LifeScience 2A03 Tutorial 2

Cross sectional - carried out at one time point or over a short period usually conducted to
estimate the prevalence of the outcome of interest for a given population

  • public health planning

  • investigate associations between risk factors and the outcome of interest

  • They are limited by the fact that they are carried out at one time point and give no indication of the sequence of events

  • The sample used in a large cross -sectional study is often taken from the whole population.

  • Non-response and biased response is an issue

Cohort Studies - is one in which a group of subjects, selected to represent the population of interest, is studied over time

  • Advantages: - The temporal dimension, whereby exposure is seen to occur before outcome,
    gives some indication of causality- Can be used to study more than one
    outcome

  • Disadvantages: Costly (less so for retrospective) and may take a long time, particularly where onset of the outcome measure can occur both early and late on in life
    • Require accurate records for retrospective
    studies
    • When studying rare outcomes, a very
    large sample size is required
    • Prone to dropout
    • Changes in aetiology of disease over time
    may be hard to disentangle from changes
    observed as age increases
    • Selection bias: a difference in incidence
    of the outcome of interest, between those
    who participated and those who did not,
    would give biased results

Prospective studies - studies carried out from the present time into the future

  • can be expensive to carry out due to length

  • high rates of drop out

Retrospective/historical cohort - studies look at medical events from some timepoint in the past up to the present time.

  • advantage of historical cohort studies is that the information is available immediately.

  • is more commonly used because accurate and complete data

Case control studies - to establish association between exposure to risk factors and disease

  • Advantages : Case-control studies are quick and cheap and are particularly suited to the study of rare diseases as the diseased are selected at the outset of the study

  • Disadvantages:
    • difficulties in overcoming potential bias and confounding
    • the successful selection of both cases and controls who are representative of their respective populations is often difficult.
    • an inability to infer causality and no information on the chronology of disease and exposure.
    • Inefficient in studying risk factors which are rare
    • Studies are often not population based, therefore it is impossible to calculate incidence of disease

Analytical - attempt to study and/or quantify the relationship between two or more factors - to explain why something is happening

  • prospective : researcher e