Epidemiology Flashcards
What is Odds Ratio?
Ratio of odds of exposure in the diseased group to odds of exposure in the control group (ad/bc from 2x2 contingency table).
What is Relative Risk?
Proportion of the absolute risk of disease in exposed group to the absolute risk of disease in unexposed group (a/(a+b) divided by c/(c+d)from 2x2 contingency table) aka incidence of disease in exposed/incidence of disease in unexposed group.
What is Attributable Risk?
Attributable Risk is the difference between the risk of disease in exposed group and risk of disease in unexposed group (a/(a+b) minus c/(c+d) from 2x2 contingency table).
What is incidence of a disease?
The occurrence of new cases of a disease in a population during a specified time period
What is prevalence of a disease?
The total number of existing cases [new + old] of a disease in a population at a specific time point [day or time; aka Point Prevalence] or during a specified time period [month or year; aka Period Prevalence]
What are 2 main types of epidemiological studies?
Descriptive and Analytical
What are the 3 essential components studied in descriptive epidemiology?
Time, place, and person/animal
[who, what, when, where]
True or False: Observational studies are always only descriptive?
False; Observational studies can be descriptive and or analytical/experimental
What are 2 types of analytical studies?
Observational and Experimental
What are 2 types of analytical observational studies?
- Cohort
- Case control
Name 2 types of experimental analytical studies?
- Clinical trials
- Community trials or ecological studies.
What are primary determinants of a disease?
Factors which can exert a major effect in inducing a disease (e.g. and infectious agent causing an infectious disease)
What are secondary determinants of a disease?
Predisposing, enabling and or reinforcing factors
What is infectivity of a microorganism?
The ability of a micro-organism to infect, survive and multiply within a host
(No of index cases/no of population at risk)
Pathogenicity of a micro-organism refers to?
The capacity to cause disease; depends on agent properties such as toxin production, tissue damaging enzymes etc.
(number of disease cases/total number infected)
What is virulence of a micro-organism?
Virulence is the ability to produce serious illness or death, indicated by fatality rate.
What is an epidemic curve?
Is a histogram displaying the number of cases [y-axis] of an illness by date of illness onset [x-axis}
What information does an epidemic curve provide?
Outbreak information on pattern of spread, magnitude, outliers, time trend, incubation period of an illness.
What is the threshold level of an epidemic?
The minimum population density required to allow a contact transmitted epidemic to commence
(epidemic occurs when population density is above the threshold level)
Which measure determines the epidemic threshold level?
Basic reproduction number R0; epidemic occurs at R0 > 1
Parasite population will only establish in community if?
R0 > 1
Name 6 epidemiological disease patterns?
sporadic, endemic, hyper-endemic, epidemic, outbreak, and pandemic
What is a sporadic disease pattern?
Disease occurrence at irregular intervals (time and space)
Describe an endemic?
Occurrence of a disease in a defined population at the usual rate, at moderately regular intervals.
What is a hyper-endemic disease pattern?
Gradual increase in the occurrence of a disease at rates above the endemic level but at epidemic proportions.
Describe an epidemic?
Sudden increase in the incidence of a disease, above the expected levels of disease occurrence for a population in a specific area.
What is an outbreak?
Outbreak is an epidemic of a smaller magnitude or geographic extent
What is a pandemic?
Is an epidemic that has crossed international boundaries and has spread across continents.
Prevalence = ?
Incidence x Duration
How to calculate crude death rate?
(Total # of deaths from all causes in one year) / (# of persons in the population @ midyear)
Age-Specific Mortality Rate
Total # of deaths from all causes in one year for a specific age/age group / Total # of people in that specific age group @ midyear
Cause-Specific Mortality Rate?
Total # of deaths from a specific disease in one year/Total # people in the pop. @ midyear)
Case Fatality Rate (CFR)?
Total # of deaths d/t a disease during a specific time period/ Total # of individuals with the specified disease; calculated mostly for acute diseases
Standardized Mortality Ratio (SMR)?
Observed # of deaths per year/ Expected # of deaths per year
What is sensitivity of a test?
The ability of the test to correctly identify those who HAVE the disease
TP / (TP + FN)
Sensitivity of a test if aka?
True Positive Rate; TP rate
What is specificity of a test?
The ability of the test to correctly identify those who DO NOT HAVE the disease
TN / (TN + FP)
Specificity of a test if aka?
True Negative Rate; TN rate
How is positive predictive value of a test defined?
The probability that an individual who tests positive truly has the disease
PPV= TP/(TP + FP)
How is negative predictive value of a test defined?
The probability that an individual who tests negative truly does not has the disease
NPV= TN/(TN + FN)
true or false: PPV depends on prevalence of a disease in population.
True
How can PPV be calculated if sensitivity (SN), specificity (SP) of a test as well as prevalence of disease in a population are known?
PPV= (SN) (Prevalence)/ (SN) (Prevalence) + (1-SP) (1-Prevalence)
How can NPV be calculated if sensitivity (SN), specificity (SP) of a test as well as prevalence of disease in a population are known?
NPV= (SP) (1-Prevalence)/ (SP) (1-Prevalence) + (1-SN) (Prevalence)
