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PHC 6000: Sampling
Introduction to epidemiology: Sampling
| Question | Answer |
|---|---|
| What are probability samples? | Any method of sampling that utilizes some form of random selection |
| What are non-probability samples? | Methods of sampling that does not involve random selection |
| What are the four possible combinations of exposure/outcome that participants in a cross-sectional study can have? | -Exposure & outcome -Exposure & no outcome -No exposure & outcome -No exposure & no outcome |
| When should nonparametric methods of analysis be used? | When sample is not a random or probability sample or when a sample doesn't fit a particular distribution |
| What is essential to generalize to the source population? | Representativeness (validity) |
| What is a sampling unit (element) | Subject under observation on which information is collected |
| What is an element also called? | Sampling unit |
| What is a sampling frame? | List of all the sampling units from which the sample is drawn |
| What is a sampling scheme? | Method of selecting sampling units from sampling frame |
| What is a sampling fraction? | Ratio between sample size and population size |
| What is probability sampling? | Each member of the population has a known chance (probability) of being included in sample |
| When are nonprobability samples useful? | When probability samples are not feasible |
| What are some situations in which probability samples may not be feasible? | Groups that cannot be penetrated/hard to reach (e.g., prostitutes, prescription drug users) |
| What is one of the main problems with nonprobability samples? | They are less generalizable |
| Sampling error is easily measured using what type of sampling methods? | Simple random sampling and systematic random sampling |
| What are the disadvantages to simple random sampling? | -Need complete list of units -Doesn't always achieve best representativeness -Units may be scattered/poorly accessible |
| What are the disadvantages to systematic sampling? | -Need complete list of units -Periodicity |
| What are the advantages to stratified sampling? | -Can acquire info about whole population and individual strata -Precision increased if variability within strata is less than between strata = homogenous |
| Give an example of variability within strata being less than between strata. | There is less variability within females than between males and females |
| What are the disadvantages to stratified sampling? | -Can be difficult to identify strata -Loss of precision if there are small numbers in individual strata |
| What is a solution to small numbers in individual strata? | Sample according to proportion of stratum population; weight according to size |
| What are the advantages to cluster sampling? | -Provides logistical advantage -Complete list of sampling units within population not required -Less travel/resources required |
| What are the disadvantages to cluster sampling? | Potential problem is that cluster members are more likely to be alike than those in another cluster |
| What needs to be considered when choosing a sampling method? | -Population to be studied -Size/geographical distribution -Heterogeneity with respect to variables -Availability of list of sampling units -Level of precision required -Resources available -Data collection method (e.g., phone, interview) |
| Which variable should be used to determine sample size? | Choose the variable that would require the largest sample size |
Created by:
AlneciaPHS
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