- An element is an object on which a measurement is taken.
- A population is a collection of elements about which we wish to make an inference.
- Sampling units are non-overlapping collections of elements from the population that cover the entire population.
- A sampling frame is a list of sampling units.
- A sample is a collection of sampling units drawn from a sampling frame.
- Parameter: numerical characteristic of a population
- Statistic: numerical characteristic of a sample
- Sampling can save money.
- Sampling can save time.
- For given resources, sampling can broaden the scope of the data set.
- Because the research process is sometimes destructive, the sample can save product.
- If accessing the population is impossible; sampling is the only option.
- Every unit of the population has the same probability of being included in the sample.
- A chance mechanism is used in the selection process.
- Eliminates bias in the selection process
- Also known as probability sampling
- Every unit of the population does not have the same probability of being included in the sample.
- Open the selection bias
- Not appropriate data collection methods for most statistical methods
- Also known as nonprobability sampling
Simple Random Sample
- Uses a random number table or a random number generator to select n distinct numbers between 1 and N, inclusively.
- Easier to perform for small populations
- Population is divided into non-overlapping subpopulations called strata
- A random sample is selected from each stratum
- Proportionate -- the percentage of thee sample taken from each stratum is proportionate to the percentage that each stratum is within the population
- Disproportionate -- proportions of the strata within the sample are different than the proportions of the strata within the population
- Systematic sampling is often used instead of random sampling. It is also called an Nth name selection technique.
- After the required sample size has been calculated, every Nth record is selected from a list of population members.
- Population is divided into nonoverlapping clusters or areas
- Each cluster is a miniature, or microcosm, of the population.
- A subset of the clusters is selected randomly for the sample.
Convenience Sampling: sample elements are selected for the convenience of the researcher
Judgment Sampling: sample elements are selected by the judgment of the researcher
Quota Sampling: sample elements are selected until the quota controls are satisfied
Snowball Sampling: survey subjects are selected based on referral from other survey respondents