Fall 2023 Flashcards
What is a natural disease?
The usual course of disease over time
Prognostic Factor
Something (environmental factor, personal characteristic, behavior) that can be used to estimate the chance of recovery or recurrence
Risk Factor
Something (environmental factor, personal characteristic, behavior) that increases the chance of developing a disease
Prospective Cohort Study
1- Identify Sample at Risk
2- Asses Risk Factors @ Interest
3- Measure who develops outcome/not
Incidence (rate of developing)
Risk Ratio
Retrospective Case-Control Study
1- Collect data/review chart or records to determine who had exposure/risk factor or not
2- Identify “Cases” and “Controls”
Prevalence
Odds Ratio
Prevalence
Number of people who have the outcome at a given point in time / # of people at risk at that point in time
Incidence
Number of new people who develop the outcome over a period of time / # at risk during that period
Risk Ratios // Relative Risk
Likelihood with which those that have the risk factor will develop the outcome compared to those that don’t have the risk factor (prospective)
Odds Ratios
Likelihood with which those who have a condition (or outcome) have been exposed to a risk factor compared to those who don’t have the condition (retrospective)
Relative Risk - Cross Tabulation
a/(a+b)
_______
d/(c+d)
Odds Ratio - Cross Tabulation
ad
___
bc
RR/OR > 1
RR/OR - 1 = __ * 100% =
___% increase in Risk/Odds
RR/OR < 1
1 - RR/OR = __ * 100% =
___% reduction in Risk/Odds
Rule with RR/OR Confidence Interval
If it includes 1, there is no significance
Unadjusted or Crude Odds Ratio
- 2x2 Table or Logistic Regression
- Accounts for One Relationship
- One Independent, One Dependent
Adjusted Odds Ratio
- Calculations using Logistic Regression
- Accounts for Multiple Variables that Might Affect Relationship
- Multiple Independent Variables
Internal Validity
Relationship between independent (intervention) and dependent (outcome) variable
Tight control of experiment leads to higher internal validity
Efficacy of Treatment
External Validity
Extent to which the independent (intervention) and dependent (outcome) can be generalized outside of the experiment
Tight control of experiment can decrease external validity
Effectiveness of Treatment
Efficacy
Benefit of an intervention in an experimental setting
-Control of many variables
Effectiveness
Benefit of an intervention in a real-world setting
-Less control of variables, bias
Threats to External Validity
Selection
Setting
History
Intervention/Protocol
Construct Validity
Statistical Inference
Estimating characteristics of a population (parameter) from sample data (statistics)
-Population aggregate of persons/objects/events that meet a specific criteria
Probability Sampling
Simple Random
Systemic
Cluster
Stratified Random (Proportional / Disproportional)
Non-Probability Sampling
Convenience (Consecutive / Volunteer)
Quota
Purposive
Inclusion Criteria
Primary traits of the target and accessible population that qualifies them as a subject
Exclusion Criteria
Factors that would preclude someone from being a subject
WEIRD Bias
Western (White)
Educated
Industrialized
Rich
Democratic
Construct Validity
Abstract behavior or event that cannot be directly observed, but is inferred from other relevant observable variables
Operational Definition
The measure(s) used by a particular study to quantify the construct
Parametric Tests
-Estimation of Population
-Assume Normal Distribution
-Often continuous/discrete variable
Ex: T-test, ANOVA
Non-Parametric Tests
-Not based on population parameters
-Assuming Non-Normal Distribution
-Nominal or Ordinal Variables
Ex: Mann-Whitney U Test, Wilcoxon Signed Rank Test, Friedman/Kruskal-Wallis ANOVA, Chi-Square or Fisher Exact Test
ANOVA
More than 2 groups (independent or dependent/repeated measures)
T-Test
Between two groups (independent or unpaired)
Within one group (before & after intervention) (dependent or paired)
alpha
% chance that we found a difference but there wasn’t one (chance of type 1 error)
p
How rarely we would expect a difference this large (found in the study) by chance
Effect Size - Index/Ratio
Difference between groups (treatment + error) / variability within groups (error) = Cohen’s d
Cohen’s d
Index/Ratio
0.2 - 0.5 = small
0.5 - 0.8 = medium
> 0.8 = large **lower variability/rule of thumb too large
Type I Error (alpha)
Conclude an effect is real when it is actually due to chance // found a difference when there really isn’t
-extremely large samples make it easier to find significant effect
1 - .95 = .05(alpha) —> 5% risk of Type 1 Error
Type II Error (beta)
Conclude an effect is due to chance when it is actually real // found no difference when there really is
-not enough subjects per group to detect difference
.8 power = 1 - beta(.20) —> 20% risk of Type 2 Error
a priori
planned comparisons prior to data collection
can correct for Type 1 Error with alternate t-test (Bonferroni)
Post-hoc
unplanned comparisons made after data is analyzed (ANOVA)
can correct for Type I error with alternate t-tests (Tukey’s)
Confounding Variable
Anything other than the independent variable that could potentially affect the dependent variable
Stratification
Equal recruitment in each group to decrease confounding variable (known prior to recruitment)
Blocking
Randomized sequence in pre-determined blocked groups to ensure equal distribution between groups
Bias
Any tendency which prevents unprejudiced consideration of a question
Selection Bias
Selecting non-equivalent groups
RCT
Maturation Bias
Time on the health condition recovery (natural history)
RCT
Concealment
When the person who is screening the participants for eligibility does not know the randomization sequence
Performance Bias
When participants or personnel perform differently based on knowing what group they are in
Detection Bias
When the personnel assessing the outcomes perform differently based on knowing what group participants are in
Blinding
Reduces bias by keeping researchers and/or participants ignorant of group assignments and/or research hypotheses (single/double/assessor)
Attrition Bias
Effects of loss of participants during the trial (drop outs)
Standardized Reporting
Reporting number loss to follow-up at each time point (intention to treat analysis performed)
Intention to Treat
Data analyzed according to group assignment, regardless if subject completes study or “switches” group
Attrition > 20% then question results
Testing Bias
Confounding effects of repeated testing or use of an outcome