Sampling/Validity

Question 1

Population

Answer 1

larger group to which research results are generalized

Examples:
* people with knee osteoarthritis
* elderly with a history of falls
* recreational athletes
* DPT students

Question 2

Sample

Answer 2

• a subgroup of the population used for estimating characteristics of that population
• More feasible
• More economical

Question 3

Sample Bias

Answer 3

Choosing a sample that over or under-represents certain attributes may bias the measurement

Examples
* Return to sport after ACL reconstruction:
– Sample = NFL athletes
– Sample = city rec league participants

Question 4

Goal of Inclusion/Exculsion Criteria

Answer 4

• Goal is to research a sample that accurately represents the population of interest
• Limit the influence of confounding subject characteristics (increases confidence in the study results):
  Examples
  – comorbities
  – concurrent treatment

Question 5

Inclusion Criteria

Answer 5

description of the traits that qualify someone to be a subject

Question 6

Exclusion Criteria

Answer 6

description of factors that preclude participation

Question 7

The more strict inclusion and exclusion results in…

Answer 7

• Less ability for the research to apply to the general public or larger populations BUT…
• Minimizes selection bias and increases the ability to make cause/effect relationships

Question 8

Types of Sampling Techniques

Answer 8

• Probability Sampling
• Nonprobability Sampling

Question 9

Probability Sampling

Answer 9

• Randomization involved at some point
• Preferred method

Question 10

Nonprobability Sampling

Answer 10

• Randomization NOT involved at any point
• Must question the ability to generalize to the population
• Suspect that the sample is biased in some way
• Far more common in clinical research

Question 11

Simple Random Sampling

Answer 11

• Each member of the population of interest is equally likely to be selected
• Random number generator selects them, requires the entire population to be known

Difficult for studies due to inclusion/exclusion criteria not being able to apply to everyone

Question 12

Systematic sampling

Answer 12

• Participants chosen from a list (every Kth name)
• Ex: Every 9th name on the list
• Limitation: Requires an entire list of the population.

Question 13

Stratified Sampling

Answer 13

• Random sampling from subgroups
• Guarantees representation of the entire population, allows for analysis of subgroups seperately
• Ex: Grades of OA in individuals, sorted by severity

Question 14

Cluster Sampling

Answer 14

• Divide the population into clusters (often by geographical)
• Randomly sample within the cluster
• Measure all nuits within sampled clusters and extrapolate to the entire population

Question 15

Convenience Sampling

Answer 15

• Use of volunteers very common in PT literature
• Chosen based on availability (clinical site)
• May also be recruited from flyers/signs
• Volunteers tend to have greater motivation
• Especially relevant for experimental studies as volunteers may more strictly adhere to the intervention (Volunteer bias)
• Treatments more likely to show an effect

Question 16

Consecutive Sampling

Answer 16

• Enrollment of first x number of subjects
• People looking to be involved rather than you looking for them

Question 17

Quota Sampling

Answer 17

• Non-probability equivalent of stratified sampling
• Subgroups of subjects that vary on some characteristic are recruited/enrolled until appropriate sample size is reached
• Ex: Individuals with knee OA grades I-IV

Not always easy to get all quotas (# of participants) filled for a specific subgroup

Question 18

Purposive Sampling

Answer 18

• Sample selected for a specific purpose
• Ex: Effect of school size on ACL injury rate
• Commonly used in qualitative studies

Question 19

Snowball Sampling

Answer 19

• Begins by identifying someone who meets the inclusion criteria for your study
• Ask them to recommend others who they may know who also meet the criteria

Question 20

Why is having a massive number of participants not good?

Answer 20

A greater number of people in your results may manipulate because we tighten up the numbers and given more room for error. Too much room for error gets rid of the ability to see difference.

Question 21

Statistical significance does not mean…

Answer 21

it is clinically significant

Question 22

How do you choose the number of subjects needed for a study?

Answer 22

• In general a larger subject pool is better
• Research design
• Calculations

Question 23

What does a valid study rely on to prove cause-effect relationships?

Answer 23

• It relys on the ability to rule out effects of extraneous variables
• If these variables are not controlled would be considered confounding variables

Question 24

Internal Validity

Answer 24

• Amount that a cause-and-effect relationship is free from the effects of confounding variables
• Our confidence that a change in one things caused a change in the outcome

Question 25

Requirements for Internal Validity

Answer 25

* Temporal Precedence -- Change in outcome must ocur AFTER a change in treatment * Covariation of cause and effect -- The outcome only occurs in the prescence of the intervention * No plausible alternative explanations * Types of threats to approach -- Single group threat -- Multiple group threat -- Social threats

Question 26

Single group threat

Answer 26

* Only one group in your study (no control group)

Question 27

Multiple Group Threat

Answer 27

* Multiple group threats (More than one group in your study but groups not equivalent or not treated equally) * Differences between groups that affect a cause/effect relationship; influenced by subject selection

Question 28

Social Threat

Answer 28

* Interaction of subject with the investigator * Blinding of subjects midigates this threat

Question 29

Types of single group threats

Answer 29

* History * Maturation (Changes occur as a result of a passing of time) * Testing (Repeated test taking may improve test scores * Instrumentation (Change in instrumentation) * Mortality/Attrition (Subjects die due to old age) * Regression to the mean (statistical phenomenon that affects studies based on extreme scores from a single test; outlyers are within their own extreme results in a more normal curve)

Question 30

Types of Multiple Group Threats

Answer 30

* Selection-history (groups have different experiences between pretest and posttest; Ex: performing the test at different institutions) * Selection-maturation (groups may naturally change at different rates) * Selection-testing (pretest affects group differently; people who get pain after test vs no pain effects on performance) * Selection-instrumentation (Instrumented data is not consistent between groups) * Selection-regression (stimulus and experience don't match; high goes low, low goes high)

Question 31

Types of Social Threats

Answer 31

* Performance Bias (Motivation to suceed is different) * Contamination (Members of the control group receive intervention) * Co-intervention (Subjects seek/receive another form of treatment that influences the DV) * Different Therapists * Attention Bias (Hawthorne Effect: People's behavior and performance improves following new or increased attention; Reverse Hawthorne Effect: People's behavior and performance decline if they perceive they are not recieving equal attention/care.

Question 32

Threats to External Validity

Answer 32

* People (selection process creates a sample that does not represent the population) * Place (Dependent variable greatly affected by the setting in which the data were collected) * Ecological Validity (Study atmosphere resembles real-life * Time/Technology (Old studies technology not as accurate)

Question 33

Detection Bias

Answer 33

* Number of variables -- Too few: increase likelihood the treatment effect was missed -- Too many: increase likelihood difference is by chance * Adjustments made to statistics to account for multiple comparisions -- If so: bias favors control group ("conservative") -- If not: bias favors experimental group ("liberal") * Recall bias (investigators use self report tools and ask subjects to recall past events)