Biostatistics and Methods of Epidemiology Flashcards by Jasper Viloria

What is the appropriate measure of central tendency in qualitative data such as gender, religion, or nationality?

Mode

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4, 6, 2, 2, 4, 3, 2, 1, 7
Mean?
Median?
Mode?

Mean
Median 3
Mode 2

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Average

Sum of observations divided by the number of observations

Mean

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The observation that occurs with greatest frequency

Mode

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Middle observation in a series of ordered observations

e.g. the 50th percentile

Median

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Epidemiology can be defined as the study of the ___ and determination of ___ of disease in ___

distribution
frequency
humans

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What is the sampling unit in epidemiologic studies in the identification of causal factors?

A group of individuals

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The ultimate goal of an EPIDEMIOLOGIC INVESTIGATION: To institue ___, ___, and ___ to avoid more cases

curative
preventive
control measures

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Studies both the DISTRIBUTION OF DISEASES in human populations and the DETERMINANTS OF THE OBSERVED DISTRIBUTION

Epidemiology

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Epi?

Demos?

Upon

People

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Began as the study of infectious diseases

Epidemiology

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Epidemiology began as the study of infectious diseases. Later on, it expanded to include the study of ___ disease, ___ of health care, ___ of health care, and ___ and ___ health

chronic
organization
delivery
occupational
environmental

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Study of the distribution of diseases in animals

Epizootiology

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Antigenic drift or shift?

Most likely the cause of changes in a certain strain that allows infection despite adequate vaccination

Antigenic drift

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Antigenic drift or shift?

Partial immunity or mutation to a less virulent strain

Antigenic drift

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A sudden change in the molecular structure of a microorganism and produces new strains. This results to little or no acquired immunity to these new strains and is the explanation for new epidemics or pandemics (novel strains)

Antigenic drift

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A slow and progressive change in the antigenic composition of microorganisms. this alters the immunological responses of individuals and a populations susceptibility to that microorganism

Antigenic drift

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This would decrease the rate of infection by decreasing the probability that a susceptible person would come into contact with an infected person.
Would this affect the clinical presentation of those infected? Y/N

Herd Immunity

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Community’s Reaction to Disease:

Occurrence of a number of cases of disease in excess of normal occurrence of expectancy

Epidemic

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Community’s Reaction to Disease:

Epidemic involving many countries

Pandemic

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Community’s Reaction to Disease:

Occurrence of few and unrelated cases

Sporadic

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Community’s Reaction to Disease:

Constant occurence

Endemic

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No cases on record, disease not there from the beginning, disease has been eradicated e.g. small pox (Variolavirus 1980)

Absence of disease

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Association between LBW and maternal smoking during pregnancy
What type of study to be used?

Cohort

Study: Exposure and outcome are measured at the same point in time E.g. prevalence study

Cross sectional

Study: | Prospective studies in which an intervention is applied

Clinical trials

Refers to the groups of subjects who are followed forward in time to see which ones develop the outcome

Cohort

Study: Clinical characteristic or outcome form a single clinical subject or event (n=1) Control: none

Case Report

Study: Prevalence study Determines in each member of the population the presence or absence of a disease and other variables at one point in time Control: none

Cross Sectional

Study: Assesses the association of risk factor and disease Causality cannot usually be determined

Cross Sectional

Study: Clinical characteristic or outcome from a group of clinical subjects or evens (n>1) Control: none

Case Series

Study: | Population group exposed to a risk factor is followed over time compared with a group not exposed to the risk factors

Cohort

Study: Outcome is disease incidence in each group Prospective To establish causality

Cohort

Study: Can determine icidence and causal relationships if there is statistical association between risk factor and disease Control: Population at risk versus population not at risk

Cohort

Study: Very useful for studying conditions which very low incidence or prevalence Rare diseases

Case-control

Study: | Weak establishment of causality

Case-control

Study: Identifies a group of people with the disease (case) and compares them with a suitable comparison group without the disease (control)

Case-control

Study: Retrospective Assesses many risk factors for disease Can help determine causal relationships --- but weakly

Case-control

Study: Weakest because outcome has already happened Cannot assess incidence and prevalence of disease

Case-control

E.g. Study of the causes of a rare form of leukemia; limited funding; large database that is only a few years old What study will you recommend?

Case control

Problem of Cohort study? | What question does a cohort study answer?

Loss to follow up and attrition | What will happen?

Problem of Case control study? | What question does a case control study answer?

Recall | What is happened?

What question does a cross sectional study answer?

What is happening?

``` A new screening test is applied to a representative sample of 1000 people in the population. Positive diseased: 90 Positive well: 60 Negative diseased: 10 Negative well: 840 Sensitivity? Specificity? PPV? ```

Sensitivity: how many true positives among diseased? 90/100 90% SNOUT Specificity: how many true negatives among well? 840/900 SPIN Positive predictive value: how many diseased among positives? 90/150

Total number of cases in a population at a given time; all cases, old or new; chronic

Prevalence

Number of new cases in a population per unit time; new, acute

Incidence | Incidence is new incidents

Number of true positives divided by number of all people with disease

Sensitivity PID: positive in disease (PID is a sensitive topic!) SNOUT: sensitivity rules out

High sensitivity is desirable for a ___ test, to rule ___!

SCREENING | OUT

High specificity is desirable for a ___ test, to rule ___!

CONFIRMATORY | IN

Number of true negatives divided by the number of all people without the disease

Specificity NIH: negative in heath SPIN: sensitivity rules in

Number of true positives divided by the number of people who tested positive for the disease

PPV

The probability of having a condition given a positive test. "Is it really positive?"

PPV

An increase in PPV will lead to an/a ___ in prevalence

increase

Number of true negatives divided by the number of people who tested negative for the disease

NPV

The probability of not having a condition, given a negative test. "Is it really negative?"

NPV

Unlike sensitivity and specificity, predictive values are dependent on the ___ of a disease. The higher the ___ of a disease, the ___ the PPV

prevalence prevalence higher

``` E.g. The absence of valvular calcification in an adult suggests that severe valvular aortic stenosis is not present. --- Valvular calcification is/has: Sensitive? Specific? High PPV? Low NPV? ```

Sensitive Sensitive test: one that is positive in most patients with disease. If the absence of a characteristic rules out a disease, then the test is sensitive; hardly anyone with the disease has a negative test