Lecture 7: Populations & Samples Flashcards
What is a population?
The entire set of people, animals, or things that the study is interested in gathering information about
What is a sample?
A set of subjects from the population we’re interested in, which we use to make inferences about the population at large
Why do we use samples?
Taking from the entire population is often impossible
Describe the distribution when we use a larger sample
They closely resemble each other and the population they come from! (In terms of shape, mean, standard deviation)
Describe the distribution when we use a smaller sample
Distributions vary more from one sample to the next and don’t often resemble the population very closely
What are the 3 good characteristics of a sample?
- Adequate size - bigger = reliable
- Representative of the population we’re interested in
- Random sample to avoid bias - equal chance for anyone of being in the sample
3 Sources of bias in sampling
- Convenience sampling
- Self-selection/Volunteer sampling
- Dropouts
What’s a convenience sample?
Using whatever subjects are conveniently accessible
What’s self-selection/volunteer sampling
A sample that is biased to include people with personalities that make them likely to volunteer eg. people who have time, who like the study topic
Who is most likely to drop from a study
- People who can’t handle the conditions of the study eg. in depression people who don’t improve, in school people who can’t handle the education
What is sampling error?
The DISCREPANCY between the SAMPLE and the POPULATION
How do we minimize sampling error?
Using a LARGE and REPRESENTATIVE SAMPLE
Descriptive statistics
Statistics used to describe the sample data itself
Inferential statistics
Statistics used to make inferences about the population from the sample
