Chapter 1: Epidemiology Flashcards
Epidemiology
study of distribution and determinants of health-related states within a population
Study of how disease often occurs in different groups of people and why
Endemic
expected rate of disease over time;
the disease is maintained without much variation within a region.
Epidemic
occurrence of disease in excess of the expected rate; usually presents in a large geographic span than endemics
Pandemic
worldwide epidemic
Epidemic curve
visual description (commonly histogram) of an epidemic curve is disease cases plotted against time; classic signature of an epidemic is a “spike” in time
Rates are usually described as per how many people?
per 100,000
Vital statistics are usually per how many people?
per 1,000
What is the general equation to determine rates in epidemiology?
actual cases/potential cases = numerator/denominator
What is incidence rate?
by definition
(IR) rate at which new events occur in a population
Formula for incidence rate?
(Number of new events in a specified period/number of persons “exposed to risk” of becoming new cases during this period ) x 10^n
Attack rate
by definition
cumulative incidence of infection in a group of people observed over a period of time during an epidemic, usually in relation to food-borne illness.
Attack rate formula?
number of exposed people infected with disease/ total number of exposed people
Another name for attack rate?
attack ratio
Prevalence
all persons who experience an event in a population
Prevalence formula?
Prevalence = (all cases of a disease at a given point and/or period/ total population “at risk” for being cases at a given point and/or period)/ 10^n
A case is counted in prevalence (in prevalence pot) until what events occur?
until death or recovery occur
Point prevalence
compares disease at different points in time in order to determine whether an outbreak is occurring.
Period prevalence
Also what conditions does it focus on acute or chronic?
prevalence during a specified period or span of time and focuses on chronic conditions.
Morbidity rate
rate of disease in population at risk (for both incident and prevalent cases)
Mortality rate
rate of death in a population (incident cases only)
What is crude rate?
actual measured rate in a whole population
What is specific rate?
actual measured rate for a subgroup of the population (e.g “age-specific or “sex-specific”)
Standardized rate?
adjusted to make groups equal on some factor
Another name for standardized rate?
adjusted rate
Crude mortality rate formula?
Crude mortality rate = deaths/population
Cause - specific mortality rate formula?
deaths from cause/ population
Case - fatality rate formula
deaths from cause/ number of persons with the disease and/or cause
Proportionate Mortality Rate (PMR) formula?
deaths from cause/ all deaths
Describe purpose of PMR.
how much a disease contributes to mortality rate (i.e what proportion of the mortality rate is due to that disease)
Purpose of cause-specific mortality rate?
how many people in the population are dying from that disease
Purpose of case-fatality rate?
how likely are you to die from the disease i.e fatality
The purpose for assessing the crude mortality rate?
to know the crude rate of people dying in the population
What is the goal of prevention in medicine?
reduce a person’s likelihood of becoming ill or disabled or of dying prematurely.
Primary prevention
Taking action to reduce the incidence of disease and health problems within the population, either through universal measures that reduce lifestyle risks and their causes or by targeting high-risk groups.
This type of prevention decreases disease incidence?
primary prevention
This type of prevention prevents recurrence and slow progression of a condition?
tertiary prevention
Secondary prevention
screens for risk factors and early disease, permitting timely and effective intervention and curative treatment.
Tertiary prevention
focuses on people who are already affected by a disease. The goal is to improve quality of life by reducing disability, limiting or delaying complications, and restoring function.
This type of prevention effort decreases disease prevalence.
secondary prevention
What is the gold standard screening test for HIV detection?
Western blot
Positive and Negative meaning in screening test refers to what?
test result
True or False in screening test refers to what?
If the test result is truly positive or negative
TP
tested positive, sick
FP
tested positive; actually healthy
TN
Tested negative; actually healthy
FN
Tested negative; actually sick
Sensitivity?
probability of correctly identifying a case of disease
Formula for sensitivity?
TP/(TP +FN)
False negative rate formula?
1-sensitivity
Specificity
probability of correctly identifying disease-free persons.
Formula for specificity.
TN/(TN+FP) = true negatives/ (true negatives + false positives)
False positive rate formula?
1-specificity
If a test has a high specificity, then a positive result indicates the (presence or absence) of a disease?
presence of a disease
If a test has a high sensitivity, then a negative result indicates the (presence or absence) of disease?
absence of a disease
Mneumonic for telling the difference between sensitivity and specificity?
SN-N-OUT (sensitive test - negative rules out disease)
SP-I-N (specific test-positive rules in disease)
A good screening test should have which of the following epidemiological properties?
A. high specificity
B. low specificity
C. low sensitivity
D. high sensitivity
E. high positive predictive value
F. low negative predictive value
D. High sensitivity
What is PPV?
positive predictive value: probability of disease in a person who receives a positive test result. (probability that a person with a positive test is a true positive (i.e has the disease)
Negative predictive value?
NPV: probability of no disease in a person who receives a negative test result (the probability that a person with a negative test result is a true negative (i.e does not have the disease)
Formula for PPV?
TP/(TP+FP) true positives/ (true positives + false positive)
Formula for NPV?
TN/(TN+FN) true negatives/ (true negatives + false negatives)
Accuracy?
the degree to which a measurement represents the true value
Accuracy formula?
(TP + TN)/(TP + TN + FP + FN) or
(true positives + true negatives)/ total screened patients
The higher the prevalence the (greater or less) the PPV? NPV?
greater the PPV; less the NPV
The lower the prevalence the greater or lesser the PPV? NPV?
less the PPV; greater the NPV
Would increasing the incidence have an effect on sensitivity or PPV?
Would have no effect on either because a screening test can only detect current presence or absence of disease, not the onset.
Selection bias
sample selected is not representative of the population
Another name for selection bias?
sampling bias
Solutions for mitigating selection bias?
random, independent sample; weight data
What is a solution to measurement biases like Hawthorne effect?
have control groups
Another name for experimenter expectancy?
Pygmalion effect
What is experimenter expectancy?
expectations are inadvertently communicated to subjects who then produce the desired effect
Solution for experimenter expectancy?
use double-blind design
What is lead time bias?
gives a false estimate of survival rates (e.g patients seem to live longer with the disease after it is uncovered by a screening test
Solution to lead time bias?
use life-expectancy to assess benefit
What is recall bias?
When subjects fail to accurately recall events in the past
What is the solution for recall bias?
confirmation
What is late-look bias?
when individuals with severe disease are less likely to be uncovered in a survey because they die first
What is the solution to late-look bias?
stratify by disease severity
What is confounding bias?
factor being examined is related to other factors of less interest
What is the solution to mitigating confounding bias?
combine the results from multiple studies, meta-analysis
What is design bias? What is the most common cause of this?
when parts of the study do not fit together to answer the question of interest;
most common issue is a non-comparable control group
Solution for mitigating design bias?
random assignment, i.e., subjects assigned to treatment or control group by a random process
Example of Berkson’s bias
only using hospital records to estimate population prevalence.
Example of nonrespondent bias?
when survey participants are unwilling or unable to respond to a survey question or an entire survey
so people in study will be different than people not included and won’t represent the whole
(i.e) if you are researching workload among managers in a supermarket chain and you decide to collect your data via a survey, managers with the largest workload are less likely to answer your survey questions due to constraints on their time.
