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Epidemiology > Epidemiology > Flashcards

Epidemiology Flashcards

1
Q

what is prevalence

A

the number of existing cases in a population at a designated time

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2
Q

what is incidence

A

the number of new cases

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3
Q

relationship between prevalence and incidence

A

prevalence = incidence x average disease duration

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4
Q

name the three types of population pyramid

A

-spike - high birth rate, high death rate
-wedge - high birth rate, low death rate, high growth rate
-barrel - low birth rate, low death rate

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5
Q

what is infant mortality rate

A

no. of deaths of infants aged 0-1years/no. live births

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6
Q

what is a total period fertility rate (TPFR)

A

the average number of children that would be born to a woman over her lifetime

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7
Q

define life expectancy

A

the number of years a baby born today can be expected to live if it experienced the current age-specific mortality rates

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8
Q

what is healthy life expectancy

A

expected years of life in good or fairly good general health

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9
Q

what is the PYLL index

A

potential years of life lost
-a measure of the relative impact of various diseases and lethal forces on society
(the number of years of life lost when a person dies prematurely)

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10
Q

what is dependency ratio

A

a demographic measure of the ratio of the number of dependents to the total working age population in a country or region

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11
Q

how do you calculate dependency ratio

A

under 15 plus over 65 years/population ages 15-64 years

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12
Q

what’s a cross sectional study

A

estimate frequency or outcome at a particular point in time
-descriptive or analytical

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13
Q

why do a cross sectional study?

A

-health service planning - prevalence of specific outcome in a defined population at a point in time
-useful for assessing burden of disease and planning preventative and curative services
-not useful for rare diseases
-generate hypotheses about causes
(these studies prove association not causation)

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14
Q

survey sampling

A

-can make statements about the population by asking a (small) sample
-a well taken sample is (almost) as informative as a complete census
-sampling is a feature of all research designs

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15
Q

what is simple random sampling

A

-list the group
-generate random numbers
-contact selected individuals
-collect data

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16
Q

what bias in cross-sectional studies

A

-selection bias (characteristics of those taking part vs those not taking part)
-information bias (recall bias)

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17
Q

advantages of cross sectional

A

-easy and economical
-provides important information on the distribution and burden of exposures and outcomes - health service planning
-can be used as the first step in the study of a possible exposure-outcome relationship

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18
Q

weaknesses of cross sectional

A

-limited value for investigating aetiological relationships
-can be difficult to establish the time-sequence of events, the exposure may have occurred as a result of the outcome (reverse causality)
-not good for rare diseases
-selection bias (characteristics of those taking part/not taking part)
-recall bias
-could generate hypotheses about causes

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19
Q

what is an ecological study

A

observational study with populations or groups (instead of individuals) being unit of observation

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20
Q

what are the uses of an ecological study

A

-described association at group level
-quick and cheap - routine data
-generates hypotheses - first step
-some risk factors may not easily be measurable at an individual level

21
Q

what is ecological fallacy

A

-ecological studies enable us to make ecological inferences about effects at the group-level
-they do not enable us to make inferences about individual risks
-an attempt to infer from the ecological level to the individual level is often called an ecological fallacy

22
Q

purpose of randomised control trials

A

-minimise selection bias
-minimise confounding
-if participants are blind to treatment allocation then reporting bias is minimised
-if investigators are blind to allocation then observer bias is minimised
-provides powerful evidence of a causal relationship between the intervention and the outcome

23
Q

what is incidence risk

A

the number of new cases in interval/population initially at risk

24
Q

what is incidence rate

A

the number of new cases/total person-time at risk

25
Q

what is incidence rate good for

A

dynamic populations

26
Q

what is incidence risk good for

A

static populations

27
Q

what is annual incidence

A

counts the deaths over a calendar year

28
Q

what is cumulative incidence

A

frequency of new cases over a specified period

29
Q

what to consider when deciding if risk factor and disease is causal (10 marks)

A

-consider relative risk, hazard ratio and odds ratio to determine strength of association
-attributable risk
-define causation and association
-consider that aetiology of chronic disease is often difficult to determine
-some exposures may cause more than one outcome
-outcomes may be due to multiple exposures or continual exposure over time
-causes may differ by individual
-probabilistic causation is when causal factor increases the chance of disease
-a sufficient cause is a complete causal mechanism that always produces disease

30
Q

case control main features, advantages and disadvantages (10 marks)

A

-measure exposure in cases vs controls
-select (diseased) cases and (undiseased) controls
-use odds ratio to interpret results
-selection bias can occur as people who participate are only those who are eligible
-observer bias can occur if knowledge of case/control status
-same with participant bias
-there can be rare outcomes
-time varying exposures
-can assess multiple exposures
-there wouldn’t be any recall bias
-can prove a good causal relationship between exposure and outcome

