RM - Sampling Flashcards
What is bias?
A systematic distortion.
What is an opportunity sample?
A sample of participants produced by selecting people who are most easily available at the time of the study.
What is population?
The group of people that the researcher is interested in studying, from whom a sample is drawn, and about whom generalisations can be made.
What is a random sample?
A sample of participants produced by using a random technique so that every member of the target population has an equal chance of being selected.
What is sampling?
The method used to select participants, such as random, opportunity and volunteer sampling, or to sample behaviours in an observation, such as event or time sampling.
What is a stratified sample?
A sample of participants produced by identifying subgroups according to their frequency in the population. Participants are then selected randomly from the subgroups.
What is a systematic sample?
A sample obtained by selecting every nth person (where n is any number). This can be a random sample if the first person is selected using a random method; you then select every nth person after that.
Uses a predetermined system.
What is volunteer bias?
A form of sampling bias (distortion) because volunteer participants have special characteristics, such as usually being more highly motivated than randomly selected participants.
What is a volunteer sample?
A sample of participants that relies solely on volunteers to make up the sample. Also called a self-selected sample.
What is another name for subgroups?
Strata
What are the strengths of opportunity sampling?
Easiest method as you just use the first suitable participants you can find, which means it takes less time to locate your sample than if using one of the other techniques.
What are the limitations of opportunity sampling?
Inevitably biased because the sample is drawn from a small part of the population.
E.g. stopping people in town on a Monday morning would not include working professionals or people from rural areas.
What are the strengths of random sampling?
Unbiased as all members of the target population have an equal chance of selection.
What are the limitations of random sampling?
Need to have a list of all members of the population and then contact all of those selected, which may take some time.
What are the strengths of stratified sampling?
Likely to be more representative than other methods because there is a proportional and randomly selected representation of subgroups.
What are the limitations of stratified sampling?
Very time consuming to identify subgroups, then randomly select participants and contact them.
What are the strengths of systematic sampling?
Unbiased as participants are selected using an objective system.
What are the limitations of systematic sampling?
Not truly unbiased/random unless you select a number using a random method and start with this person, and then select every nth person.
What are the strengths of volunteer sampling?
Give access to a variety of participants (e.g. all the people who read a particular newspaper) which may make the sample more representative and less biased.
What are the limitations of volunteer sampling?
Sample is biased in other ways because participants are likely to be more highly motivated and/or with extra time on their hands. They might be more highly motivated to be helpful, or more broke and needing the money offered for participation. This results in a volunteer bias.
What is the lottery method and how is it done?
Easiest way to obtain a random selection is to draw numbers or names ‘out of a hat’. This is sometimes called the lottery method.
- Obtain a list of all the people in the population.
- Put all the names in a lottery barrel or hat.
- Select the number of names required.
What are the three random techniques?
The lottery method
Random number table
Random number generators
What is the random number table method and how is it done?
An alternative random technique is to use a printed table of random numbers.
- This time every member of the population is given a number.
- The starting point in the table is determined blindly by placing your finger anywhere.
- If your population is less than 100 you only need 2 digit numbers so read the table 2 digits at a time. If your population consists of only 80 people then you would ignore number 93 and carry on.
What is the random number generators technique and how is it done?
Calculators have functions that generate random numbers as do computers and apps on phones.
- Number every member of the population.
- Use a random number generator to get a random number between 1-100 etc.
