize.
 * A representative sample is a sample that is similar to the population on all characteristics.
 * Sampling may be either random or nonrandom. Random sampling methods include simple random sampling, stratified random sampling, and cluster random sampling. Nonrandom sampling methods include systematic sampling, convenience sampling, and purposive sampling.
 * A simple random sample is a sample selected from a population in such a manner that all members of the population have an equal chance of being selected.
 * A stratified random sample is a sample selected so that certain characteristics are represented in the sample in the same proportion as they occur in the population.
 * A cluster random sample is one obtained by using groups as the sampling unit rather than individuals.
 * A two-stage random sample selects groups randomly and then chooses individuals randomly from these groups.
 * A table of random numbers is a table of numbers, listed and arranged in no particular order, that is used to select a random sample.
 * A systematic sample is a sample obtained by selecting every //n//th name in a population.
 * A convenience sample is any group of individuals that is conveniently available to be studied.
 * A purposive sample is a sample selected because the individuals have special qualifications of some sort, or because of prior evidence of representativeness.
 * Samples should be as large as a researcher can obtain with a reasonable expenditure of time and energy. A recommended minimum number of subjects is 100 for a descriptive study, 50 for a correlational study, and 30 in each group for experimental and causal-comparative studies.