Sampling

Question 1

Population vs. Sample

Answer 1

A population is the total group of interest

A sample is a subgroup of the group of interest

Question 2

What is a target population?

Answer 2

the group to whom researchers wish to apply their research findings.

Question 3

What is an accessible population?

Answer 3

the pool of potential research participants who are actually available for a given study.
*A smaller subset of the target population

Question 4

Inclusion vs. Exclusion Criteria for subject identification

Answer 4

Inclusion criteria define in more detail the characteristics that individuals from the population of interest must possess to be eligible for study (demographic, clinical, and/or geographic).
Exclusion criteria define in more detail characteristics that will make individuals ineligible for consideration as subjects (may also be demographic, clinical, and/or geographic).

Question 5

What are the two general approaches to subject selection?

Answer 5

1) Probabilistic Sampling

2) Non-probabilistic Sampling

Question 6

What is Probabilistic Sampling?

Answer 6

refers to the use of a method for randomly selecting subjects for participation in a study
*Generally unbiased, however it is more expensive and time consuming

Question 7

What are the 4 types of probabilistic selection methods?

Answer 7

1) Simple Random Sampling
2) Systematic Sampling
3) Stratified Sampling
4) Cluster Sampling

Question 8

Describe Simple Random Sampling

Answer 8

The most basic probabilistic sampling method in which each potential subject has an equal chance of being selected
For Example: numbers drawn out of a hat

Question 9

Does Simple Random Sampling increase or minimize sampling error and why?

Answer 9

It minimizes sampling error because each potential subject has an equal chance of being selected

Question 10

When is simple random sample selection useful?

Answer 10

When selecting from several hundred or fewer subjects

Question 11

Describe Systematic sampling

Answer 11

This type of subject selection method is used when the subject candidate pool is in the thousands. Subjects are selected in specified intervals such as all evens, odds, certain pattern, etc.

Question 12

In systematic sampling what subject is selected at random?

Answer 12

Only the first one, then all remaining subjects are chosen based on their numerical distance

Question 13

Describe Stratified Sampling

Answer 13

A more complex probabilistic selection method used when investigators have an interest in capturing homogenous subgroups within the population
For Example: selecting 10 freshman, 15 sophomores, 15 juniors, and 10 seniors

Question 14

Describe cluster sampling (aka multistage sampling)

Answer 14

This type of probabilistic selection method first randomly selects a large subgroup (cluster), and then selects smaller units from these clusters at random
For example: first randomly select 10 schools, then randomly select 1 class from each school, and then randomly select 4 students from each class

Question 15

What is Non-probabilistic Sampling?

Answer 15

refers to methods for choosing subjects that do not involve a random selection process.
*Easier to implement and cost less

Question 16

What are the 3 types of non-probabilistic selection methods?

Answer 16

1) Convenience Sampling
2) Snowball Sampling
3) Purposive Sampling

Question 17

Describe convenience sampling

Answer 17

The most basic non-probabilistic method in which researchers select subjects who are readily available (such as students).

Question 18

Describe snowball sampling

Answer 18

A non-probabilistic method in which researchers start with a few subjects and then recruit more via word of mouth from the original participants.

Question 19

Describe Purposive Sampling

Answer 19

A non-probabilistic method in which researchers make specific choices about who will serve as subjects in their study
**This method is very biased

Question 20

What is effect size?

Answer 20

The magnitude of the difference between two mean values (change in status)

Question 21

How is effect size calculated?

Answer 21

is the mean change score divided

by the standard deviation of the pre-treatment score

Question 22

What is power?

Answer 22

The probability that a statistical test will detect a relationship between two or more variables.
In other words the ability of a statistical test to find a significant difference that really does exist.

Question 23

How do you calculate power?

Answer 23

1 - β

* β is type II error which is accepting a false null hypothesis

Question 24

How large must a sample size be?

How large is a very good sample size?

Answer 24

Need at least 30 subjects

100 is very good

Question 25

Describe a single case design

Answer 25

A type of quasi-experimental study in which one subject receives in an alternating fashion both the control condition (A) followed by the experimental condition (B)

Question 26

What are the 3 variations of the single case design we discussed in class?

Answer 26

1) A-B-A
2) A-B-A-B
3) A-B-C

Question 27

Describe A-B-A design

Answer 27

There is a baseline data period (A) followed by the experimental treatment period (B) after which they return to the baseline condition (A).

Question 28

When is the A-B-A design useful?

Answer 28

When experimenters want to observe behavior before treatment, during treatment and after treatment.

Question 29

Describe A-B-A-B Design

Answer 29

There is a baseline data period (A) followed by experimental treatment measurement (B) the treatment is withdrawn (A), and then the treatment is re-introduction (B).

Question 30

When is the A-B-A-B design used?

Answer 30

If you are designing an experiment in which you want to see an improvement

Question 31

Describe A-B-C Design

Answer 31

There is a baseline data period (A) followed by experimental treatment measurement (B) which is then followed by another experimental treatment

Question 32

What is DF?

Answer 32

Degrees of Freedom

Statistical concept indicating the number of values within a distribution that are free to vary.

Question 33

How do you calculate degrees of freedom?

Answer 33

n-1