31
Q

advantages of case-control studies

A

-no recall bias
-can show rare outcomes (from rare diseases)
-can look at multiple exposures/risk factors simultaneously
-time varying exposures
-quick, inexpensive and easy
-useful initial studies to establish an association

32
Q

ecological fallacy 6 marker

A

-can happen in ecological studies
-define ecological studies
-ecological fallacy occurs when a researcher attempts to infer from the ecological level to the individual level
-ecological studies do not enable us to make inferences about individual risks
-there are complex associations between disease and exposure
-countries with high or low exposure differ systematically in many other ways

33
Q

what does it mean if p<0.05

A

reject chance
-conclude real effect

34
Q

what does it mean if p>0.05

A

cannot exclude chance
-cannot conclude there is real effect

35
Q

advantages of randomised control trials

A

-minimises selection bias and confounding
-if participant blind to allocation then minimises reporter bias
-if observer blind to allocation then minimises observer bias
-multiple outcomes can be examined
-incidence rate of outcome can be measured

36
Q

disadvantages of randomised control trials

A

-very time consuming - trials can take years
-recruitment is difficult and time consuming
-impossible to do interventional trials sometimes
-expensive

37
Q

advantages of cohort studies

A

-temporality - exposure status defined before outcome
-can measure multiple outcomes from rare exposures
-no recall bias
-its possible to estimate all measures of incidence and effect

37
Q

disadvantages of cohort studies

A

-huge investment of time, human resources and financial resources
-reproducibility is hard
-loss to follow up - bias can be introduced which is difficult to control
-requires large sample size
-uncontrolled confounding variables
-inefficient for rare diseases

38
Q

two types of information bias

A

reporter and observer

39
Q

reporting bias

A

-when subjects give an answer they think will please the investigator
-when subjects conceal potentially embarrassing info
-when subject with a specific health outcome report previous exposure with a different degree of accuracy to other subjects
-when subject who have experienced a specific exposure report subsequent health events to a different degree of accuracy to others

40
Q

how can you avoid/minimise reporting bias

A

-use exposure data before outcome
-objective data sources where possible
-keep subjects unaware of association under study

41
Q

what is observer bias

A

-when accuracy of exposure data recorded by investigator differs (case control and cross sectional)
-when accuracy of outcome data differs (cohort and intervention studies)
-interviewer bias

42
Q

how do you avoid/minimise observer bias?

A

-the people who are responsible for classifying the outcome do not know the subjects’ exposure category
-blinding

43
Q

intention to treat

A

-compares outcomes for all randomised individuals (even if they stop taking treatment or drop out of study)
-assesses the overall effect of assigning a subject to receive a particular intervention
-analysis is the most important analysis as intervention and control groups compared as originally randomised
-more likely to underestimate treatment effect
(in randomised control trials lecture)

44
Q

short notes on incidence risk and rate (6 marks)

A

-incidence measures number of new cases in a group/population
-incidence risk is number of new cases in an interval/population initially at risk
-incidence risk is good for static populations
-incidence rate is number of new cases /total person-time at risk
-incidence rate measures the rate at which a new disease occured over a period of time
-incidence rate is good for dynamic populations
-annual incidence counts deaths over a calendar year
-cumulative incidence is the frequency of new cases over a specified period

45
Q

Cluster sampling

6 mark short notes

A

-cluster sampling involves dividing a population into clusters and then randomly selecting a sample of these clusters
-clusters are randomised
-there must be a lot of clusters to randomise to avoid unequal distribution
-need increased sample size of individuals
-subjects within a cluster may be different to subjects in other clusters so ideal is lots of small clusters
-analysis more complicated as need to take account of cluster design
-allocation concealment more difficult

46
Q

sampling frame

6 mark short notes (only have 4 points rn)

A

-a sampling frame is a list of all the people forming a population from which a sample is taken
-simple random sampling is when people in the group are allocated random numbers
-the sampling frame comes from an initial group of interest from which individuals are selected
-convenience samples are taken from a place that is convenient for that study

47
Q

SMR

short notes

A

-standard mortality ratio
-a measure, expressed as either a ratio or percentage to quantify an increase or decrease in mortality in a study cohort compared to the general population
-calculated from expected deaths in a study population
-compares observed deaths with expected deaths
-needs number of persons in each age group in population being studied
-age specific death rates of general population by same age groups
-observed deaths in study population

Epidemiology (1 decks)

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