Epidemiology - Tutorial 1 Flashcards
What is epidemiology?
- study of changing patterns of disease with the aim of improving the health of the population
- looks at the time, place and person affected
What can epidemiological information be used for?
- assisting in making a diagnosis
- assess which services are required for prevention, diagnosis, primary care, secondary care and rehabilitation
- ensure a high quality of these services
- carry out healthcare needs assessments to provide a rational framework for decisions on prioritisation of healthcare resources
What use does epidemiology have by comparing groups?
- detect etiological cues
- decide the scope for intervention
- identify high risk groups
What are 10 sources of epidemiological data?
- mortality data
- hospital activity statistics
- reproductive health statistics
- cancer statistics
- accident statistics
- GP morbidity
- health and household surveys
- social security statistics
- drug misuse databases
- expenditure data from the NHS
What are the 3 aims of epidemiology?
- description - amount, numbers, distribution
- explanation- natural history, cause, high risk groups
- disease control - advice eon treatments and prevention
What is meant by ‘incidence’?
- the number of new cases of disease in a population in a specified period of time
- tells us about causation and aetiology
What is meant by ‘prevalence’?
number of people in a population with a specific disease at a single point in time or in a defined period
What is an example of a high incidence, low prevalence disease?
motor neuron disease
What is an example of a low incidence, low prevalence disease?
Ebola
What is an example of a high incidence, high prevalence disease?
winter flu
How is the relationship between incidence and prevalence affected?
by the duration of the disease - prevalence can only change upon cure or death
What is relative risk?
measure of strength of association between a risk factor and the disease under study i.e. risk of event relevant to exposure
measure of disease in exposed group/measure of disease in unexposed group
What is absolute risk?
probability of harm occurring as a result of a specific risk factor
What are 4 different types of study?
- trials (double-blind, placebo-controlled,RCT)
- surveys
- case-control studies (retrospective)
- cohort studies (prospective)
What do descriptive studies do?
- attempt to describe the amount and distribution of a disease in a given population, for the purposes of gaining insight into the aetiology of the condition or for planning health services to meet the clinical need
- studies may look at the disease alone or may also examine one or more factors (exposures) thought to be linked to the aetiology
- does not provide definitive conclusions about disease causation, but may give clues to possible risk factors and aetiologies
- usually cheap, quick and give a valuable initial overview of a problem
What are descriptive studies useful for?
- finding emerging public health problems through monitoring and surveillance of disease patterns
- signalling the presence of effects worthy of further investigation (flagging up)
- assessing the effectiveness of current measures of prevention and control
- assessing needs for health services and service planning
- generating hypotheses about aetiology
What happens in a cross-sectional study?
- observations are made at one point in time
- able to provide results quickly but impossible to infer causation
What happens in case-control studies?
- two groups of people are compared e.g. with and without disease
- data is then gathered on each individual to determine whether they have been exposed to the suspected etiological factors
- the average exposure in the 2 groups, cases and controls, is compared.
- if there is a significant difference then it can give clues to factors which elevate the risk of the disease under investigation
- results expressed as ‘odds ratios’ or ‘relative risks’
What happens in cohort studies?
- 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
- the 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
- longitudinal, observational study
- analysis of risk factors’ and follows a group of people who do not have a disease under question, and uses correlations to determine the absolute risk
Why are cohort studies better than case control studies?
issues relating to time can be established in a prospective study like short, and confounders are more easy to control for
What happens in a randomised control trial?
- examines two groups at risk of developing a disease (a study group and a control group)
- the study group has a suspected causative factor to the disease neutralised whereas the control group does not
- data on subsequent outcomes are collected in the same way from both groups
- the aim is to determine whether the modification of the factor alters the incidence if the disease
What are 3 challenges for researches in RCTs?
- how to reduce the effect of the result occurring by chance
- how to account for biological variation
- how to ensure that the only difference between the groups is the intervention in the research study
What are 5 features of a randomised control trial?
- an appropriate sample of representative study population
- participants are allocated randomly to each treatment group
- possesses a double-blind design
- there is an objective measure of outcome
- the follow up of participants is complete
What kind of study is deemed the ‘gold standard’ for testing the benefits of one treatment against another?
double blind randomised control trial
What are disadvantages of randomised control trials?
- costly and time consuming
- recruits may not be typical patients (selection bias)
- cannot address all research questions
- limited to people who consent to take part and do not have exclusion criteria
- may lead to false negative conclusions
What is standardisation?
a set of techniques used to remove the effects if differences in age or other confounding variable, when comparing two or more populations
What is a standardised mortality ratio?
special kind of standardisation which is simply a standardised death rate converted in to a ratio for easy comparison
What problems can occur with data?
- quality - is the data trustworthy?
- case definition - do doctors mean the same thing when they call a patient a ‘case’ in a disease?
- coding and classification - ICD-10, DSM?etc or have you used the right code within your system?
What is bias?
any trend in the collection, analysis, interpretation, publication or review of data that can lead to conclusions that are systematically different from the truth
What is selection bias?
when the study sample is not truly representative of the whole study population about which conclusions are drawn
What is information bias?
arises from systematic errors in measuring exposure or disease e.g. researcher being aware of who is a case or a control in an interview with a patient in a case control study
What is follow up bias?
arises when one group of subjects is followed up more assiduously than another to measure disease or outcomes
What is systematic error?
- a form of measurement bias where there is a tendency for measurements to always fall one side of the true value
- e.g. instrument calibrated wrong
What is a confounding factor?
one which is associated independently with both the disease and with the exposure under investigation and so distorts the relationship between the exposure and the disease
How can we alter study design to control for confounders?
- randomisation in trials
- restriction of eligibility criteria to only certain kinds of study subjects
- subjects in different groups can be matched for likely confounding factors
- results can be stratified according to the confounding factors
- results can be adjusted to take account of suspected confounding factors
How can we decide if there is causation between an exposure and a disease? (9)
- strength of association (relative risks or odds ratios)
- consistency - repeated observation of an association in different populations under different circumstances
- specificity - a single exposure leading to a single disease
- temporality - the exposure comes before the disease
- biological gradient - dose response relationship. As exposure increases, so does the risk of the disease.
- biological plausibility- the association agrees with what is known about the disease’s biology
- coherence- the association does not conflict with what is known about the disease’s biology
- analogy - another exposure-disease relationship exists which can act as a model for the one under investigation
- experiment: a suitably controlled experiment to prove the association as causal
What is the only ABSOLUTE criterion for determining causality?
temporality - the exposure must come before the disease
What is an audit?
a quality improvement process that seeks to improve patient care and outcomes by measuring these against explicit criteria and then implementing changes
What are 5 reasons for audits?
- where national standards and guidelines exist; where there is conclusive evidence about effective clinical practice (i.e. evidence based medicine).
- areas where problems have been encountered in practice.
- what patients & public have recommended that be looked at.
- where there is a clear potential for improving service delivery.
- areas of high volume, high risk or high cost, in which improvements can be made.
List the hierarchies of evidence (least biased at top, most biased at bottom).
- systematic review of RCTs with or without meta-analyses
- RCT
- cohort studies
- case-control studies
- case series
- case reports
- opinion
