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z Epidemiology - Cumulative Bitch > Epi MT 4-6 > Flashcards

Epi MT 4-6 Flashcards

1
Q

Epidemiology

  • describes the amount and distribution of disease within a population, regardless of causality
  • IDs who, when, where
  • observational, not experimental
A

Descriptive

-e.g. prevalence of color vision deficiency in boys by ethnicity

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2
Q

Epidemiology

  • concerned with causes and effects of diseases within populations
  • asks why, how
  • association bw exposures and outcomes
A

Analytic
-e.g. diet and AMD: the Melbourne… study - concluded diet high in some things seem to be assoc with advanced AMD prevalence

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3
Q

4 types of descriptive studies in increasing complexity

A

Case report
Case series
Cross sectional
Ecological

(Note alphabetical)

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4
Q

Descriptive studies

  • detailed description of a single case
  • often a unique case
  • cannot generalize, but can initiate studies
A

Case reports

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5
Q

Descriptive studies

  • subjects of common characteristics of a disease
  • no healthy comparison/control group
A

Case series

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6
Q

Descriptive studies

  • examines relationship bw diease and other variables
  • a snapshot of the study population
  • can be done in a relatively short period of time with large populations
A 
Cross sectional (aka prevalence study)
-e.g. ocualar-visual defect and visual neglect in stroke patients
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7
Q

Descriptive studies

  • units of analysis are populations or groups (NOT individuals)
  • aggregate/overall population risk is determined
  • may be done when group, but not individual data is known
A

Ecological studies

-e.g. correlation bw dietary fat intake and breast cancer by country (key = by country, not individual)

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8
Q

Descriptive studies

-describe ecological fallacy

A

Findings from ecological studies may not necessarily be applied to an individual

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9
Q

Analytic studies

  • investigator manipulates 1+ risk factors and analyzes the effeccts
  • can control external factors
  • more expensive and difficult
A

Experimental

-e.g. randomized clinical trial

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10
Q

Analytic studies
-experimental: randomized clinical trial
—used to evaluate __
—generally most __

A 
Eval intervention (preventative or therapeutic procedure)
-evals efficacy and potential harm of intervention

Most scientifically rigorous method

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11
Q

Analytic studies

  • people are observed to see whether there’s a relationship bw risk factor and health status
  • most common design in epidemiology
  • no intervention given
A

Observational

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12
Q

Analytic studies: observational

  • group of ppl with given characteristics followed over time (longitudinal study)
  • may be most important epidemiological study
  • used for diseases that are common
  • good way to eval relationship bw development of disease and risk factor
  • not useful for diseases that take a while to develop & expensive
A

Cohort

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13
Q

Analytic studies: observational
-cohort
—none of the individuals have the disease in the beginning
—follow into the future to observe presence/absence of disease
—compare risk factors
—DIRECT MEASURE OF INCIDENCE AND RISK

A

Prospective

-e.g. Framingham heart study

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14
Q

Analytic studies: observational
-cohort
—IDs individuals with and without the diease in the present
—go back to a time when all of them were free of disease
—compare groups with regard to risk factors
—incidence measured

A

Retrospective

-e.g. statin use and cataract surgery (published 2013, data from 1998-2009)

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15
Q

Analytic studies: observational

  • cases and controls are compared with regard to suspected risk factors for the disease
  • usually small groups, rare conditions
  • inexpensive, no need to follow over time
  • tough to generalize, no new cases/incidence not measured
A

Case-control

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16
Q

Risk quantification

  • probability of an adverse event taking place in a population within a specified time
  • measure of incidence
A

Absolute risk

17
Q

Risk quantification

-how to measure excess risk

A

Relative risk

18
Q

Risk quantification

-equation for relative risk (risk ratio)

A

= (risk in people exposed)/(risk in people not exposed)

19
Q

Risk quantification
-ex: new cls wearer asks what his risk of getting an ulcer is - however, even without CLS, he could get an ulcer, so what he is really asking is ___

A

Excess risk

20
Q

Risk quantification

-ex: smokers’ relative risk of AMD is 3.29. What does this mean?

A

The risk of developing AMD among smokers is 3.29x greater than that of the population of non-smokers (NOT 3.29x greater than overall pop)

21
Q

Risk quantification

-regarding CL wear and corneal ulcers, what does a risk ratio of 3.0 mean?

A

The relative risk of developing (a corneal ulcer) is 3x greater in (CL wearers than non-CL wearers)

22
Q

Risk quantification

-regarding current smokers and AMD, what does a risk ratio/relative risk of 1.26 mean?

A

Current smokers are 1.26xs more likely to develop AMD than non-smokers

I.e. 26% more likely

23
Q

Ratios

-used in cohort, not case-control studies

A

Risk ratio

24
Q

Ratios

-used in case-control, cross-sectional, and cohort studies

A

Odds ratio

25
Q

Ratios

-a comparison of frequency of exposure among cases and controls

A

Odds ratio

26
Q

Odds ratio
= (odds in favor of exposure among cases)/(odds in favor of exposure among controls)
-asks if a patient with a disease is more likely to have a risk factor than a patient without the disease

A

Exposure odds ratio

-asks about the risk factor

27
Q

Odds ratio
= (odds in favor of disease among exposed)/(odds in favor of the disease among unexposed)
-asks if a patient with a risk factor is more likely to have a disease than a patient without

A

Disease odds ratio

-asks about disease

28
Q

Confidence interval

  • used to address the (2) of the results
  • represents the __ of the study
  • usual value
  • depends on (2)
A

Repeatability or variability b/w studies

Precision, more narrow = more precise results

95%

Size of sample and variability

29
Q

Study results and chance

  • chance definition
  • null hypothesis
A

Random error, inherent in all studies
-can be minimized, never eliminated

Idea that there’s no real difference and any statistical differences are due to chance alone
-goal of all studies is to reject it

30
Q

Statistical significance

  • define P value
  • P values that are statistically significant
A

The probabilty that the effect is due to chance alone

SS (rejecting null hypothesis) = P values typically starting at/below 0.05
-means there’s a <5% probability results are due to chance

31
Q

Sampling

  • simple
  • stratified
A

Each person has an equal chance of being selected

Population is divided according to characteristics, then randomly selected from those subgroups

32
Q

Bias

  • selection
  • information
  • confounding
A

S: airsing from selection of individuals

I: each group does not receive the same info
-e.g. multiple interviewers with different styles

C: due to association of other factors that influence the outcome
-e.g. coffee drinkers are commonly smokers, which is the risk for heart disease

33
Q

Confounding bias

-attempts to avoid it

A

Masking - single or double-blind

34
Q

Validity

  • internal
  • external
A

I: extent to which results reflect the relationship bw exposure and outcome

E: generalizability to similar populations

*want good validity, low bias

35
Q

Number needed to treat (NNT)

-why it’s used

A

In clinical trials to put results into perspective

-e.g. you would have to treat 20 pts with OHT to prevent 1 cause of glaucoma developing in 5 years

36
Q

Clinical trial phases (4)

A

1 - small group, safety, dosage range, SE

2 - larger group, efficacy, safety

3 -efficacy, SE, comparison with commonly used treatments

4 - effect in various populations and SE associated with long-term use

z Epidemiology - Cumulative Bitch (2 decks)

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