Biostatistics Flashcards
What is continuous data?
Data with a logical order
Values that continuously increase or decrease – have theoretically infinite options
Examples: age, height, weight, time, BP, temperature
What are types of discrete (categorical) data?
Nominal and ordinal
What is nominal data?
Categories – order does not matter
Examples: gender, ethnicity, marital status, mortality
What is ordinal data?
Categories are ranked in logical order but difference between categories is not equal Examples: NYHA functional class I-IV; 0-10 pain scale
What is the spread of data?
How much it varies
What is the range of data?
Difference between highest and lowest value
What is the standard deviation (SD) of data?
Indicates how spread out the data is, and to what degree the data is dispersed away from the mean
What is Gaussian distribution?
Normally shaped “bell curve”
On a bell curve, ___% of values fall into one standard deviation of the mean, ___% fall into 2 standard deviations of the mean
68%
95%
Independent vs dependent variables
Independent: Changed by researcher
Dependent: affected by independent variables
What does the null hypothesis state?
No statistically significant difference between groups
***Researcher tries to reject this
What does the alternative hypothesis state?
There is a statistically significant difference between groups
***Researcher tries to prove this
What is the alpha value?
Threshold for rejecting null hypothesis
“error margin”
Usually 0.05 or 5%
If p-value is ___ alpha, null is rejected and result (is/is not) statistically significant
Less than alpha
is
What is the confidence interval? How is it calculated?
Provides same info about significance as p-value, plus precision of the result
1-alpha = CI
If a confidence interval (CI) includes ____ it is not statistically significant
0: when comparing difference data
1: when comparing ratio data
Which indicates high precision, narrow or wide CI?
Narrow
What does a 95% confidence interval indicate?
You are 95% sure that the true value falls between the range given
Type 1 error = false _____
Type 2 error = false _____
Type 1: false positive
Type 2: false negatives
What does the study power indicate?
The probability that a test will reject the null hypothesis correctly
Power to avoid type II error
If beta is 0.2, what is the study power?
80%
What is relative risk?
Risk in the exposed group (treatment) divided by risk in the control group
Risk formula
Total number of subjects in a group
Relative risk formula
Risk in control group
What does relative risk of 1, >1, or <1 mean?
1 = no difference in risk between group >1 = greater risk in treatment group <1 = less risk in treatment group
Relative risk reduction calculation
5 risk control group
OR
1-RR
What is relative risk reduction?
Indicates how much risk is reduced in treatment group
Absolute risk reduction calculation
(% risk in control group) – (% risk in treatment group)
What does an absolute risk reduction (ARR) of 12% mean?
12 out of every 100 patients benefit from treatment
Number needed to treat calculation
1/(risk in control group – risk in treatment group)
OR
1/ARR
Which way do you round number needed to treat (NNT)? Number needed to harm (NNH)?
NNT – round up
NNH – round down
What is odds ratio (OR)?
Used to assess the odds of an outcome occurring with an exposure compared to odds of the outcome occurring without the exposure
What is hazard ratio?
Rate at which an unfavorable event occurs within a short period of time
Hazard ratio (HR) calculation
Hazard rate in control group
What is a composite endpoint?
Combined endpoints into one measurement
What test should be used with numerical/continuous data with one group
One-sample t-test
What test should be used with numerical/continuous data with two groups (e.g treatment and control)
Independence/unpaired student t-test
What test should be used with numerical/continuous data with three or more groups
ANOVA
What test should be used with discrete/categorical data with two groups
Chi-squared test or Fisher’s exact test
What is correlation
Statistically technique that is used to determine if one variable changes or is related to another variable
What is regression used to describe?
The relationship between a dependent variable and one or more independent variables or ho much the value of the dependent variable changes when the independent variables changes
What does sensitivity/specific indicate?
Sensitivity – true positive; positive in patients with the condition
Specificity – true negative; negative in patients without the condition
What is intention-to-treat analysis?
Includes data for all patients originally allocated to each treatment group even if they did not complete the trial according to study protocol
What is per-protocol analysis?
Includes data for all patients who completed the study according to protocol
What are equivalence and noninferiority trial designs?
Equivalence – demonstrates new treatment has ~equal effect the old treatment
Non-inferiority – new treatment is no worse than current standard based on predefined non-inferiority margin
What do forest plots provide?
Cis for difference data or ratio data
Characteristics of case-control studies
Retrospective
Compare cases to controls
Characteristics of cohort studies
Limitations
Retrospective or prospective
Compare patients with an exposure to those without an exposure
Limitations: can be influenced by confounders
Characteristics of randomized controlled trials
Prospective
Compare patients who were randomly assigned to groups
Characteristics of meta-analyses
Analyzes the results of multiple studies
Characteristics of systematic review article
Summary of the clinical literature that focusses on a specific topic or question
Characteristics of case report or case series
Describes adverse event or condition in a single patient (report) or a few patients (series)
What does pharmacoeconomics do?
Identifies, measures, and compares the costs and consequences of pharmaceutical products and services
What are some indirect and intangible medical costs?
Indirect: lost work time, low work productivity, morbidity, mortality
Intangible: pain, suffering, anxiety, fatigue
