Why is data gathered?
So that we can communicate risk to patients
What does data about illness allow us to determine?
Treatment plans
What are guidelines such as SIGN based on?
Data, known as the “hierarchy of evidence”
What does general practice act as?
The interface between the public and secondary care (hospital)
What percentage of general practice consultations are referred onto hospital investigation or care?
3%
Most illnesses are unreported, what is this known as?
Iceberg of illness
What is a disease?
Disorder of structure or function
What is an illness?
Disease or period of sickness affecting the body or mind
What are some factors affecting the uptake of care?
- Concept of lay referral
- “Granny knows best”
- Sources of info
- Peers, family, internet
- Medical factors
- New symptoms, visible symptoms, increasing severity, duration etc
- Non-medical factors
- Crises, peer pressure, “wife sent me”, patient beliefs, expectations, social class, economic, psychological, environment, cultural, ethnic, age, gender, media etc
What are some medical factors that impact the uptake of care?
- New symptoms, visible symptoms, increasing severity, duration etc
What are some non-medical factors affecting the uptake of care?
- Crises, peer pressure, “wife sent me”, patient beliefs, expectations, social class, economic, psychological, environment, cultural, ethnic, age, gender, media etc
What are the different categories of illnesses?
Acute, chronic or self-limiting
Do more males or females see their GP?
More females see their GPs than males, until over 65s
What are some possible issues from the patients POV about accepting they have an illness?
- Believes themselves to be healthy
- Is physically fit
- Proud to not be using tablets
- If treatment is proposed, how would he feel better
What is epidemiology?
The branch of medicine which deals with incidence, distribution and possible control of disease and other factors relating to health
What are the 3 main aims of epidemiology?
- Description
- To describe the amount and distribution of disease in human populations
- Explanation
- To elucidate the natural history and identify aetiological factors for disease usually by combining epidemiological data with data from other disciplines such as biochemistry, occupational health and genetics
- Disease control
- To provide the basis on which preventative measures, public health practices and therapeutic strategies can be developed, implemented, monitored and evaluated for the purposes of disease control
What does description mean in terms of epidemiology?
- To describe the amount and distribution of disease in human populations
What does explanation mean in terms of epidemiology?
- To elucidate the natural history and identify aetiological factors for disease usually by combining epidemiological data with data from other disciplines such as biochemistry, occupational health and genetics
What does disease control mean in terms of epidemiology?
- To provide the basis on which preventative measures, public health practices and therapeutic strategies can be developed, implemented, monitored and evaluated for the purposes of disease control
Epidemiology compares groups (study populations) in order to detect differences pointing to what?
- Aetiological clues
- Scope for prevention
- Identification of high risk or priority groups in society
What are examples of things that can define a study population?
Age
Sex
Location
What is a fundamental difference between clinical medicine and epidemiology?
Clinical medicine deals with individual patient
Epidemiology deals with populations
What is done to be clear about which populations we are talking about when we carry out studies?
We talk about ratios:
- Number of events/population at risk
- Such as deaths from IHD in men aged 55-63 in Grampian in 1990/all men aged 55-64 in Grampian in 1990
- Ratios are usually converted into rates by expressing them in terms of a specified time period (per year) and a notional ‘at risk’ population of 10n (eg % per 1000 or per 100000)
What is incidence?
Number of new cases of a disease in a population specified period of time
What does incidence and prevalence tell us about?
Incidence tells us something about the trends in causation and the aetiology of disease
Prevalence tells us something about the amount of disease in a population
What is prevalence?
Number of people in a population with a specific disease at a single point in time or in a defined period of time
What is relative risk?
Measure of the strength of an association between a suspected risk factor and the disease under study
What does RR stand for?
Relative risk
What formula describes relative risk?
What is absolute risk?
Absolute risk is the probability of an event happening, number of events that occurred in a group divided by the number of people in that group, this is also known as actual risk
What is absolute risk also known as?
Actual risk
What are examples of sources of epidemiological data?
- Mortality data
- Hospital and clinical activity statistics
- Reproductive health statistics
- Infectious disease statistics
- Cancer statistics
What is health literacy about?
Is about 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
What are SIGN guidelines based on?
Based on systematic review of the scientific literature and aimed at aiding the translation of new knowledge into action
What are SIGN guidelines intended to do?
- Help health and social care professionals and patients understand medical evidence and use it to make decision about healthcare
- Reduce unwarranted variations in practice and make sure patients get the best care available, no matter where they live
- Improve healthcare across Scotland by focusing on patient important outcomes
What are different classes of study types?
Descriptive studies
Analytical studies
Cohort studies
Trials
What are descriptive studies useful for?
- Identifying emerging public health problems through monitoring and surveillance of disease patterns
- Signalling the presence of effects worthy of further investigation
- Assessing the effectiveness of measures of prevention and control (such as screening programmes)
- Assessing needs for health services and service planning
- Generating hypotheses about disease aetiology
What do descriptive studies attempt to do?
- Attempt to describe the amount and distribution of a disease in a given population
What does descriptive studies not provide?
