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PPS Epidemiology > CVD > Flashcards

CVD Flashcards

1
Q

Roughly how many deaths is CHD responsible for each year? And what percentage of those are in low income countries?

A
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2
Q

Give a definition of a Cohort study:

A
  • A prospective, cohort study is one in which a*
  • group of people with different exposures is*
  • followed over time to see if they acquire a*
  • disease/outcome.*
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3
Q

What are the strengths and weaknesses of a Cohort Study?

A

Strengths

Strong research design, because exposure is measured before disease develops

Can provide information on several parameters - relative risk, incidence and attributable risk

Can look at several exposures and several disease outcomes in one study

Weaknesses

Not quick or cheap!

Challenging when disease studied is rare

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4
Q

What is the UK incidence of CHD and VTE?

A
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5
Q

What are some notable CHD studies and what were their approximate number of participants?

A
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6
Q

What are some notable confounding factors that could be present in a study of CHD?

A

AGE? SEX?

HIGH BLOOD PRESSURE

CIGARETTE SMOKING

SOCIAL CLASS

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7
Q

Which extra consideration do you need to take into account when deciding on a sample size for at cohort study (as apposed to a CCS)

A
  • What is the incidence rate in unexposed group?
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8
Q

Give examples of particular sections of the general population that can be helpful in selecting your cohort, ensuring a range of exposures?

A

Geographically defined population e.g. Framingham Study

Well defined population groups e.g.

  • General Practice population
  • British doctors
  • Civil servants
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9
Q

Explain what groups you would choose when trying analyse an occupational causes of disease?

A

A highly exposed occupational group

vs a…

Low exposure comparison group e.g.

  • An internal comparison group of workers in the same factory without exposure
  • An external comparison group of similar workers without exposure

In this way, cohort study can study exposures uncommon in general population (difficult in CCS)

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10
Q

What are the considerations in assessing baselines of risk/exposure in cohort studies?

A
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11
Q

Cohort studies allow examination of multiple outcomes if desired, how can the data be collected?

A

Outcome data can come from various sources

  • Routine surveillance systems; death and cancer registers
  • Medical records
  • Questionnaire data
  • Physical re-examination

NB: Outcome data collection should be collected independently of knowledge of exposure

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12
Q

How are incidence rate*, relative risk and attributable risk* calculated in a cohort study

*Only possible in a cohort study (not possible in CSS)

A

See image for explanation, example given below:

Incidence Rates

  • Low total cholesterol (<4 mmol/L) CHD mortality rate 3/1000/year
  • High total cholesterol (>7.5 mmol/L) CHD mortality rate 20/1000/year

Relative risk (high cholesterol) = 20/3 = 6.6 (ratio)

Attributable risk = 20-3 = 17/1000/year (difference)

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13
Q

What is the difference between Logistical Regression and Cox Proportional Hazard Modelling when interpreting the results of a study?

A

Logistic regression takes account of whether an event has occurred during follow-up (0 or 1)

Cox proportional hazards modelling takes account of whether and when incident events occurred, so more precise)

CPHM can take account of graded exposures, and for potential confounding (using stratification and adjustment, similar principles as in case control studies)

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14
Q

Outline the Bradford-Hill Criteria for determining if a positive result is likely to be causal

A
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15
Q

Which of the following are causes, and which are risk factors (some are both)?

Age

Sex

Ethnicity

Family history

High blood pressure

High blood cholesterol

Cigarette smoker

Obesity

Type 2 diabetes

A
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16
Q

What are the main examples of Selection and Information bias present in Cohort studies? And can they be avoided?

A

Selection bias

There is marked and selective loss to follow up

(To be a serious problem this would need to involve subjects with a particular exposure-disease combination (e.g. low cholesterol with high CHD risk)being lost to follow-up)

  • Ensure that follow-up is as complete as possible

Information bias

Misclassification of outcome status (disease or not)

influenced by knowledge of exposure status

  • Ensure that assessment of outcome events is carried out without reference to knowledge of exposure (minimizes information bias)
17
Q

What are the advantages and disadvantages of a cohort study over a CCS?

A

Advantages

  • Exposure is measured before disease onset, reducing potential for bias
  • Allows temporal sequence of exposure and effect to be studied (exposure precedes effect – a key Bradford Hill criterion)
  • Multiple outcomes (diseases) can be studied for many different exposures
  • Incidence of disease can be measured in the exposed and unexposed groups
  • Very large cohorts and/or pooling of data from several cohorts can add statistical power and precision
  • One can even include a…

Nested case control studies within a cohort study

Historical (retrospective) cohort studies

Disadvantages

  • Slow, expensive, administratively difficult and complex
  • Needs large numbers of participants studied over a long time period
  • Difficult to keep study procedures constant over time
  • Changing exposure and diagnostic criteria over time
  • Ascertainment of outcome status may be influenced by knowledge of exposure
  • Losses to follow up may introduce selection bias (i.e. those left have different health behaviours)
  • Collection of data may alter behaviour of participants
18
Q

How can a CCS be nested within a Cohort study?

A

Within a cohort study, once follow-up has occurred, it is possible to do a focussed study in samples of incident disease cases and controls (non-cases) and compare exposures – a powerful prospective case control study design (unlike the usual retrospective CCS)

19
Q

What is a Historical Cohort Study?

A

Historical cohort study – exposures have already occurred and been assessed, cohort established while follow-up is occurring (or has already occurred)

20
Q

What different criteria and needs are favoured by either a cohort study or CSS?

A

PPS Epidemiology (6 decks)

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