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26 Cards in this Set
- Front
- Back
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What is the Sampling Design Process? |
Define population, Determine Sampling Frame, Determine Sampling Procedure (probability or non-probability), Determine appropriate sample size and then Execute sampling design |
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What is Probability Sampling? What are the 4 types? |
Equal Chance of being included in the sample (random) Simple random sampling Systematic sampling Stratified Sampling Cluster Sampling |
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What is non-probability sampling? What are the 4 types? |
unequal chance to be included in the sample (non-random) Convenience Judgement Snowball Quota |
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Probability Sampling: An objective procedure in which the probability ofselection is ? and is known ? foreach population unit. |
nonzero and known in advance |
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How does Simple Random Sampling work? |
population members are selected directly from a sampling frame, equal probability of selection for every member uses a random number table or random number generator |
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what is systematic sampling? |
order all units in the sampling frame based on some variable and number them from 1 to N Choose a random starting place from 1 to N and then sample every K units after that |
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What is Stratified Sampling? |
The chosen sample is forced to contain units from each of the segments or strata of the population -equalizing important variables (year in school, product use, geographic area, etc) Steps: pop. is divided into mutually exclusive and exhaustive strata based on appropriate population characteristics, SRS then drawn from each stratum |
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What is Cluster Sampling? |
Clusters of population units are selected at random and then all or some randomly chosen units in the selected clusters are studied steps: population is divided into mutually exclusive/exhaustive subgroups/clusters, SRS of a few clusters selected, all or some randomly chosen units in the selected clusters are studied |
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Non-Probability Sampling: Subjective procedure in which the probability ofselection for some population units are ? or ? before drawing the sample. |
zero or unknown |
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What type of probability sampling can you calculate sampling error? Which one is more expensive? |
Probability sampling, Probability sampling, |
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Does non-probability sampling obtain information that is representative of the population? |
no information is obtained from a non-representative sample of the population |
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What are two advantages of non-probability sampling? |
Cheaper and faster than probability, reasonably representative if collected in a thorough manner |
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What is Convenience Sampling? |
A researcher's convenience forms the basis for selecting a sample: ex. students in my class |
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What is Judgment Sampling? |
A researcher exerts some effort in selecting a sample that seems to be most appropriate for the study |
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What is Snowball sampling? When is this used? |
The selection of additional respondents is based on referrals from initial respondents ex. friends of friends For low incidence samples or rare populations |
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What is Quota Sampling? |
Population is divided into cells on the basis of relevant control characteristics, and a convenience sample is drawn for each cell until the quote is met |
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What are two differences between Probability and Non-Probability Sampling?
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Non-Probability sampling is less time consuming and less expensive, the probability of selecting one element over another is not known and therefore the estimates cannot be projected to the population with any specified level of confidence , quantitative generalizations about populations can only be done under probability sampling |
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How does non-response affect sampling? |
nonresponse may turn any probability design into a non-probability design if the characteristics of nonresponse are not well understood |
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What is the definition of cohort study? |
a group of healthy people identified and followed over a certain time period to ascertain the occurrence of health-related events in order to investigate if the incidence of an event is related to an exposure |
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What is the basic approach to a cohort study? |
1. Cohort defined and sampled 2. participants are observed to assess exposure status (baseline) 3. Time passes 4. Participants are followed up to assess outcome status |
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What two groups are included in a cohort? |
general population (representative sample) and special groups such as occupation or exposures |
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How is exposure/outcome measured? |
interviews, questionnaires medical record review medical examination/test surveillance records |
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what is the definition of follow-up? what are some reasons for a loss of follow up? |
observation period following baseline assessment, migration, withdrawal, death, differential vs non-differential |
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what are 4 advantages to cohort? |
1. estimate incidence and risk which gives you a stronger evidence for causal inference 2. temporal relationships can be clearly observed 3. more statistical power so greater precision of effect measures 4. repeated measures can reduce bias |
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what are 4 disadvantages to cohort studies? |
1. loss to follow up
2. time and cost 3. difficultly of consistent 4. in longitudinal studies, standard regression models are not usable |
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what is the NA-ACCORD? |
it's the North American AIDS cohort collaboration on Research and Design, it's 25 collaborating cohorts that are designed to be widely representative of HIV care in the US And Canada |
