Epidemiology Flashcards
What is epidemiology?
How often diseases occur in different groups and why
What is primary prevention?
Control of exposure to risk factors
What is secondary prevention?
Detection of early departures from health and treatments to slow progression of disease
What is exposure?
the variable that we are trying to associate with a change in health status
What is outcome?
Result of the exposure
Name three examples of exposures in epidemiology
Drugs, behaviours, demographic characteristics
What is epidemiological transition?
changing patterns of population distributions in relation to changing patterns of mortality, fertility, life expectancy, and leading causes of death
Which diseases are more prevalent in resource constrained societies?
Infectious diseases
How can infectious diseases be overcome?
improved access to water, sanitation, hygiene, vaccines and antibiotics
Which diseases are more prevalent in well-resourced societies?
Non-communicable diseases
What are the three groups of diseases?
Communicable
Non-communicable
Injuries
What are disability adjusted life years/DALYs?
measure of disease burden that combines years of life lost from ill-health, disability or premature death
What are the four measures of frequency?
Odds
Prevalance
Cumulative Incidence
Incidence Rate
What is the correct epidemiological definition of odds?
The ratio of the probability (P) of an event to the probability of its complement (1-P)
What is the epidemiological definition of prevalence?
The proportion of individuals in a population who have the attribute at a specific timepoint
What is the epidemiological definition of cumulative incidence?
The proportion of the population with a new event during a given time period.
What is the epidemiological definition of incidence rate?
The count of new cases during the follow-up period, divided by the total person-time
What is person time?
an estimate of the actual time-at-risk that all participants contributed to a study (can be in months, days, years, etc)
Which measures of frequency are time dependent?
Cumulative incidence and incidence rate
What is an advantage of incidence rate over cumulative incidence
Participants can join or leave the study at any time
What is a disadvantage of cumulative incidence?
All patients must enter study and have follow up at the same time.
What is standardisation in epidemiology?
A way to summarise disease rates or mortality in different populations, taking account of variations in age structure, sex or other potential confounders, so that comparisons between populations remain meaningful.
What is direct standardisation?
A type of adjustment which allows us to compare like-for-like between populations. Provides a comparable incidence
What do you need for direct standardisation?
Age/sex-specific incidence and a standard population
Can the crude incidence be higher/lower than the direct standardised incidence?
Yes
Does a higher incidence of disease in one area compared to another also mean that there are more people with the disease in that area?
No, depends on population size
What is indirect standardisation?
Where the number of events or the mortality rates in each age group is unknown. Provides a ratio out of 100/1
When is indirect standardisation used?
When we don’t know age/sex-specific data
What is unwarranted variation?
Higher mortality due to dangerous practise
What is explained variation?
Higher mortality that is not due to malpractice e.g. higher risk blend of procedures
What is statistical artefact
Higher mortality due to better recording of mortality rather than more deaths occurring
Why is the blend of procedures easier to find out than who is getting the procedures
Billing for procedures
What do we need for indirect standardisation for hospital mortality
Procedure bills and national mortality statistics for each procedure
What is the standardised mortality ratio/SMR?
The ratio of observed deaths to expected deaths (O:E)
What is the standardised incidence ration/SIR
The ratio of observed cases of a disease in a population to expected cases (O:E)
What is the Summary Hospital-level Mortality Indicator/SHMI?
Indicator which uses the process of indirect standardisation to produce ‘expected’ number of deaths. Identifies hospitals with higher than expected mortality.
What are the two types of literature review?
- narrative review
- systematic review
What is a narrative review?
Brings together the published literature into a single article enabling the reader to quicklly understand the issue
What is a systematic review?
Sets out a highlt structred approach to searching, including and summarising literature, often presented as the basis for meta-analysis
What are the strengths of narrative reviews?
- easier and faster to write so may be more up to date
- useful for looking at areas with limited research
- useful for when work from different disciplines is being brought together with a research question that is difficult to answer
What are the limitations of narrative reviews?
- subject to bias since authors are free to pick and choose which research is included
- some evidence may be omitted by chance
What are the strengths of systematic reviews?
- collate all available evidence that relates to a highly focused research question
- structured search enables reproducability
- inclusion criteria for evidence
- can take many months to design
What is the process of a systematic review?
