7: Study Design II Flashcards
Describe a cross-sectional study
- Occurs at a single point in time.
- Divide the study population into 2 groups (case and controls), and assess the 2 groups by exposed/ not exposed
What can you estimate with cross-sectional studies?
Prevalence/ risk of outcome & exposure
What are advantages and disadvantages of cross-sectional studies?
+ quick (for assessment of disease and method for establishing who is ill) and cheap
+ can be done serially for changes over time
+ may be planned before cohort study
+ good first step for hypotheses
- no temporal relationship
- casual relationships are difficult to determine
- potential for selection and recall bias
- not good for exposures/outcome (eg is X a rare outcome?)
Is screening a form of cross-sectional survey?
+ done at one point in time
+ can be repeated at intervals
+ determines who is ill
Yes
Why does lung cancer screening not currently exist?
Lung cancer as a whole doesn’t have a defined age range
It would be expensive to screen everyone
It may not be ethical to screen populations most at risk (eg SES)
Describe multi-stage sampling and why it is used
- deinfed population of cases and controls clustered
- clusters are randomly selected for sampling
- randomization is used for avoiding bias
- it is used as it is quicker and cheaper than sampling a whole population
What is an example of a successful serial cross-sectional study?
- 2000-2013 sexual behaviours, HIV testing, and the proportion of men at risk of transmitting HIV in London
- 2 cross-sectional samples in 2000 and 2013 showed a successful launch of HIV/sexual health campaign
- reduction in unprotected intercourse
Are surveys a good method for cancer epidemiology?
- cancer is relatively rare, so no
- surveys are better for assessing risk factors (smoking, diet)
- good for screening and heath care usage for cancer patients
How can you analyze survey data?
- estimate hazard risk ratios (similar to cohort)
- estimate odds & odds ratio ( similar to case-control)
- must look for confounding factors eg age, smoking, etc
Describe census data in the UK
- everyone s surveyed in England and wales
- occurs every 10 years
- questions include: no of people in household and relations, type of house & ownership, marital status, ethnicity, religion, education, employment, long term health conditions
What are some examples of studies using census data?
- 1991-2011 patterns of mortality by occupation
- associations between commute mode and cardiovascular disease, cancer, and mortality across 25 years
- fall in smoking prevalnce across UK from 2011
- adult BMI status by sex 2018
What are some examples of courses of data for routinely collected data studies?
- cancer registry
- death certificate
- hospitals admission data
- general practise records
T or F
- GDPR regulations state anyone’s clinical care data can be used in studies
- Death certificate data can be used in data collection studies
- F: anyone can opt-out
- T
Why might some data not be eligible for use in routinely collected data studies?
- data may be lost to follow up
- the test may have been wrong or disputed
- they may have died before diagnosis (zero survival)
Describe the trend in the routinely collected data study on mesothelioma mortality in Britain
- in 2020 there was high levels of mesothelioma deaths despite intervention
- late affect due to asbestos regulations in place, a drop after 2020 is now showing in statistics
- late onset of mesothelioma after exposure to asbestos
Describe the usage of GP data in the UK in studies
- all data is anonymized
- datasets include CPRD, THIN, Qresearch, System 1
- combining datasets improves coverage
- ate its can opt-out due to GDPR regulations
What is an ecological study?
- an observational study (does not introduce exposure)
- unit of analysis is populations (not individuals)
- they are most commonly cohort or cross-sectional surveys
Give an example of a successful ecological study
Olive oil, diet, colorectal cancer ecological study from 2000.
Storing positive correlation between meat consumption across countries and CRC rates per 100,000
What are the + and - of ecological studies?
+ quick and cheap, data acquired from routine sources
+ good for early idea testing
+ some exposures are measured well at community level eg pollution, diet, stress
- ecological fallacy
- results cannot be directly applied to individuals
- adjust for confounding
How are ecological studies analyzed/measured?
- degree of association: correlation coefficient
- +1 positive, 0 no correlation, -1 negative
Describe the idea of ecological fallacy with an example
Relationships from ecological studies disappear when analysed at individual levels.
Eg: higher levels of fat consumption in the population are correlated with hate rates of BC. It would be incorrect to assume that a woman who eats more fat in her diet is at a higher risk of BC.
