6 - Cornerstones of epidemiology

Question 1

Hierarchy of study design

Answer 1

Systematic reviews and meta-analyses (highest – but can still be inadequate)
Randomised Controlled Trials
Cohort studies
Case-control studies
Ecological studies
Descriptive/cross-sectional studies
Case report/series (lowest – but can still be valuable)

Question 2

what do descriptive studies in epidemiology examine

Answer 2

distribution of disease across various factors including population or subgroups, geographical location and time period

Question 3

routine data

Answer 3

Data that are routinely collected and recorded in an ongoing systematic way, often for administrative or statutory purposes and without any specific research question in mind at the time of collection

Question 4

types of routine data

Answer 4

*Health outcome data, e.g. deaths, hospital admissions and primary care consultations or prescriptions, levels of well-being from national surveys
*Exposures and health determinant data, e.g. smoking, air pollution, crime statistics
Disease prevention data, e.g. screening and immunisation uptake
*Demographic data, e.g. census population counts
*Geographical data, e.g. health authority boundaries, location of GP practices
Births
Deaths
Cancer registrations
Notifications of infectious diseases
Terminations of pregnancy
Congenital anomalies
Hospital admissions
Community systems
GP consultation data
Prescriptions
Road Traffic Accidents
* = most important ones in UK

Question 5

Advantages of routine data

Answer 5

Relatively cheap
Already collected and available
Standardised collection procedures
Relatively comprehensive – population coverage, large numbers 
Wide range of recorded items
Available for past years
Experience in use and interpretation

Question 6

Disadvantages of routine data

Answer 6

May not answer the question (no information or not enough detail)
Incomplete ascertainment (not every case captured)
Variable quality (e.g. variable diagnosis fields)
Validity may be variable (i.e. do they measure what you think they
measure?)
Disease labelling may vary over time or by area
Coding changes may create artefactual increases or decreases in rates, e.g. ICD9 to ICD10(ICD=International classification of diseases)
Need careful interpretation

Question 7

Standardised Mortality Ration (SMR)

Answer 7

represents the ratio of the number of observed deaths (or cases of disease) (O) in a particular population to the number that would be expected (E), if that population had the same mortality or morbidity experience as a standard population, corrected for differences in age structure
method for comparing rates
a rate ratio adjusted for age
common for SMRs to be adjusted for age and for sex

Question 8

SMR Equation

Answer 8

number of observed death / number of expected death if experienced the same age-specific rates as standard population