Epidemiology 2 Flashcards
What is descriptive epidemiological investigation?
Describe the problem often at an aggregated level and can be sued to inform later analytic research
What is descriptive epidemiological investigation?
Deploy and test hypotheses often at a person-level through which association can be measured and causation inferred
What are the type of descriptive epidemiological investigation?
- Case report
- Case series
- Cross sectional (sometimes analytical)
- Longitudinal
- Ecological (sometimes analytical)
What is a statistic?
A fixed value, derived from a sample that estimates the value in the population
What is a parameter?
-A fixed, often unknown value, which describes an entire population
What is a point estimate?
statistic that seeks to estimate parameter
What is a confidence interval?
range of values within which we are 95% that the true value lies
What is a case report and case series?
- Used to communicate new disease, new presentation or new findings
- Unusual findings structured as a bulletin or as learning opportunity in CME or UK CPD
- In new disease more than one case reported becomes a case series
What is a cross sectional study?
typically describes the prevalence of a condition across a population as a single point in time
What is an example of a cross-sectional study?
A snapshot as a single point intimate e.g. survey (cheap and easy to empty) - assume point estimate relates to a point in time e.g. a particular month or year and can be questionnaire or blood sample
What is benchmarking?
take point estimate of our population and compare to similar area or national average or some other metric
What is bad about cross-sectional study?
- Single snapshot
- The prevalence measured but not incidence rate or risk
- Lacks follow-up so risk or temporal relationships cannot be easily determined - but cheap and easy, can’t see causal relationship
What is a longitudinal study?
descriptive longitudinal studies describe the prevalence or incidence of an exposure or outcome over time
What is an example of a longitudinal study?
- May be made up of more than one cross-sectional analysis: that is aggregated data (as long as ask same qs in same population)
- Or may look to follow the same participants over time: that is person-level data
What is an ecological study?
- Compare groups (rather than individuals)
- Can be descriptive or analytic in nature
What type of epidemiology is used more in public health setting?
Descriptive
What type of epidemiology is used more in research setting?
Analytic
What type of epidemiology involves hypothesis testing and the use of statistical test?
Analytic
Which type of epidemiology provides estimates of morbidity such as prevalence or incidence rate?
Descriptive
Which type of epidemiology identifies the impact of interventions or specific exposures?
Analytic
What happens if confidence intervals overlap?
Can infer that there is no statical difference between the two variables, despite apparent gap in point estimates
What is the range of confidence interval inversely proportional to?
Sample size
When do you do ecological studies?
ndividual level data not alway available and hard to collec
What do you focus on in ecological studies?
- Focus on comparison of groups, unit of observation is group, analyse on aggregate data
- School, or work site or country can be group/unit of analysis
What can units be in ecological studies?
geographically defined or occupation or time interval
What data do you used in ecological studies?
- Aggregate data on exposure and outcome on group level
2. Then take a number of groups and use aggregate data in analysis
What is ecological fallacy/aggregation bias?
Assuming that association between groups holds for individuals
When do you use ecological studies?
- first step in exploring research q - used in hypothesis generation
- Use secondary data sources that are already available as inexpensive - sometimes level of inference interested in is at population level anyway
- With limited time and resources helpful ecological
Why is relying on secondary data bad?
may not be comparable for country or time period - and don’t know if exposure preceded outcome
What does descriptive epidemiology achieve?
providing measures of frequency
What does analytic epidemiology achieve?
testing hypotheses and associations
What is the difference between aggregated and person-level data?
- Aggregated data: for example, 5% of the population died
2. Person-level data: for example, participants 1, 7 and 15 died
What is primary data?
those that are collected by the researcher first-hand
What are the positives of primary data?
will have been collected for a pre-specified purpose: to test the hypotheses or answer the research question(s) set by the researcher
What are the negative of primary data?
financial and time cost
What is secondary data?
term applied to data that have been collected for another purpose – and then potentially ‘recycled’ for a different purpose
What are the negative aspects of secondary data?
- analyses may have to make a series of assumptions because the data analysed weren’t intended for the new purpose
- may in turn introduce critical limitations on how the findings of such a study are interpreted
What are the benefits of secondary data analysis?
faster and cheaper
What is routinely collected data?
day-to-day demography and epidemiology in the field
What is an example of routinely collected data?
Census (but almost always out of date)
How can we improve understanding of a local area?
- Looking at the number of patients registered in a general practice or on the electoral register
- The first language of reception-class school children can often give us a good understanding of changing ethnic diversity in a local area.
What is the hospital episode statistics?
can examine emergency department attendances, hospital admissions and outpatient attendances from the last ten years
How can you examine describing data?
Billing data of pharmacies
What is non-routinely collected data?
corollary to primary data
What is an example of non-routinely collected data?
surveys and other bespoke datasets
Why is non-routinely collected data limited use?
professional practice (outside research) non-routinely collected data are usually prohibitively expensive and time-consuming to operate, so their use is limited
What is data linkage?
joining two or more datasets together and in doing so, finding out more than was possible by analysis of either original dataset alone
Why are primary and secondary care systems not connected?
- Technical issues: despite multiple attempts to join up health records, we’ve repeatedly failed as a health service to deliver the technological platform or solution necessary.
- Privacy concerns: there are very reasonable ethical questions and accompanying legal constraints on how we hold, exchange and analyse health information
However, most patients are surprised that health records are not routinely shared and express frustration at having to provide the same information repeatedly to multiple organisations that they regard as being the same NHS.
What are the two types of analytical studies?
- Observational
2. Experimental
What is an observational study?
don’t manipulate or interfere exposure
What is a case control study?
Comparing individuals with condition or disease (cases) with a group of individuals with the same characteristics but without conditions (controls) - info on past exposure of risk factor obtained for both controls and and frequency and intensity of exposure compared
How do you identify cases in case control studies? What are examples of sources of cases?
- clear eligibility criteria must be defined - referred to as case definition
- source of cases: hospitals, community and clinic - all cases should be representative of everyone with the disease under investigation e.g. not just the ones who needed surgery
How do you select controls?
controls should come from the same study population as the cases and should be representative of the population at risk
How do you asses exposure in cases and controls?
exposures within controls should be measurable with similar accuracy to exposure in the cases
When might there be recall bias in assessing exposure?
Self reported recall of usual behaviour may not be comparable in cases and controls e.g. cancer may be more motivated as to why disease, so think of past differently and report differently than if no cancer
How do you determine how many cases and controls?
limited by rarity of disease, so statistical confidence increased by more than 1 control per case
What are the advantages of case control studies?
- Good for studying rare disease, as identify all disease
- Inexpensive to conduct
- Quick to obtain data as can asses outcome and exposure at same time
What are the disadvantages of case control studies?
- Bias associated with exposure assessment (presence of disease may affect how someone reports past exposure)
- Difficulty in selecting good control group
- Limited to assessing just one outcome
- Cannot provide information about temporal relationship between exposure and disease