Use of Data

Question 1

What is the “iceberg of illness”?

Answer 1

Only a small percentage of illnesses are actually reported

Question 2

What is definition of disease?

Definition of illness?

Answer 2

• Disease – symptoms, signs – diagnosis. Bio-medical perspective
• Illness – ideas, concerns, expectations – experience. Patients perspective

Question 3

What factors can affect the uptake of care?

Answer 3

• Lay referral: granny know’s best
• Sources of info: Peers, family, internet TV, health pages of newspaper or women’s mag, “What should I do? Booklet, SHOW website, Practice leaflet or website
• Medical factors: new symptoms, visible symptoms, increasing severity, duration etc
• Non-medical factors: crisis, peer pressure “wife sent me”, patient beliefs, expectations, social class, economics

Question 4

What is the role of epidemiology?

Answer 4

A basis for being able to provide information to advise

• Description
• Explanation
• Disease control

Question 5

How does epidemiology function?

Answer 5

It compares groups (study populations) in order to detect differences pointing to –

• Aetiological clues (what causes the problem)
• The scope for prevention
• The identification of high risk or priority groups in society.

Question 6

What are the fundamental measures within epidemiology?

Answer 6

Epidemiology deals with populations.

It is essential to be quite clear which populations we are talking about when we carry out studies or surveys or formulate hypotheses.

In order to do this we talk in terms of ratios.

• Numerator/demoninator = events
• Numerator: number of events
• Demoninator: population at risk

Question 7

What is incidence?

Answer 7

• is the number of new cases of a disease in a population in a specified period of time

Question 8

What is prevalence?

Answer 8

• is the number of people in a population with a specific disease at a single point in time or in a defined period of time.
• Chronic illnesses may have a low incidence but a high prevalence

Question 9

What is relative risk?

Answer 9

• Measure of the strength of an association between a suspected risk factor and the disease under study.
• RR = incidence of disease in exposed group/incidence of disease in unexposed group

Question 10

What are some sources of epidemiological data?

Answer 10

• Mortality data
• Hospital activity statistics
• Reproductive health statistics
• Cancer statistics
• Accident statistics
• General practice morbidity
• Health and household surveys
• Social security statistics
• Drug misuse databases
• Expenditure data from NHS

Question 11

What is health literacy?

Answer 11

• people having the knowledge, skills, understanding and confidence to use health information, to be active partners in their care, and to navigate health and social care systems.
• increasingly recognised as a significant health concern around the world

Question 12

What is a descriptive study?

Answer 12

• Attempt to describe the amount and distribution of a disease in a given population
• Kind of study does not provide definitive conclusions about disease causation, but may give clues to possible risk factors and candidate aetiologies
• Cheap study
• follow the time, place, person framework
• useful in:

Identifying emerging public health problems through monitoring and surveillance of disease patterns.

Signalling the presence of effects worthy of further investigation.

Question 13

What are the types of analytical study?

Answer 13

Cross sectional

Case control study

Cohort study

Question 14

Analytic study

Explain a cross sectional study:

Answer 14

• In cross-sectional studies, observations are made at a single point in time
• Conclusions are drawn about the relationship between diseases (or other health-related characteristics) and other variables of interest in a defined population.
• A strength of this method is its ability to provide results quickly; however, it is usually impossible to infer causation.

Question 15

Analytical study

Please explain a case control study:

Answer 15

• two groups of people are compared
• a group of individuals who have the disease of interest are identified (cases),

a group of individuals who do not have the disease (controls).

• Data are then gathered on each individual to determine whether or not he or she has been exposed to the suspected aetiological factor(s). The average exposure in the two groups, cases and controls, is compared to identify significant differences, give clues to factors which elevate (or reduce) risk of the disease under investigation.
• Results obtained from case control studies are expressed as ‘odds ratios’ or ‘relative risks’ (see above). Be aware that relative risks are also presented for cohort studies and randomised trials.

Question 16

Analytical studies

Please explain Cohort studies:

Answer 16

• Baseline data on exposure are collected from a group of people who do not have the disease under study. The group is then followed through time until a sufficient number have developed the disease to allow analysis.
• Original group is separated into subgroups according to original exposure status and these subgroups are compared to determine the incidence of disease according to exposure. Cohort studies allow the calculation of cumulative incidence, allowing for differences in follow up time.
• The results are usually expressed as relative risks (see above), with confidence intervals or p values

Question 17

What are trials?

Answer 17

• Experiments used to test ideas about aetiology or to evaluate interventions.
• The “randomised controlled trial” is the definitive method of assessing any new treatment in medicine.

Question 18

How is a randomised control trial carried out?

Answer 18

• Two groups at risk of developing a disease are assembled, a study (intervention) group and a control group.
• An alteration is made to the intervention group (eg, a suspected causative factor is removed or neutralised), whilst no alteration is made to the control group.
• Data on subsequent outcomes (eg, disease incidence) are collected in the same way from both groups, and the relative risk is calculated.
• The aim is to determine whether modification of the factor (removing, reducing or increasing exposure) alters the incidence of the disease.
• In a trial of a new treatment, the underlying design is the same: the intervention group receive the new therapy, the control group receive the current standard therapy (or a placebo) and the treatment outcomes (eg, reduction in symptoms) are compared in the two groups

Question 19

Interpretating results

What is standardisation?

Answer 19

Set of techniques used to remove (or adjust for) the effects of differences in age or other confounding variables, when comparing two or more populations

Question 20

Interpreting results

What is a standardised mortality ratio?

Answer 20

Special kind of standardisation which you may encounter in your reading. It is simply a standardised death rate converted into a ratio for easy comparison

Question 21

Interpreting data

What is case definition?

Answer 21

The purpose of case definition is to decide whether an individual has the condition of interest or not. It is important in because not all doctors or investigators mean the same thing when they use medical terms.

Question 22

Interpreting data

What is coding and classification?

Answer 22

This is related to the issue of case definition. When data are being collected routinely (eg, death certificates), it is normal to convert disease information to a set of codes, to assist in data storage and analysis. Rules are drawn up to dictate how clinical information is converted to a code. If these rules change, it sometimes appears that a disease has become more common, or less common, when in fact it has just been coded under a new heading.

Question 23

Interpreting data

What is relevence of ascertainment?

Answer 23

Is the data complete - are any subjects missing? If researchers in one country look harder for cases of a given disease than researchers in any other, it might not be surprising that they come up with higher incidence rates.

Question 24

What is Bias and what are the different types of bias?

Answer 24

Any trend in the collection, analysis, interpretation, publication or review of data that can lead to conclusions that are systematically different from the truth

Selection bias:

• When study sample is not truly representative of a whole population

Information bias:

• arises from systematic errors in measuring exposure or disease. For example, in a case control study, a researcher who was aware of whether the patient being interviewed was a ‘case’ or a ‘control’

Follow up bias:

• arises when one group of subjects is followed up more assiduously than another to measure disease incidence or other relevant outcome.

Systematic error:

• A form of measurement bias where there is a tendency for measurements to always fall on one side of the true value

Question 25

What is a confounding factor?

Answer 25

• One which is associated independently with both the disease and with the exposure under investigation and so distorts the relationship between the exposure and disease
• Age, sex and social class are common confounders.

Question 26

What is necessary for Audits?

Answer 26

• A set criteria
• Standards to measure