- Does not provide definitive conclusions about disease causation but gives clues to possible risk factors (exposures) linked to candidate aetiology
What are advantages of descriptive studies?
- Usually cheap, quick and give a valuable initial overview of a problem
What are different kinds of analytical studies?
- Cross sectional study
- Looks at disease frequency, survey, prevalence study)
- 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
- Strength is delivers results quickly, usually impossible to infer causation though
- Case control study
- Two groups of people are compared
- Group of individuals who have the disease of interest (cases)
- Group of individuals who do not have the disease (controls)
- Results are expressed as odds ratios or relative risk
- Confidence intervals or ‘p values’ are presented as a guide as to whether the results could be a chance finding
- Two groups of people are compared
What do cross sectional studies look at?
- Looks at disease frequency, survey, prevalence study
In cross sectional study are observations made at a single point of time or longitudinal?
Single point of time
Cross sectional studies draw conclusions about what?
- Conclusions are drawn about the relationship between diseases (or other health-related characteristics) and other variables of interest in a defined population
What are advantages of cross sectional studies?
- Strength is delivers results quickly, usually impossible to infer causation though
What are case control studies?
- Two groups of people are compared
- Group of individuals who have the disease of interest (cases)
- Group of individuals who do not have the disease (controls)
What are the results of case control studies expressed as?
- Results are expressed as odds ratios or relative risk
- Confidence intervals or ‘p values’ are presented as a guide as to whether the results could be a chance finding
What do confidence intervals or ‘p values’ indicate?
Whether the results could be a chance finding
What happens in cohort studies?
- Baseline data on exposure are collected from a group of people who do not have the disease under study
- Followed through time until a sufficient number have developed the disease to allow analysis
- Allows calculation of cumulative incidence, allowing for differences in follow up time
- Results are expressed as relative risks
What do cohort studies allow for the calculation of?
- Allows calculation of cumulative incidence, allowing for differences in follow up time
What are the results of cohort studies expressed as?
- Results are expressed as relative risks
What are trials?
- Experiments used to test ideas about aetiology or to evaluate interventions
What is the definitive method of assessing any new treatment in medicine?
Randomised conrol trial
What happens in a randomised control trial?
- Two groups at risk of developing a disease are assembled, a study (intervention) group and a control group
- Alteration made to intervention group (such as suspected causation factor neutralised) whilst no alteration is made to the control group
- Data on subsequent outcomes (such as disease incidence) are collected in the same way for both groups, and the relative risk is calculated
- Aim is to determine whether modification of the factor (removing, reducing or increasing exposure) alters the incidence of disease
- In trial for new treatment, the design is the same, the intervention group receives new therapy and the control group receives current therapy or a placebo and the treatment outcomes are compared between the two groups
What is the aim of randomised control trials?
- Aim is to determine whether modification of the factor (removing, reducing or increasing exposure) alters the incidence of disease
What are factors to consider when interpreting results?
- Standardisation
- Techniques used to adjust for the effects of differences in age or other confounding variables when comparing two or more populations
- Before standardisation it is known as crude rates
- Standardised mortality ratio
- Special kind of standardisation, simply a standardised death rate converted into a ratio for easy comparison
- Figure for a standard reference population is 100
- So an SMR (standardised mortality ratio) below 100 is fewer than expected deaths, and above 100 is more than expected
- For example, SMR of 120 means that 20% more deaths occurred than expected in the study population
- Quality of data
- Ensure data is trustworthy
- Case definition
- Decide whether an individual has the condition of interest or not
- Important because not all doctors or investigators mean the same thing when they use medical terms
- Coding and classification
- When data is being collected it is normally converted to a set of codes to assist in data storage and analyses
- Ascertainment
- Is the data complete or are any subjects missing
What is standardisation?
- Techniques used to adjust for the effects of differences in age or other confounding variables when comparing two or more populations
What are rates known as before standardisation?
Crude rates
What is standardised mortality ratio?
- Special kind of standardisation, simply a standardised death rate converted into a ratio for easy comparison
- Figure for a standard reference population is 100
What does SMR stand for?
Standardised mortality ratio
What does a SMR below 100 indicate?
Fewer then expected deaths
What does a SMR above 100 indicate?
More than expected deaths
What does a SMR of 120 mean?
20% more deaths occured than expected in the study population
What is meant by quality of data?
- Ensure data is trustworthy
What is meant by case definition?
- Decide whether an individual has the condition of interest or not
- Important because not all doctors or investigators mean the same thing when they use medical terms
What is meant by coding and classification?
- When data is being collected it is normally converted to a set of codes to assist in data storage and analyses
What is meant by ascertainment?
- Is the data complete or are any subjects missing
What is bias?
Any trend in the collection, analysis, interpretation, publication or review of data that can lead to conclusions that are systemically different from the truth
What are different kinds of bias?
