Epidemiology Flashcards
Define epidemiology:
A public health discipline basic science which studies the DISTRIBUTION and DETERMINANTS of disease in POPULATIONS to control disease and illness and promote health
Define the core function of epidemiology: pubic health surveillance
Surveying populations to find patterns of disease occurrence
- Data interpretation is a key skill, other key skills are designing & using data collection instruments, data management, and scientific writing and presentation
Define syndromes surveillance system:
Looks for predefined signs/symptoms of patients related to track able but rare diseases/conditions
Define epidemic:
Occurrence of disease clearly in excess of normal expectancy
Spans greater than a localized outbreak
Define Passive Surveillance System
Relies on healthcare system to follow regulations on required reportable diseases
Define active surveillance system:
Health officials go into communities to search for new disease cases
Define Outbreak:
An epidemic limited to a LOCALIZED increase in occurrence of disease (aka cluster)
Define Endemic:
The constant presence of a disease within a given area or population in excess of normal levels in other areas
Define Pandemic:
An epidemic spread world-wide (global health)
Define absolute difference:
A subtraction
Define relative difference:
A ratio
Define incidence:
New cases of disease
[aka Risk, aka Attack Rate, aka Cumulative Incidence]
Define prevalence
Existing cases of disease + new cases of disease
What causes prevalence to decrease?
If someone is cured or dies (removed from the pool)
What causes prevalence to go up?
When someone receives therapy to stay alive with the disease, such as insulin to treat diabetes
How do you calculate incidence?
(# of new cases of illness)/(# of people at risk of illness or in population)
[always subtract out (from the starting population, if known), those who’re not ‘at risk’ (already have the disease/outcome or are immune)]
What can incidence also be referred to as?
Risk, attack rate, or cumulative incidence
What is the equation used to calculate prevalence?
of existing cases of disease/# of persons in population
Define absolute difference:
A subtraction of 2 frequencies
Ex. 45 surgeries in males and 17 surgeries in females… 45-17 = 28, males had 28 more surgeries OR 17-45 = 28 (absolute value), females had 28 fewer surgeries
Define Relative difference:
A division of frequencies or proportions
Give an example of a relative difference frequency using 45 surgeries and 17 surgeries in females
45/17 = 2.6X the number of surgeries for males than females
OR
17/45 = 38%; Females had only 38% of the number of surgeries as males did
Give an example of a relative difference proportion using 45 surgeries in males and 17 surgeries in females
45 males with surgeries/ total number of males = X% surgeries in males
OR
17 women with surgeries/total number of women = X% surgeries in women
Define risk
Probability of outcome in an individual group
Explain how to calculate risk using smokers and nonsmokers as your example:
(# smokers with disease)/(total # of smokers)
OR
(# of nonsmokers with disease)/(total # of nonsmokers)
Define absolute risk reduction (ARR):
The risk difference of the outcome attributable to exposure difference between groups
How do you calculate absolute risk reduction (ARR)?
Good outcome% - bad outcome% = X%
The ARR tells you that for example the drug tested works X% better than the placebo
How is the relative risk reduction (RRR) calculated?
(AAR)/(R of the unexposed)
Ex. AAR/outcome of placebo = X%, so the drug lowers your risk of disease by X%
Define the number needed to treat/number needed to harm
Number of patients needed to be treated to receive the stated benefit or harm: 1/ARR = # needed to treat
Ex. Say ARR = 3.8% so, 1/.038 = 27 patients would need to be treated with the drug to reduce 1 disease/death case
Answer MUST be a whole number!!
Define Risk Ratio (RR or relative risk):
Ratios of the risks from 2 different groups
Risk of outcome in exposed)/(Risk of outcome in the non-exposed
What do risk, odds, and hazard ratios all have in common?
- All compare 2 groups and describe the likelihood of an event/outcome in 1 group compared to another
What does it mean if a risk, odds, or hazard ratio is equal to 1?
The event/outcome is equally likely for both groups being compared
What does it mean if a risk, odds, or hazard ratio is >1?
The event/outcome is MORE likely to occur in the comparison group
How is a risk, odds, or hazard ratio interpreted if it is >/= 2?
Use the phrase “X” times greater for interpretation
- The comparator group has X times greater odds of getting the disease
What are the 3 things to look for when interpreting ratios?
1) Group comparison orientation (drug vs. placebo or placebo vs. drug)
2) Direction of words (increased or decreased)
3) Magnitude (80% (1.8 times) or 20% (.8 times))
Define Odds
Frequency of an outcome occurring vs not occurring
- The frequency of exposure vs frequency of not being exposed
[in a 2x2 table, divide A/C or B/D]
What is the simplest way (shortcut) to calculate an odds ratio?
Cross multiply
A X D)/(B X C
Attributable risk is also known as ______
Absolute risk reduction (ARR)
[defines the risk difference of the outcome attributable to exposure difference between groups]
Calculation of incidence rate
of new cases of illness/person-time of people at risk of illness
[person-time: 100 person-years is 100 people followed for 1 year each; 10 people followed for 10 years each; 25 people followed for 4 years each, etc.]
How would you interpret a RR, OR, or HR of 1.8?
80% increased risk/odds/hazard
How would you interpret a RR of 0.25?
75% decreased risk/odds/hazard
T/F: When looking at the confidence interval for a ratio, if BOTH values are on the SAME side of 1.0 (equality) — it is ALWAYS statistically significant!
True
