Samples and Populations Flashcards
Define populations
The entire collection of people that we’re interested in studying
Define samples
A selection of individuals from the larger population that we’re interested in studying
What are the 4 reasons why we sample instead of studying the population directly?
1) Save time (It will take forever to collect data from the population, too many people)
2) Save money (Collecting data from the population is expensive, production cost, payment to participants)
3) Easy access (Accessing the population is difficult and impossible)
4) Results from a sample is generally sufficient (Pattern of results doesn’t change much even if we have data from everyone)
How do we sample? List 7 ways
1) Random sampling
2) Systematic sampling
3) Stratified proportional sampling
4) Stratified disproportional sampling
5) Cluster sampling
6) Opportunity sampling
7) Snowball sampling
What sampling is when each member of the population has an equal chance of being selected (usually quasi-random)?
Random sampling
What is Random Sampling?
When each member of the population has an equal chance of being selected (usually quasi-random)
What sampling draws from the population at fixed intervals and is problematic in populations with a periodic function?
Systematic Sampling
How do you conduct Random Sampling?
Usually assign a person in the population to a number and use a random number table to select a sample
What is Systematic Sampling?
Sampling that draws from the population at fixed intervals and is problematic in populations with a periodic function
How do you conduct Systematic Sampling?
You’d select members of the population at a regular interval
e.g. Selecting every 15th person on a list of the population
What are the 2 types of Stratified Sampling?
1) Proportional
2) Disproportional
What is Proportional Stratified Sampling?
When specified groups appear in numbers proportional to their size in the population
e.g. If the population was 60% female and 40% male, the sample would also be 60% female and 40% male to represent the population
What sampling involves specified groups appearing in numbers proportional to their size in the population?
Proportional Stratified Sampling
How do you conduct Proportional Stratified Sampling?
e.g. If the population was 60% female and 40% male, the sample would also be 60% female and 40% male to represent the population
(you would take 120 females and 80 males in a sample size of 200)
What is Disproportional Stratified Sampling?
When specified groups which are not equally represented in the population, are selected in equal proportions
e.g. If the population was 60% female and 40% male, the sample would instead have a proportion of 50% female and 50% male
What sampling involves specified groups which are not equally represented in the population, being selected in equal proportions?
Disproportional Stratified Sampling
How do we conduct Disproportional Stratified Sampling?
e.g. If the population was 60% female and 40% male, the sample would instead have a proportion of 50% female and 50% male
(you would take 100 females and 100 males in a sample size of 200)
What is Cluster Sampling?
When a researcher samples an entire group or
cluster from the population of interest
What is one precaution of Cluster Sampling?
We must be careful to not generalise a whole population from a cluster
What sampling involves a researcher sampling an entire group or cluster from the population of interest?
Cluster Sampling
How do we conduct Cluster Sampling?
e.g. Divide a population info clusters (districts, schools, neighbourhoods) and then randomly select some of these clusters as samples
What is Opportunity/Convenience Sampling?
When we use people who are easily available as our sample
What sampling involves using people who are easily available as a sample?
Opportunity/Convenience Sampling
How do we conduct Opportunity/Convenience Sampling?
e.g. Asking members of the population of interest if they would like to participate in the study
What is one problem with Opportunity/Convenience Sampling?
This can lead to a biased sample
What is Snowball Sampling?
When you recruit a small number of participants and then use those initial contacts to recruit further participants (recruit using connections)
Which sampling involves recruiting a small number of participants and then using those initial contacts to recruit further participants?
Snowball Sampling
What is one limitation and benefit of Snowball Sampling?
Con = Biases the sample
Pro = Useful if you want to recruit very specific populations
How do you conduct Snowball Sampling?
Recruit participants through existing participants
e.g. We ask existing participants if they could recommend and nominate additional potential participants
Define External validity
The ability to generalise our results outside of the lab
Define Population validity
Is our sample representative of the population?
Define Ecological validity
Does the behaviour measured reflect
naturally, occurring behaviour?
Do our results apply to people outside of laboratory settings/ in real-world settings?
What are the 3 factors that help you decide on a sample size?
1) Design (subjects design, number of IVs or IV levels)
2) Response rate of the potential participants
3) Heterogeneity of population
What are the 3 factors that help you decide on a sample size?
1) Design (subjects design, number of IVs or IV levels)
2) Response rate of the potential participants
3) Heterogeneity of population
What sampling is this based on?
You want to get shoppers’ opinions on a set of logos for a new product, you ask every 100th person who passes you on a central shopping street on a Saturday morning.
Systematic sampling
What sampling is this based on?
You want to ask psychiatrists about the limitations of current services offered to people with psychosis. You contact a few psychiatrists, and ask them if they know other people who might take part
Snowball sampling
What sampling is this based on?
You want to understand more about factors contributing to exam anxiety in undergraduate students. You design an online survey and send it out to the whole undergraduate mailing list for students at the UoM. The sample is comprised of individuals who complete the survey within a week of it being sent out.
Opportunity sampling
Which of the following sampling methods is most free of bias?
a. Snowball sampling b. Convenience sampling c. Systematic sampling d. Opportunity sampling
C
It is often the case that as internal validity increases, __________________ decreases.
a. internal consistency b. construct validity c. external validity d. content validity
C
When our measure is not reflective of real world behaviour we have a problem with…
a. Ecological validity b. Divergent validity c. Criterion validity d. Population validity
A
Jen is conducting some research into attitudes about teenage pregnancy. She goes into a cafe on campus and ask the students there if they would mind completing her questionnaire. Jen is using…
a. Stratified sampling b. Snowball sampling c. Cluster sampling d. Opportunity sampling
D
