Cornerstones of epidemiology: Observational Studies and Routine Data

Question 1

List the hierarchy of scientific evidence

Answer 1

Systematic reviews and meta-analysis
Randomised controlled trials
Cohort studies
Case-control studies
Descriptive studies (inc clinical audit)
Case reports/series

Question 2

Give an example of when you would use a cross-sectional study

Answer 2

Accuracy of diagnostic test

Question 3

Give an example of when you would use a cohort study

Answer 3

Prognosis of disease

Question 4

How could you measure the causes and risk factors of diseases

Answer 4

Various non-randomised designs

Question 5

How could you determine the healthcare needs of the population

Answer 5

various, inc ecological (aggregate) studies

Question 6

How could you determine treatment efficacy

Answer 6

Randomised trial

Question 7

Why are observational studies important

Answer 7

They help us find the cause of diseases

Question 8

Where do many observational studies obtain their data from

Answer 8

Routine data

Question 9

What happens as you go up the hierarchy

Answer 9

The data becomes more robust and less prone to confounding and bias, but all are of value

Question 10

Describe descriptive studies

Answer 10

Describe the distribution of factors or disease in relation to:
Person (e.g. age, sex, race, marital status, occupation, lifestyle)
Place (e.g. variation between and within countries/units – CQC does this)
Time (variation over time and season)

Question 11

Why is standardised mortality ratio important

Answer 11

Used for comparing one area with a “standard population”, adjusting for age (often also sex)

Question 12

Describe the standardised mortality ratio

Answer 12

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 (and sex) structure.

Question 13

Describe the types of data used in descriptive studies

Answer 13

Routine e.g. births, deaths
Survey e.g. Health Survey for England
Performance management: Quality and Outcomes Framework for GPs
Other study designs tend to collect their own data

Question 14

What is meant by routine data

Answer 14

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

The Law says that you have to collect them

Question 15

Describe some of the different types of routine data

Answer 15

Healthcare use and outcome data e.g. deaths, hospital admissions, primary care consultations or prescriptions, immunisation uptake
Exposures and health determinant data, e.g., air pollution, crime statistics
Demographic data e.g. census
Geographical data e.g. health authority boundaries, location of GP practices
Health service provision, e.g. bed/staff counts

Question 16

What are the advantages of routine data

Answer 16

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
Can look at time trends as data is available from past years

Question 17

Describe the disadvantages of routine data

Answer 17

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
Need careful interpretation

Question 18

Describe the coding changes

Answer 18

Free text- converted to code- these systems change over time and get updated- careful interpretation required.

Question 19

Describe some health outcome data collected by routine studies

Answer 19

Mortality
Cancer
Notification of infectious diseases
Terminations of pregnancy
Congenital anomalies
Hospital episode statistics
GP data e.g. QOF (see later)
Road Traffic Accidents

Question 20

Describe cross-sectional studies

Answer 20

Useful for health care providers to allocate resources efficiently and plan effective prevention
Provide clues leading to hypotheses which can be tested in analytical studies
Describe status of individuals with respect to absence or presence of both exposure and disease assessed at the same point in time
…but cannot easily distinguish whether exposure preceded disease: chicken or egg?

Question 21

Why don’t cross-sectional studies give you answers

Answer 21

Data only collected and analysed at one period of time, hence you can’t get answers but you can generate hypotheses.

Question 22

Give some examples of cross-sectional studies

Answer 22

Health Survey for England: has core topics each year since 1991 + special topics
Census (last one was 2011)
General Lifestyle Survey (old GHS) since 1971: alcohol, smoking, household size etc
National surveys of NHS patients
NHS staff survey

Question 23

Describe the census

Answer 23

Began in 1801. Every 10 years
Population estimates
Health question
Other health indicators
Unemployment
Ethnicity
Age
Overcrowding

Question 24

Describe vital registration in England and wales

Answer 24

Births, marriages and deaths

Only ask fathers in marriages- needs updating

Question 25

Describe how mortality can be measured

Answer 25

Death certificates
Local registrars of births and deaths
ONS for coding and processing
Produced as routinely published tables
General DH1
By area DH5
By cause DH2 etc
Public Health Mortality Files
Data extracts

Question 26

In 1984, why was there a massive increase in the number of deaths due to senile dementia

Answer 26

Due to coding change- cannot take data at face value

Question 27

Describe cancer registrations

Answer 27

Voluntary notification to local cancer registry: now national system
Also from death certificates
Useful for both incidence and survival information
Increasingly being linked to hospital admissions data and national clinical audits

Question 28

What were the 4 most commonly diagnosed cancers in the UK in 2001

Answer 28

Breast, Lung, Colorectal and prostate

Question 29

List some infectious diseases that require notification

Answer 29

29 notifiable diseases:
Acute encephalitis	Plague	
Acute poliomyelitis	Rabies
Includes food poisoning, meningitis, tuberculosis and plague
Reported by doctors

Question 30

Describe the Quality and Outcomes Framework

Answer 30

Quality and Outcomes Framework (QOF) is a component of the new General Medical Services contract for GPs from April 2004
QOF rewards practices for the provision of quality care, and helps to fund further improvements in the delivery of clinical care
Collected in a national database system: Quality Management Analysis System
Practice-level data are published; being phased out in many areas
Determines how much money GPs have to reinvest in clinical services depending on how well they manage patients with chronic conditions.