- research question
- structured search
- indices
- screening/inclusion
- reporting
- writing
- submitting, revising and publishing
How long can systematic reviews take to publish?
18-24 months
What is a structured search?
A technology for querying multiple data sources in an independent and scalable manner. It occupies the middle ground between keyword search and database search.
What are indices in research?
- Lists of all the names, subjects and ideas in a piece of written work, designed to help readers quickly find where they are discussed in the text
- e.g. medline, mbase, psychinfo, etc
- must be made clear which search indices where used and the time period
What is the difference between an index and registry?
- index = based on published research
- registry = registration of research which is incomplete or unpublished
Why are registries important?
To prevent duplication, omission and bias in research
What is the PRISMA diagram?
- a flow diagram which visually summarises the screening process
- the four stages are identification, screening, eligibility and included
- shows the n at each stage
How many pieces of evidence will be found at the beginning and end of the screening process?
- start with 1000-3000
- end with 10-30
What are the limitations of systematic reviews?
- only as good as the method used, indices searched and evidence incorporated
- become outdated very quickly - need to look at the search date not the publication date
What is grey information/literature?
- literature that has not be reviewed and published through academic journals
- hasn’t been peer reviewed and won’t be found on online indices like pubmed
- can be found on Google Scholar and OpenGrey
- e.g. government reports
Can grey literature be incorporated into research?
Yes but with caution
How are narrative and systematic reviews useful?
- as a starting point
- can look into the individual literature that makes up the reviews
- can look into more recent citations of the reviews using online indices
What is the Cochrane Collaboration?
- the world’s largest organisation dedicated to the preparation and maintenance of systematic reviews
- aims to help people make well-informed health decisions
What is a meta-analysis?
a statistical process that combines the data of multiple studies to find common results and to identify overall trends
How is a meta-analysis different to a systematic review?
- systematic review = combining study data in a number of ways to reach an overall understanding of the evidence
- meta-analysis = combining the quantitative findings of several separate studies into one pooled estimate
How are the pooled estimates of a meta-analysis presented?
Forest plot
What are the components of a forest plot?
- Studies
- Intervention group
- Control group
- Relative risk (shown numerically and on forest plot)
- Weight
What do the intervention and control group together show?
The number of participants in the study
What does the vetical line at one in a forest plot indicate?
the line of no effect
What are the size of the squares in a forest plot proprtional to?
The number of participants in the study
What do the whiskers around the squares in a forest plot show?
the level of confidence
What does the position of the squares in a forest plot indicate?
- left of line of no effect = negative effect/attenuation
- right of line of no effect = positive effect
Which side of the line of no effect will the null hypothesis be on in a forest plot?
can be either side depending on what is being investigated
What does the diamond in a forest plot represent?
The pooled estimate
What do the left and right points of the diamond represent in a forest plot?
levels of confidence
What does it mean when the lateral point of a diamond crosses the line of no effect in a forest plot?
level of confidence is low, cannot reject the null hyposthesis
What is heterogeneity in meta-analysis?
The differences between the studies being pooled
What are the three types of heterogeneity we are concerned with?
- clinical (patients, selection criteria)
- methodological (study design, blinding, intervention approach
- statistical (differences in reporting)
What are the two ways of weighting in a meta-analysis?
- fixed effects
- random effects
What is a publication funnel plot?
assesses the likelihood of publication bias arising
What is a trial endpoint?
an outcome that usually describes a clinically meaningful outcome
e.g. survival in cancer trials
Should the endpoint be a priori or a posteriori?
a priori
What are the measures for clincial trial outcomes?
- Saftey (a)
- Efficacy (how well a therapy works in achieving a desired outcome)
What are the two types of efficacy endpoint?
primary and secondary
What is a primary efficacy endpoint?
the endpoint for which the study has been made
What is the secondary efficacy endpoint?
- a second, ‘softer’ measure that is studied alongside the primary endpoint
- can still be usefful even if the primary endpoint isn’t proven
What is the composite endpoint?
- multiple potential endpoints added together
- common when the outcomes measured are uncommon
What is survival analysis?
d
What is used to portray survival analysis?
Kaplan-Meier plots
