Flashcards in Sampling Deck (40)
What is a population or universe?
Any complete group with common characteristics
What is a population element?
Single member of a population
What is a census?
Investigation of all individual elements that make up a population
What is a sample?
- Subset of the larger population of interest
- This is the subset of group that the researcher will actually study or investigate
What is a population frame?
A list of all the elements in the population
What is a sample frame?
A list of all the elements in the population from which the sample may be drawn
What is sampling frame error?
An error which occurs when certain sample elements are not listed or are not accurately represented in a sampling frame
What is a sampling unit?
An element or group of elements subject to selection in the sample
What is inclusion/exclusion criteria?
The criteria potential participants must meet in order to be included in the study
What are the core statistical concepts?
* Descriptive statistics
* Inferential statistics
* Population parameters
* Sample statistics
What are descriptive statistics?
- Describe the data
- Measure of central tendency, frequencies, dispersion
What are inferential statistics?
- Project characteristics of a sample to an entire population
- Make an inference about a population from a sample
- Used in hypothesis testing
What are population parameters?
- Characteristics of the population
- Variable in a population or measure characteristics of the populaiton
- Greek letters as notation
- μ = ∑X/N
What are sample statistics?
- Estimates of population parameters
- Variables in a sample or measures computed from sample data
- English letters for notation
- X̅ = ∑X/N
What is the cost associated with sampling and the solution to this?
- A loss of information
- To make up for this loss we have to ensure that the sample is representative of the population
What does representativeness determine?
The representativeness of the sample determines the extent to which generalisable inferences can be made
What does the CLT imply?
- Suggests that the sampling distribution of the sample mean produces a normal curve
- As the sample size increases, the means of random samples taken form the population approach a normal distribution
- This means we have a representative sample - and our sample mean will be within close range of the true population mean
What is probability sampling?
Chance of selecting any particular member is known and is equal for all units (probability is non-zero)
What methods of probability sampling are there?
* Simple random
What is simple random sampling?
A sampling procedure that ensures that each elements in the population will have an equal chance of being included in the sample
What is systematic sampling?
Every nth name from a list (sampling frame) will be drawn
What is stratified sampling?
- Subsamples are drawn within different strata
- Strata are subgroups of elements that may be expected to have different parameters on a variable of interest
- Each stratum is more or less equal on some characteristic
What different types of stratified sampling are there?
- Subjects drawn from each stratum can be either dispropriationate or proportionate to the number of elements in the stratum
- Proportionate stratified sampling (20% of members from each stratum)
- Disproportionate stratified sampling (% of members disproportionate across stratum)
What is cluster sampling and what is the important aspect of it?
- Purpose is to sample economically while retaining the characteristics of a probability sample
- Primary sampling unit
- No longer the individual elements in the population
- Instead, a larger cluster of elements located in proximity to on another
What is non-probability sampling and when is it useful?
- Chance of selecting any particular member is unknown
- Useful when sampling frame cannot be created
What kinds of non-probabilty sampling are there?
* Convenience methods
* Purposive Methods
What types of convenience methods of sampling are there?
What is convenience sampling?
- The sampling procedure of obtaining the people or units that are most consistently available
- Least reliable of all sampling designs in terms of generalisability, but may be the only viable alternative when quick and timely information is needed
What is snowball sampling?
- Initial respondents are selected by probability methods
- Additional respondents are obtained form information provided by the initial respondents