Exam One - Sampling in PT literature Flashcards
Generalization
process of drawing conclusions (that apply to all) from a small number of observations
population
larger group to which results are generalized
sample
a subgroup of the population used for estimating characteristics of that population
inclusion criteria
description of the traits that qualify someone to be a subject
to whom can we generalize these results to?
exclusion criteria
description of factors that preclude participation
factors are generally confounding to the results
What is the value of inclusion and exclusion criteria?
- define your population
- limit the influence of confounding subject characteristics
efficacy
very strict inclusion and exclusion criteria minimize selection bias and increase your ability to make cause/effect conclusions
efficacy trials =
high control, limited bias
effectiveness
less strict inclusion and exclusion criteria. increase risk for bias, limit control, and offer less confidence in cause/effect conclusions
effectiveness trials
limited control, greater bias
probability sampling
randomization involved at some point in the process
non-probability sampling
no randomization
must question ability to generalize
far more common in clinical research
What are the main types of probability sampling
- simple random sampling
- systematic sampling
- stratified sampling
- cluster sampling
simple random sampling
each member of the population of interest is equally likely to be selected
(requires entire pop to be known)
systematic sampling
participants chosen from a list (every Kth name)
no independent chance of being selected
need a list of the entire population
stratified sampling
limits sampling error associated with pure random sampling b/c its possible to randomly over/undersample on some key variable
- random sampling from subgroups
cluster sampling
divide pop into clusters, randomly sample clusters, measure all units within sampled clusters and then extrapolate to entire population
What are some types of nonprobability sampling
1 - convenience sampling
2 - quota sampling
convenience sampling
“they are there” very common
- subjects chosen based on availability
- subjects typically from one clinical site
- volunteers tend to have greater motivation
- enrollment typically as participants become available
quota sampling
- nonprobability of stratified sampling
0 subgroups of subjects that vary on some characteristic are recruited until appropriate sample size is reached
The more subjects you analyze, the _________ confident you can be that your sample represents the pop characteristics you with to measure
more
internal validity
the degree that a cause and effect relationship is free from the effects of confounding variables
- our confidence that a change in one thing CAUSED a change in the outcome of interest
what are 3 requirements for internal validity
1 - temporal precedence
2 - covariation of cause and effect
3 - no plausible alternative explanations
temporal precendence
the change in outcome must occur after a change in the treatment
covariation of cause and effect
outcome only occurs in the presence of the intervention or greater intervention, greater outcome
no plausible alternative explanation
rule out competing reasons for the observed change in the outcome of interest besides the intervention
What are some threats to internal validity?
- history
- maturation
- testing
- instrumentation
- mortality/attrition
- regression to the mean
history effects
events unrelated to the study that may influence the dependent variable
maturation effects
changes occur in the outcome of interest as a result of the passing of time or time might change the outcome measure
testing effects
repeated test taking may improve scores
instrumentation effects
a change in instrumentation that affects the outcome of interest
mortality/attrition effects
subjects are “dying” with respect to your study (dropping out)
regression to the mean effects
statistical phenomenon that affects studies where groups are selected based on extreme scores to a single test
How do you stop the outcome of interest being affected by any interaction of the subject with the investigator
blinding the subjects and/or investigator
What are two types of social threats to internal validity?
- performance bias
- attention bias
Performance bias (2 types)
- contamination
- conintervention
performance bias
inconsistency in the application of the experimental condition
contamination
members of the control group receive the intervention
cointervention
subjects seek/receive another form of treatment that influences the DV during the experiment
attention bias (2 types)
- hawthorne effect
- reverse hawthorne effect
hawthorne effect
people’s behavior and performance improve following any new or increased attention
reverse hawthorne effec
peoples behavior and performance decline if they perceive they are not receiving equal attention and care
recall bias
error associated with self-report tools asking for subjects to recall past events
external validity
can you generalize your results to other patients, settings, or times?
people threat to EV
selection process yields sample that does not represent the pop the researches hope to apply the results to
place threat to EV
outcomes affected by the setting in which the data were collected
ecological validity
study atmosphere resembles real life
time threats to EV
results of an experiment specific to the era the data were collected
