Data Collection Flashcards
Define population
The whole set of items that are of interest
Define sample
A selection of observations taken from a subset of the population which is used to find out information about the population as a whole
Define census
Every element of the population is surveyed which is rare, expensive and labour intensive
Define sampling unit
Individual units of a population (eg a resident)
Define sampling frame
List of sampling units formed when sampling units are numbered or named (eg list of residents)
Define random sampling method and identify the 3 types
Every element of the population has an equal chance of being selected. Stratified sampling, systematic sampling and simple random sampling
Explain a simple random sample
Need a sampling frame. Each person is allocated a unique number and a selection of these numbers is chosen at random (by generating random numbers using a computer or calculator or random number table, or by lottery sampling which involves numbers being written on tickets and the required number of tickets for the sample are drawn out)
Explain systematic sampling
The required elements are chosen at regular intervals from an ordered list but the first element is chosen at random. Eg if a sample size 20 was required from a population of 100, you would take every fifth person after the first person you picked (out of the first five) because 100/20 is 5
Explain stratified sampling
The population is divided into mutually exclusive strata (males and females for example) and a random sample taken from each , the proportion of each strata sampled should be the same. (Number in stratum divided by number in population) x overall sample size
Identify the 2 types of non random sampling
Quota and opportunity/convenience sampling
Explain quota sampling
Population divided into groups according to a givenm characteristic, size of each group determines the proportion of the sample that should have that characteristic. Interviewer meets people, discusses their group and allocates them into the correct quota, this continues until all quotas are filled (ignore people when the quota they fit into is full)
Explain convenience sampling
Taking a sample from people who are available at the time the study is carried out and who fit the criteria you are looking for
What are the 2 advantages of taking a census?
It should give a completely accurate result, everyone’s views will be known
What are the 4 disadvantages of a census?
Time consuming, expensive, cannot be used when the testing process destroys the item, hard to process large quantity of data
What are the 3 advantages of a sample?
Less time consuming and expensive than a census, fewer people have to respond, less data to process than a census
What are the 2 disadvantages of a sample?
Data may not be as accurate, sample may not be large enough to give information about small sub groups of the population
What are 3 advantages of simple random sampling?
Free of bias, easy and cheap to implement for small populations and small samples, each sampling unit has a known and equal chance of selection
What are the 4 disadvantages of simple random sampling?
Not suitable when the population size of the sample size is large, could be errors in sampling frame, person chosen from sampling frame could be absent on day of survey (if the survey is at work), gaining access to the whole sampling list can present challenges in schools/unis
What are the 3 advantages of systematic sampling?
Simple and quick to use, suitable for large samples and large populations, clustered selection eliminated (a phenomenon in which randomly chosen samples are uncommonly close together in a population, random samples can only deal with this by increasing the number of samples or running more than one survey which can be expensive alternatives)
What are the 3 disadvantages of systematic sampling?
The systematic method assumes the size of the population is available or can be reasonably approximated, population needs to exhibit a natural degree of randomness along the chosen metric because of the population has a type of standardized pattern the risk of accidentally choosing very common cases is more apparent, greater risk of data manipulation with systematic sampling because researchers might be able to construct their systems to increase the likelihood of achieving a targeted outcome rather than letting the random data produce a representative answer
What are the 2 advantages of stratified sampling?
Sample accurately reflects the population structure, guarantees proportional representation of groups within a population
What are the 4 disadvantages of stratified sampling?
Population must be clearly classified into distinct strata, selection within each stratum suffers from the same disadvantages as simple random sampling, overlapping can be an issue if there are subjects that fall into multiple subgroups, finding an exhaustive and definitive list of an entire population can be challenging
What are 4 advantages of quota sampling?
Allows a small sample to still be representative of the population (improves the representation of particular strata (groups) within the population, as well as ensuring that these strata are not over-represented), no sampling frame required so is quick and easy, inexpensive, allows for easy comparison between different groups within a population
What are 5 disadvantages of quota sampling?
Possible that the selection of units to be included in the sample will be based on ease of access and cost considerations resulting in sampling bias, not possible to make statistical inferences from the sample to the population, population must be divided into groups which can be costly or inaccurate, increasing scope of study increases number of groups which adds time and expense, each unit from the population must only belong to one stratum