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Flashcards in Epi Deck (38)
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Infectious disease epidemiologic triad

Agent, environment, host

Characteristics:
virulence, pathogenicity, infectivity
Weather, geography, crowding, food
Age, sex, nutrition

1

Reproductive number

R0=B*c*d

probability of transmission
Avg number of contacts per unit time
Avg duration of infectiousness

Rt=bcd*proportion susceptible

2

Epidemic curve

Distribution of disease by time of onset

3

incubation period

Time of infection to time of onset of symptoms

4

Latency period

Time of infection to time of infectiousness

5

Herd immunity

Resistance of a group to infection

6

Type I error

Finding an association when there is none ALPHA

7

Type II error

Finding no association when there is BETA

8

Power

1 - Beta, Correctly finding an association when there is an association, usually 80%

9

Error of concern when confidence level is close to null value

Random error or lack of precision

10

What does wide or narrow CI tell you?

Sample size

11

95% Confidence Interval

When a study has been repeated 100 times, 95% of the time, the CI would contain the real population measure of interest

12

Epidemiology

The study of the distribution and determinants of disease frequency in the human population and the application of the study to control health problems

13

Types of variables

Categorical/nominal, ordinal, continuous

14

Decreasing prevalence means...

More people are cured
More people died

15

Morbidity vs Mortality monitoring

- early id of problem
- but more events to track, spectrum of disease, difficult to ID and count, Less complete
- Fewer events to track, ID impt health problems, very complete
- but Far downstream in the disease process, tip of iceberg, cause of disease misclassification

16

Case Fatality Rate

Number of people who die from disease within the people who have the disease, expression as per 100,000 population

17

Annual Mortality Rate

number of deaths in the year over population at mid year, expressed as percentage

18

Case Reports and Case series: impt and limitations

Importance: Early detection of unusual occurrence, preliminary source of information for potential
Limitations: No comparison group, Small sample size, no exposure collected

19

Observational vs Experimental Studies

- Exposure is assigned in experimental, assignment is randomized, maximize control, expensive and maybe unethical

20

Descriptive vs analytic studies

Descriptive: burden and patterns, no direct inference to causality, first impt clues about causes
Analytic: hypothesis stated and tested, associations betwee E and D to understand cause

21

Name some descriptive studies

cross sectional, case series, case report

22

Cross-sectional studies

snapshot, planning, but no temporal order, NHANES

23

Purpose of surveillance

est magnitude of problem, geographic distribution, detect epidemics, evaluate control measures, monitor infectious agents, detect changes in health practice, facilitate planning

24

Pearson's correlation

parametric (outcome is continuous and normally distributed)

25

Spearman r

non-parametric,discrete, ordered

26

Instrumental Variable, mendelian randomization studies

predictors of exposure like genes

27

Attack rate

# sick / # exposure to agent

28

3 Biases

Selection Bias, Information bias, confounder

29

How to adjust for measurement error?

blinding, triangulate, validated measures

30

How to adjust for confounder?

randomization, instrumental variable, matching, restriction at design stage
weighted average, propensity score, multivariate analysis at analysis stage

31

Selection bias

selecting participants not independent of exposure OR loss to f/u at different rates

32

Confounding definition

Unequal distribution of another cause of disease between exposed and unexposed

33

Koch's POstulates

microorganism must be found in all suffering
must be isolated and grown in pure culture
should cause disease when introduce to healthy organism
reisolated from the inoculated, and ID as being identical to the original agent

34

Hill and Doll

Cigarette smoking

35

Hill's causal viewpoints

- strength of assc
- consistency
- specificity
- time sequence
- biological gradient
- plausibility
- coherence
- experimental
- analogy

36

dose response, biological gradient

dose response, threshold effect, ceiling effect

37

Association and causation

assoc - being able to predict one based on the other
causation - without one, the disease may not happen or will happen at a later time