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POPHEALTH > study designs 1 > Flashcards

study designs 1 Flashcards

1
Q

descriptive studies

A

look at person, place, time (who, when, where, what)
eg: how much type 2 diabetes is present in the population in 2019?

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2
Q

analytic studies

A

look at association (and causation) between exposures and outcomes
eg: is eating McDonalds associated with having a heart attack

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3
Q

the gate frame

A
  • the graphic approach to epidemiology
  • contains PECOT, population, exposed group, comparison group, outcome and time
  • can be applied to all epidemiological studies
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4
Q

what type of study is a cross sectional studies

A

descriptive, observational type of study

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5
Q

what does cross sectional studies measure

A
  • measure both exposure and/or outcomes at a single point in time (a date, an event, or during a specific period of time eg: in the last month)
  • measures prevalence, the proportion of a defined population who have a disease at a given point in time
    eg: surveys and the census
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6
Q

prevalence equation

A

people with disease at point in time / total population at point in time

prevalence ratio= prevalence in exposed/ prevalence in unexposed

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7
Q

what are cross sectional studies used for

A
  • use them to describe and compare prevalences and generate hypotheses about potential risk factors
  • findings can often only be used for hypothesis generation eg: cavities might of come before high sugar consumption
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8
Q

cross sectional studies strengths and limitations

A

strengths:
- assess multiple exposures and outcomes
- can be used to calculate prevalence, distribution of prevalence in the population, and hypothesis generation
- inexpensive and quick

limitations:
- no temporal sequence (exposure and outcome measure at the same time)
- can’t measure incidence or measures of association
- not good for rare exposures/outcomes
- not good for assessing transient/ variable exposures/ outcomes

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9
Q

what type of study is a ecological study

A

descriptive, observational type of study

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10
Q

ecological studies

A
  • they look at exposures and outcomes across groups (eg: states, countries, regions), not individuals
  • we use ecological studies to compare between populations, assess population level factors in disease and hypothesis generation
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11
Q

ecological strengths and weaknesses

A

strengths:
- assess population lvl exposures (eg: uv light, pollution)
- can be used for hypothesis generation
- inexpensive and easy
limitations:
- ecological fallacy: making assumptions about individuals based on data from the group they belong to
- cannot control for confounding
- cannot show causation

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12
Q

what type of study is a cohort study

A

analytical, observational

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13
Q

steps for a cohort study

A

1) identify a source population
2) recruit a sample population who dont have the outcome of interest
3) assess their exposure level and categorise participants into appropriate group
4) follow up over time and see who develops the outcome
5) calculate your measures of association and occurrence
- so in a cohort study we know the exposure comes before the outcome

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14
Q

occurence equations

A

incidence proportion =
no. of people who developed disease/ no. of people at risk at start of follow up period

incidence rate= no. of people who develop disease/ no. of person years at risk

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15
Q

association equation

A

relative risk= incidence in exposed/ incidence in unexposed

risk difference= incidence in exposed- incidence in unexposed

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16
Q

cohort studies considerations

A

1) healthy worker effect
- when studies are derived only from a population of adult workers this cannot be generalised to the population at large
- this is bc those who are working are overall healthier than those who are not
2) we need to be sure that our sample population doesn’t have the outcome
3) need to ensure our participants have been correctly classified into exposure groups (and haven’t changed exposure groups during the study period)
4) loss to follow up, did any participants leave the study
5) has the outcome been classified correctly

(LOSEH)

17
Q

cohort studies strengths and limitations

A

strengths
- temporal sequence (exposure must precede outcome)
- can look at multiple outcomes
- can calculate measures of association
- good for rare exposures

limitations
- loss to follow up and its associated bias
- potential for exposure/outcome misclassification
- time consuming
- expensive
- not good for rare outcomes

18
Q

types of cohort studies

A

1) prospective cohort studies
- starting when everyone is outcome free and following them up
2) historical cohort studies
- start with the outcome and use existing data to reconstruct the follow up period
- good for outcomes which are rare or take a long time to develop, are less expensive, and less time consuming
- however there could be problems with data qualify, selection bias, or incomplete info

19
Q

limitations of prevalence

A
  1. difficult to assess the development of disease
  2. is influenced by the duration of the disease
20
Q

incidence

A

the occurrence of new cases of an outcome in a population during a specific period of follow up

21
Q

incidence proportion

A

the proportion of an outcome-free population that develops the outcome of interest in a specified time period

22
Q

why might people not be considered ‘at risk’ at the start of a study?

A
  • they already have the condition
  • the condition is something that they cannot develop
23
Q

incidence proportion limitations

A
  • assumes a ‘closed’ population (does not account for people coming or going eg: people might die from something completely unrelated)
  • highly dependent on the time period (longer time period= higher incidence proportion )
24
Q

incidence rate

A

the rate at which new cases of the outcome of interest occur in a population

25
Q

what is person-years at risk

A

sum of everyone in the populations time at risk of becoming a case

26
Q

why might someone stop being ‘at risk’?

A
  • they become a case
  • they are lost to follow up
  • follow up time ends
27
Q

incidence rate limitations

A
  • person time not available
  • complex to calculate
28
Q

PECOT

A

Population- the group of people in the study
Exposure- what the potential determinant is
Comparison- what the potential determinant is being compared to
Outcome- the health outcome being assessed
Time- how long people are being followed up

29
Q

null value in RR

A

exposure doest change occurrence of outcome, so no association between exposure and outcome

30
Q

risk factor in RR

A

greater occurrence of outcome in exposed group, if outcome is bad, exposure is potentially a risk factor for the outcome

31
Q

protective factor in RR

A

greater occurrence of outcome in comparison group, if outcome is bad exposure is potentially a protective factor for the outcome

POPHEALTH (8 decks)

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