Data Collection Flashcards
Define population
A whole set of data/items that are of interest
Define census
Observes or measures every member of a population
Define sample
Selection of observations taken from a subset of the population
What are the advantages of a census?
Should always give you a completely accurate result
What are disadvantages of a census?
Time consuming, expensive, cannot be used if the testing process destroys the item and hard to process large quantities of data
What are the advantages of a sample?
Less time consuming and expensive than a census, fewer people have to respond and there is less data to process than a census
What are the disadvantages of a sample?
Data may not be accurate and the sample may not be large enough to give information about small subset groups of a population
What are sample units?
Individual units of a population
What is a sampling frame?
A list of all the items you want to study in your population
What are the characteristics of random sampling?
Every member of the population has an equal chance, sample should be representative and it helps to remove bias
What are the three methods of random sampling?
Simple random sampling, systematic sampling and stratified sampling
What do you need to carry out simple random sampling?
A sampling frame
What are the two methods of choosing numbers?
Generating random numbers and lottery sampling
In systematic sampling, how are elements chosen?
Regular intervals from an ordered list meaning that there are equal gaps between those who are chosen
In stratified sampling, how is the population divided?
Into mutually exclusive strata
What should the ratio of each strata be?
1:1 meaning that each strata sample should be equal
How do you calculate the number of sampled in a stratum?
(Number of stratum/number of population) x overall sample size
What are the advantages of simple random sampling?
Free of bias, easy and cheap to implement for small populations/samples and each sampling unit is known and has an equal chance of selection
What are the disadvantages of simple random sampling?
Not suitable when population size/sample size is too large and a sampling frame is needed
What are the advantages of systematic sampling?
Simple, quick to use and suitable for large populations/samples
What are the disadvantages of systematic sampling?
Sampling frame needed and it can introduce bias if the sampling frame is not random
What are the advantages of stratified sampling?
Accurately reflects the population structure and guarantees proportional representation of groups within a population
What are the disadvantages of stratified sampling?
Population must be clearly classified into district strata and selection within each strata suffers from the same disadvantages as simple random sampling (sample frame needed and not suitable for large sample size due to expense and time)
What are the two types of non-random sampling?
Quota sampling and opportunity sampling
What happens in quota sampling?
An interviewer or researcher selects a sample that reflects the characteristics of a whole population and they are divided into groups based on given characteristics
What does the size do each quota sampling group determine?
It determines the proportion of the sample that should have that characteristic
What happens if in quota sampling a person refuses to be interviewed?
You ignore them and move on
What happens in opportunity sampling?
You take a sample from people who are available at the time to be studied and who fit your criteria
What is opportunity sampling also known as?
Convenience sampling
What are the advantages of quota sampling?
Allows a small sample to represent the population, no sampling frame needed, quick. easy and inexpensive and it always easy comparison between different groups within a population
What are the disadvantages of quota sampling?
Could lead to bias, population must be divided into groups which is costly and inaccurate, non-responses are not recorded and increasing scope of study increases number of groups adding time and expense
What are the advantages of opportunity sampling?
Easy to carry out and inexpensive
What are the disadvantages of opportunity sampling?
Unlikely to provide a representative sample and highly dependent on individual researcher
Describe quantitative data
Data associated with numerical observations
Describe qualitative data
Associated with non-numerical observations
Describe continuous variable
Can take any value in a given range
Describe discrete variable
Can take only specific values in a given range
Describe class boundaries
Maximum and minimum values in class
Describe midpoints
Average of the class boundaries
Describe class width
Difference between upper and lower class boundaries
