disease detectives

sensitivity

percentage of people diseased who test positive

specificity

percentage of people not diseased who test negative

point prevalence

number of cases in a defined population at a point in time

period prevalence

number of cases in a defined population over a period of time

incidence

number of new cases in a defined population over a defined period

risk

chances of person getting sick within a certain period of time

rate

same as risk but divide by person years, not defined population

odds

number of events divided by number of non events

excess risk

increase in risk from background risk once exposed

relative risk/risk ratio

compares the probability of an event occurring in an exposed or treated group with the probability of the same event in an unexposed

case control study

• gather based on outcome, investigates common potential exposures

• retrospective

• cheap

• low evidence strength

• multiple exposures

• can observe rare outcomes

cohort study

• based on exposure

• prospective

• long and expensive

• stronger evidence

• multiple outcomes

• rare exposures

randomized control trial

interference

cross sectional study

observes from a single point in time

Bradford Hill criteria for causation

• Strength: A small association does not mean that there is not a causal effect, though the larger the association, the more likely that it is causal

• Consistency: Consistent findings observed by different persons in different places with different samples strengthens the likelihood of an effect.

• Specificity: Causation is likely if there is a very specific population at a specific site and disease with no other likely explanation.

• Temporality: The effect has to occur after the cause (and if there is an expected delay between the cause and expected effect, then the effect must occur after that delay).

• Dose–response relationship: Greater exposure should generally lead to greater incidence of the effect. or vice versa

• Plausibility: A plausible mechanism between cause and effect is helpful

• Coherence: Coherence between epidemiological and laboratory findings increases the likelihood of an effect.

• Experiment: "Occasionally it is possible to appeal to experimental evidence".

• Analogy: The use of analogies or similarities between the observed association and any other associations.

Simpson’s paradox

effects/trends seen in data from different groups disappears/reverses when groups are combined

PFGE

Pulse-Field Gel Electrophoresis: Its purpose is to separate large DNA fragments of bacterial isolates to generate a “fingerprint” for each strain. This allows epidemiologists to determine whether isolates from different patients or sources are genetically similar.