sampling and populations Flashcards
lecture 5
By the end of the class students will:
Distinguish between a sample and a population
Explain why it is important to have a representative sample
Describe quantitative probability and non-probability sampling
techniques
Describe qualitative sampling techniques
Quantitative sampling
Random, Systematic, Convenience, Cluster, and Stratified.
represents a subset of the population
e.g mru students only hped hped is a subset
the sample must be like the population
define a population
it is a group that researchers generalize findings to
define a sample
A sample is the group taking part in the study
is a group within a population
types of sampling procedures, 2 categories
random probability
-Method that ensures population has equal probabilities of being
selected Strengthens the generalizability of the study’s findings
non-random probability
-Population does NOT have equal probabilities of being selected
* Findings might be generalizable, but unlikely
* Increases the risk of selection bias, which threatens internal validit
types of probability sampling
simple random
stratified
systematic
types of non-random probability
convenience
purposive
what is simple random?
name out of a hat
computer generated
equal opportunity for everyone to be selected
-The sample is representative of the population it is going to generalize to
-impartial and unbiased
what is systematic?
Researchers use lists or inventories of population, and names, and select people at regular intervals
e.g 100 selected but will pick one every 10 people
bias might be present
class list pick every 2nd student
what is stratified/
Population is divided into subgroups based on characteristics prior to random selection taking place
- Subgroups are fairly represented
- Proportionate vs. disproportionate
- Important when there is a specific characteristic
that needs to be in the sample
reduces bias
separating class into 1st 2nd and 3rd years
non probability sampling
Define what convenience is?
The researcher recruits participants that are familiar or convenient to them at that time and place
* Essentially asking people to volunteer
*based on who is available and willining ness
* “Take whatever they can get
A professor in biomechanics asked biomechanics people to be in a study
3 studies that we were asked to partake in
what is purposive sampling?
Identifies units (people, organizations, teams) that represent
characteristic of interest, such that, the sample is identified with
that purpose in mind
3 types
-Snowball
-expert
-quota
Purposive-what is Snowball ?
Word-of-mouth
* One person connects with their
network
* Useful for smaller or
vulnerable populations
Purposive-what is expert
identifying people
with a specific experience or
expertise in an area of interest
e.g athletes filling out a survey about fitness regime
e.g asking people with heart attacks to complete a questionnaire about their cardio health
Purposive-what is quota
researchers are given an amount such as 250 students in the health hped 125 female and 125 male
-can have errors and bias
