7 Observational Studies and Routine Data

Question 1

Q: What is the hierarchy of study design? (7)

Answer 1

A:  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

Q: What are descriptive studies in epidemiology?

Answer 2

A: examine the distribution of disease across various factors including population or sub-groups, geographical location and time period

Question 3

Q: Best study design to determine the accuracy of diagnostic tests?

Answer 3

A: cross- sectional design

Question 4

Q: Best study design to determine disease prognosis.

Answer 4

A: cohort study

Question 5

Q: Best study design to determine the causes and risk factors of a disease?

Answer 5

A: various non-randomised designs

Question 6

Q: Best study design to determine population healthcare needs?

Answer 6

A: various, inc ecological (aggregate) studies

Question 7

Q: Best study design to determine treatment efficiency.

Answer 7

A: randomised trial

Question 8

Q: What data is used in descriptive studies? (3) Where does data come from for other study designs?

Answer 8

A: Types of data used are:
 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 9

Q: List 3 cross sectional survey examples.

Answer 9

A: • 2001 Census
• Health Survey for England
• NHS Inpatient Survey on patient experience

Question 10

Q: What is routine data?

Answer 10

A: 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 11

Q: What are the types of routine data? (8)

Answer 11

A:  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
 Health service provision data e.g. bed staff counts
 Births
 Deaths

Question 12

Q: What are the advantages of routine data? Cost? Availability? Collection procedure? (4)

Answer 12

A: 	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 13

Q: What are the disadvantages of routine data? (5)

Answer 13

A:  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
 Need careful interpretation

Question 14

Q: What are examples of health outcome data? (8)

Answer 14

A: 	Mortality
	Cancer
	Notification of infectious diseases
	Terminations of pregnancy
	Congenital anomalies
	Hospital episode statistics
	GP data e.g. QOF (Quality of Outcomes Framework)
	Road Traffic Accidents

Question 15

Q: Why are cross sectional studies useful? What do they describe? Downfall?

Answer 15

A: useful for health care providers to allocate resources efficiently and plan effective prevention

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 16

Q: What are cancer registrations? Useful for? Linked to? Good data?

Answer 16

A: Voluntary notification to local cancer registry: now national system (Also from death certificates)

both incidence and survival information

Increasingly being linked to hospital admissions data and national clinical audits

Good epidemiological data- allows us to determine most common types of cancer

Question 17

Q: Who reports infectious diseases? Examples of such diseases. (4)

Answer 17

A: doctors

Includes food poisoning, meningitis, tuberculosis and plague

Question 18

Q: What is the quality and outcomes framework (QOF) a component of? Rewards? Collection? Published?

Answer 18

A: component of the new General Medical Services contract for GPs from April 2004

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

Question 19

Q: What is the finished consultant episode?

Answer 19

A: the time spent under the continuous care of a specific consultant

Question 20

Q: What is admission?

Answer 20

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

Question 21

Q: Why are case controls studies good? Suitable for? Requires? What’s compared?

Answer 21

A: Relatively cheap and quick to conduct

studying what might cause rare diseases

cases (with disease) and controls (without disease) and compare those who are exposed and unexposed from each group

You are comparing odd of being exposed among cases and controls

Question 22

Q: What are controls in a case control study? Should be?

Answer 22

A: subjects free of the disease (or outcome of interest) during the same period of time in which the cases were identified

representative of the population of individuals who would have been identified and included as cases if they had also developed the disease

Question 23

Q: What is the most difficult and critical issue in the design of case-control studies?

Answer 23

A: Selection of an appropriate comparison group

Question 24

Q: What are sources of controls? (3) (general population) What do they all vary in? (4)

Answer 24

A:  Neighbourhood
 Friends/relatives (depends on disease)
 Hospital or clinic-based

These all vary in amount of recall bias (getting people to remember things about the past), response rates, selection bias, cost

Question 25

Q: What are the advantages of case control studies? (3)

Answer 25

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

Question 26

Q: What are disadvantages of case control studies? (5)

Answer 26

A:  Problems of selection of controls (Selection bias)  Subject to recall bias  Uncertainty of exposure- disease time relationship  Poor for rare exposures  Cannot calculate incidence rates directly (usually fixed number of controls in sample)

Question 27

Q: What is a cohort? eg? What does it represent?

Answer 27

A: “cohort” is a group of people who have something in common: – All patients registered with the same GP A cohort represents the outcome-free population from which cases (people with the outcome) eventually arise

Question 28

Q: What does a prospective study compare? Looks at? Speed?

Answer 28

A: – Compare rates of disease in the exposed group and unexposed groups. – Thus, looking at outcome after some time has passed slower than retrospective

Question 29

Q: What is a retrospective study usually conducted with? Looks at? Speed?

Answer 29

A: – Done with routine data usually. – Use data to look at the relationship between exposure and outcome. – Quicker way of doing cohort study– Can collect whatever data you like but have to wait a few years to have enough data

Question 30

Q: What are the advantages of cohort studies? (5)

Answer 30

A:  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 31

Q: What are the disadvantages of cohort studies? (4)

Answer 31

A:  Inefficient for studying rare diseases  Expensive and time consuming (if prospective)  Loss to follow-up may introduce bias  Healthy worker/volunteer effect

Question 32

Q: What does the standardised mortality ratio represent?

Answer 32

A:  It 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.  Key confounders such as age may vary between populations. Population death rates may be compared taking into account (or “adjusting”) for the effect of age

Question 33

Q: How is the standardised mortality ratio calculated?

Answer 33

A: number of observed deaths _______________________ number of expected deaths if experienced the same age specific rates as standard population