Question 31

What is currently happening with the Quality and Outcomes Framework

Answer 31

It is starting to be phased out, but it is still a useful data source.

Question 32

Describe administrative hospitals admissions data

Answer 32

HES (Hospital Episode Statistics) covers all NHS hospitals + Treatment Centres in England
15m records annually + 60m OPD appts + 19m A&E atts
Coding uses ICD10 and OPCS
Data quality still improving
Many uses

Question 33

What is meant by an episode

Answer 33

Finished Consultant Episode - the time spent under the continuous care of a specific consultant

Question 34

What is meant by an admission

Answer 34

a patient’s stay in hospital, so comprises 1+ episodes and/or transfers between hospitals

Question 35

What is meant by multiple episodes

Answer 35

The patient has been seen by different consultants

Question 36

What is meant by observed morbidity and what does it depend on

Answer 36

Health service knows that you’re ill

How the health system is organised influences who observes you to be ill

Question 37

Describe case-control studies

Answer 37

Case-control studies are commonly used in epidemiology
Relatively cheap and quick to conduct
Suitable for studying what might cause rare diseases

Question 38

Describe the study designs of case-control studies

Answer 38

Appropriate control group- those free of the disease
Target group- those with the disease
Move back in time- ask questions about certain exposures, determine odds of exposure.

Question 39

Outline the procedure for carrying out a case-control study

Answer 39

Procedure Example
1 Select cases with disease Cases: brain tumours
controls without disease Controls: from population without cancer

2 Obtain information on past Examine mobile phone exposures and other use to classify people factors into exposure categories

3 Compare proportions of Compare proportion of people exposed in frequent mobile phone cases and controls users in cases and controls

Question 40

Describe the selection of controls

Answer 40

Selection of an appropriate comparison group is the most difficult and critical issue in the design of case-control studies

Controls are subjects free of the disease (or outcome of interest) during the same period of time in which the cases were identified.
They should be representative of the population of individuals who would have been identified and included as cases if they had also developed the disease

Question 41

What are some of the sources of data for controls

Answer 41

General population
Neighbourhood
Friends/relatives
Hospital or clinic-based
These all vary in amount of recall bias, response rates, selection bias, cost

Question 42

How do you calculate an odds ration

Answer 42

Odds of exposure in controls/ odds of exposure in cases

Question 43

What are the advantages of case control studies

Answer 43

Good for rare diseases
Quick and cost-efficient
Can investigate many exposures simultaneously

Question 44

What are the disadvantages of case-control studies

Answer 44

Problems with selection of controls (selection bias)
Subject to recall bias
uncertainty of exposure-disease time relationship
Poor for rare exposures
Cannot calculate incidence rates directly

Question 45

Why are admission criteria sometimes different

Answer 45

They depend on the judgement of each doctor

Question 46

What is meant by a cohort

Answer 46

A “cohort” is a group of people who have something in common:
All patients registered with the same GP
Everybody who has received the swine flu vaccine
People with an allergy to cats
A cohort represents the outcome-free population from which cases (people with the outcome) eventually arise

Question 47

Describe the study design of a cohort study

Answer 47

Exposed and unexposed individuals in outcome-free individuals
Measure those who get the disease in each group
Calculate risk ratio

Question 48

How do you calculate risk ratio

Answer 48

Risk factor of disease in exposure group/ risk factor of disease in unexposed group

Question 49

Describe the advantages of cohort studies

Answer 49

Able to look at multiple outcomes

Able to follow through the natural history of disease

Good design to look at risks related to rare exposures

Incidence can be calculated

Can minimise bias in estimating exposure if prospective

Question 50

Describe the disadvantages of cohort studies

Answer 50

Inefficient for studying rare diseases- you would need 1000s of participants for thorough analysis

Expensive and time consuming (if prospective)

Loss to follow-up may introduce bias

Healthy worker/volunteer effect may affect generalisability

Question 51

Describe the healthy worker effect

Answer 51

Healthier people are more likely to volunteer to participate in cohort studies, hence bias is introduced and the findings are not as representative.