BIO stats Flashcards
Continuos data what are the types and the differences of each and examples/
Interval and Ratio
Ratio has a meaningful zero age, ht, wt
Interval no meaningful zero, celsius (equal distance between values)
Discrete data is also referred to as?
What are the different types and examples of them?
Nominal: Order is arbitrary (gender, ethnicity)
Ordinal ranked in logical order pain scale 0,10
The mean is preferred for what type of data?
continuos and normally distributed data
What is the mean preferred for?
preferred for ordinal or continuous data that is skewed
The mode is preferred for what data?
nominal
Continuous data tends to follow what?
A normal distribution
68% fall within how many?
95%?
within 1 SD
within 2 SDs
When is skewed data likely to occur?
If sample size is small and or there are outliers
What is the best measure of central tendency when you have outliers?
How can the distortion of outliers be reduced?
Median is the best judge
Distortion can be reduced with increased sample size
Right and left skew?
low values to the right positive right skew
left, negative left skew
If the alpha is 5% what does the p-value need to be to reject the null hypothesis?
Confidence interval =?
CI=1- alpha
When are the results statistically significant?
Is there a difference with ratio data? (RR, OR, HR)
If the confidence interval doesnt include zero
Statistically significant if values CI does not contain 1
What is a type 1 error?
Rejecting the null when the null is true
saying there is a difference when there is none
p value correlated to probability of type 1
Type 2?
Accepting the null when the null is false (b)
What is power?
the probability that the test will reject the null hypothesis correctly
How is power calculated?
1-B
why is absolute risk reduction more useful?
because it includes the reduction in risk and the incidence rate
ARR of 12% in metoprolol vs placebo trial what does it mean?
means 12% out of every 100 pts benefited from tx
How do you round NNT?
NNH?
When do you use absolute value?
52.1 round to 53
NNH: 41.9 round down to 41
When calculating NNH use ARR absolute vlue
What kind of studies use odd ratio instead of relative risk?
How do you calculate OR?
Case-controlled studies
OR= AD/BC
When are hazard ratios used?
survival analysis (analysis of death or disease progression)
HR and OR interpretation?
If OR or HR = 1 the event rate is the same
> 1 event rate is higher in treatment group
<1 event rate is lower in tx group
Notes on composite endpoints
must be similar in magnitude and have similar meaningful importance to the pt
Use the composite endpoint value instead of adding them all up
What test should be used for continuous data?
normal distribution (parametric test)
Nonnomral (nonparametric)
When is a T-test used?
when is a student t-test usd?
with continuous and normally distributed data
Student t-test
2 independent variables, medication and placebo
When is an analysis of variance used? (ANOVA)
or F-test is used to when continuous data with 3 or more sample groups
What test is used when nominal or ordinal data is used?
Chi-squared test
What test is used for correlation?
What is it used for?
Spearmans ranked order correlation (RHO)
ordinal or ranked data
What test is used for continuous data correlation?
Pearsons Correlation Coeffieicent
r which indicates the strength and direction of correlation (-1 to +1)
When are regressions used?
What are the 3 types and what are they each used for?
described the relationship between a dependent variable and one or more independent variables
commonly used in observational studies
Linear: continuous data
Logical for categorical
Cox regression for categorical in survival analyisis
If the test result is positive what is the likelihood of having the disease?
If the test is negative what is the likelihood of not having the disease?
If a sensitivity is 100% what does that mean?
test will be positive in all patients with the condition
100% specificy?
100% of negative patients will not have the disease
Specificity is the percentage of?
True negative results
Sensitivity and Specificity Formulas
Sensitivity: A/(A+C) x 100
Specificity: D/(B+D) x 100
What two ways can data from clinical trials be analyzed?
Intention to treat and per protocol analysis
NonInferiority and Equivalence trials
Equivalence new drug is as good as
Non-inferiority: new drug is not much worse
When are forest plots used?
Composite endpoints in one study
or
meta-analysis
Forest plots
- Boxes show the effect estimate, in meta-analysis the bigger the box the more effect from the study is seen
- Diamonds: represent pooled results from multiple studies
- Horizonal line is the length of the confidence interval
- Vertical line: Line of no effect, left illustrates significant benefit, to the right shows significant harm
Case control study
- Pts with disease (cases) to those without (control),
- Retrospective
- OR,
Cohort Study
Compares outcomes of a group of pts exposed and not exposed
Groups are followed prospectively
Cross-sectional survey
- Estimates the relationship between variables and outcomes (prevalence) at one particular time (cross section) in a defined population
Case report and case series
- Describes an adverse reaction or a unique condition that appears in a single pt (case report) or a few pts (series)
- No real conclusions can be drawn
RCTs
- Compared an experimental tx group to a control (placebo or existing tx) to determine which is better, subjects with the design characteristics (inclusion criteria)
Benefits and Limitations of Cross over RCT
- Pts serve as there own control this minimizes effects of confounders
- A washout period between tx is needed to minimize influence of the first drug during second tx
Factorial design
Randomized to more than the usual to
- Evaluates multiple interventions in a single experiment
- With every arm added the more subjects you need
Meta-Analysis
- Smaller studies can be pool instead of performing a large one
- Studies may not be uniform, validity can be compromised if lower quality studies are weighted equally to higher studies
Systemic Review article
- Summary of clinical literature that targets something specific
- Inexpensive
Methods for pharmacoeconomic analysis? 4
- Cost effectiveness analysis
- Cost-minimization analysis
- cost utility analysis
- cost benefit analysis
What do pharmacoeconomic studies serve to do
Guide optimal healthcare resource allocation
What model is used to evaluate outcomes?
ECHO
- Economic
- Clinical
- Humanistic Outcomes
Incremental cost effectiveness ration calculation
C2-C1/ E2-E1
When is cost-minimization analysis used?
when two or more interventions have shown equivalence in outcomes and the cost of the interventions are compared
Cost Benefit Analysis
comparing benefits and costs of an intervention in terms of monetary units
Advantage of Cost Effectiveness Analysis
outcomes are easier to quantify most common analysis
Input dollars output clinical (LDL level)
Disadvantage: unable to directly compare different types of outcomes (Diabetes program vs. Asthma program: cant do that)
What is Cost Utility Analysis?
specialized form of CEA that include a quality of life component
using quality adjusted life years (QALY) and disability adjusted life years (DALYs)
About quality not quanitity
takes into account morbidity and mortality