- Selection bias
- Study sample is not truly representative of the whole study population about which conclusions are to be drawn
- Information bias
- Systemic errors in measuring exposure or disease
- Such as encouraging cases more than controls to think hard about past exposures to the factor of interest
- Follow up bias
- One group of subjects is followed up more assiduously than another to measure disease incidence or another relevant outcome
- Such as subjects move address or fail to reply to questionnaires sent out, then greater attempts made to trace missing subjects from one group and not another
- Systemic error
- Form of measurement bias where there is a tendency for measurements to always fall on one side of the true value
- May be because of the instrument being calibrated wrong, or because the person is using it wrong
- Can occur with interviews and questionnaires as well as medical instruments
- Publication bias
- Where positive results have greater chance of being published than negative results
What is selection bias?
- Study sample is not truly representative of the whole study population about which conclusions are to be drawn
What is information bias?
- Systemic errors in measuring exposure or disease
- Such as encouraging cases more than controls to think hard about past exposures to the factor of interest
What is follow up bias?
- One group of subjects is followed up more assiduously than another to measure disease incidence or another relevant outcome
- Such as subjects move address or fail to reply to questionnaires sent out, then greater attempts made to trace missing subjects from one group and not another
What is systemic error?
- Form of measurement bias where there is a tendency for measurements to always fall on one side of the true value
- May be because of the instrument being calibrated wrong, or because the person is using it wrong
- Can occur with interviews and questionnaires as well as medical instruments
What can systemic bias occur due to?
- May be because of the instrument being calibrated wrong, or because the person is using it wrong
What is publication bias?
- Where positive results have greater chance of being published than negative results
What are confounding factors?
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
What are examples of common confounding factors?
Age
Sex
Social class
What are different ways of dealing with confounding factors?
- In trials, the process of randomisation
- Restrictions of eligibility criteria to only certain kinds of study subjects
- Subjects in different groups being matched for likely confounding factors
- Results stratified according to confounding factors
- Results adjusted (using multivariable analyses techniques) to take into account the suspected confounding factors
Is it easy to prove causation between exposure and disease?
Difficult to prove causation between exposure and disease
Often the best that can be achieved is to demonstrate a weight of evidence in favour of a causal relationship
What has been devised to help investigators assess the available evidence for causality?
Criteria for causality
What are examples of criteria for causality?
- Strength of association
- Measured by relative risk or odds ratio
- Consistency
- Repeated observation of an association in different populations under different circumstances
- Specificity
- Single exposure leading to a single disease
- Temporality
- The exposure comes before the disease
- Biological gradient
- Dose-response relationship, as the exposure increases so does the risk of the disease
- Biological plausibility
- The association agrees with what is known about the biology of the disease
- Conference
- The association does not conflict with what is known about the biology of the disease
- Analogy
- Another exposure-disease relationship exists that can act as a model for the one under investigation
- Such as it is known that certain drugs can cross the placenta and cause birth defects, so it might be possible for viruses to do the same
- Experiment
- A suitably controlled experiment to prove the association as causal
In terms of criteria for causality, what is meant by strength of association?
- Measured by relative risk or odds ratio
In terms of criteria for causality, what is meant by consistency?
Repeated observation of an association in different populations under different circumstances
In terms of criteria for causality, what is meant by specificity?
Single exposure leading to a single disease
In terms of criteria for causality, what is meant by temporality?
The exposure comes before the disease
In terms of criteria for causality, what is meant by biological gradient?
Dose-response relationship, as the exposure increases so does the risk of the disease
In terms of criteria for causality, what is meant by biological plausibility?
The association agrees with what is known about the biology of the disease
In terms of criteria for causality, what is meant by conference?
The association does not conflict with what is known about the biology of the disease
In terms of criteria for causality, what is meant by analogy?
- Another exposure-disease relationship exists that can act as a model for the one under investigation
- Such as it is known that certain drugs can cross the placenta and cause birth defects, so it might be psosibe for viruses to do the same
In terms of criteria for causality, what is meant by experiment?
A suitably controlled experiment to prove the association as causal
Does failure to furfil all of the criteria of causation rull our the causation?
Not necessarily
What is an audit?
Systematic approach for peer review of medical care in order to identify opportunitie for improvement and provide a mechanism for realising them
What must be done before doing an audit?
Before doing an audit need to set criteria and standards to measure:
- Could define your own
- Time consuming
- Needs more research
- Could utilise others if available
- Guidelines based on systemic review of evidence
What are disadvantages of defining your own criteria and standards to measure for an audit?
- Time consuming
- Needs more research
What is an example of an audit?
- An example is checking that all patients were prescribed the correct drugs as according to SIGN guidelines
What should be done after doing an audit?
After doing the audit should do some intervention before repeating the audit (such as with the example of prescribing drugs correctly):
- Find the ones who prescribed inappropriately and tell them not to do it again
- Present audit results to the practice
- Circulate current guideline summary to GPs
Audits have limitations, what are examples of limitations from the following:
an example is checking that all patients were prescribed the correct drugs as according to SIGN guidelines
- Sample is of those prescribed the antiviral drug only
- Misses patients who should have received the drug but never
