Unit 6-7 Flashcards
A study that does not intervene or change anything in the person’s life is called….
observational study
What type of study is an observational study?
analytical study
What are 2 types of analytical studies?
observational and experimental
What are 3 types of observational studies?
- cross-sectional
- case-control
- cohort
What are 3 types of descriptive studies?
- case reports
- case series
- descriptive surveys
What are the major differences between descriptive and analytical studies?
Descriptive:
- what?
- collects info
- does not establish association between cause and effect
Analytical:
- why?
- investigate the reason for disease/death/even to control the problem
- compares between groups
- association between E and O
- good for testing hypotheses
When would an observational study be better than experimental study?
- intervention is unethical
- intervention is expensive
- exposure is complex/hard to control
- not practical to administer exposure
How are cross sectional study subjects selected?
chosen without regard to exposure or outcome status
How are case control study subjects selected?
chosen based on outcome status
How are cohort study subjects selected?
chosen based on exposure status
What are 5 main steps in cross-sectional studies?
- randomly sample from source population
- take measurements of individuals all at one point of time
- classify E+/E-
- classify O+/O-
- compare prevalence or odds of disease in E+ or E- groups
What are some advantages of cross-sectional studies?
- can determine prevalence of E and O
- fast and inexpensive
- less bias than case control
- study permanent factors
- assess association between multiple E and multiple O
- random sampling, estimates all measures of association and effect but no true rates
What are disadvantages of cross- sectional studies?
- not good for rare E or rare O (cuz random sampling)
- prone to major forms of bias if not considered (selection, information, confounding)
- measures prevalence, but not incidence (because it takes a snapshot of one moment in time)
- temporality (prevalence, not incidence, did E actually come before O?)
What are 3 major steps for case-control studies?
- purposively sample individuals from population of interest O+ and O-
- classify each individual on basis of E+ or E-
- compare proportion of O+ subjects that are E+ vs E-
What are some advantages of case-control studies?
- rare disease (outcome), not rare exposure
- to investigate source of an outbreak
- good for identifying multiple risk factors (E) for one disease (unknown cause)
- fast and inexpensive because retrospective (historical)
What are disadvantages of case control studies?
- cannot calculate incidence or prevalence (chose on the basis of disease/not diseased
- examines only one outcome
- MOST prone to bias (looking back in time to obtain data)
- temporal relationship are issue in prevalent cases (new and old)
- control selection may be difficult to select
What is a primary study base?
population which cases arise that can be easily defined
good sense of where population of all cases are coming from
(i.e. a daycare, a farm)
(for case control studies - selecting case population)
What is a secondary study base?
population of potential study subjects that is one or more steps removed from primary study population
- wide range of backgrounds/difficult to define
(for case control studies - selecting case population)
How are cohort study subjects selected?
on the basis of exposure status
What do cohort studies measure?
incidence of disease (of new cases)
What are advantages of cohort studies?
- good for RARE exposures
- several outcomes
- temporal sequence established (prospective)
- attain incidence data
- can measure all association and effect
What are disadvantages of cohort studies?
- expensive
- time consuming
- bad for rare outcomes
- susceptible to loss to follow up
What type of study cannot calculate relative risk?
- case-control studies
What type of study can calculate all measures of association and effect?
cohort studies
- RR, OR, IRR
- RD, APe, PAR, PAF
What are 2 types of experimental studies?
Lab experiments (clinical trials) Field experiments (field trials)
these are intervention based studies
What are advantages of lab experiments/randomized clinical trials?
- highly controlled environment
- confounding factors can be controlled
- frequency and dose is set
What are disadvantages of lab experiments/randomized clinical trials?
- does not take into account of other factors /exposures in real-world scenarios
- further study required (field study)
What is a “challenge trial”
- randomized clinical trial (lab experiments)
- study of subjects exposed to given exposure (i.e. a virus)
What are advantages of field experiments/randomized field trials?
- real world setting
- assess impact of various treatments in setting that can be applied to future individuals
What are disadvantages of field experiments/randomized field trials?
- logistically more difficult to carry out than clinical
- involves healthy rather than diseased
- may not develop disease o interest in short time frame
- requires greater number of individuals to follow up for long time
What is the main/major difference between clinical and field trials?
level of control
clinical trials have total control over challenge/exposure and environment
field trials aim to see if if agent/procedure reduces risk of naturally developing disease (therefore, little control)
“Where the value of a treatment, old and new, is doubtful, there may be a higher moral obligation to test it critically than to continue to prescribe it year-in-year-out with the support merely of custom or wishful thinking”
“The question at issue, then, is whether it is proper to withhold from any patient a treatment that might, perhaps, give him benefit. The value of the treatment is, clearly, not proven; if it were, there would be no need for a trial. But, on the other hand, there must be some basis for it – whether it be from evidence obtained in test tubes, animals, or even in a few patients. There must be some basis to justify a trial at all.”
These are definitions of …
ethics
A comparison group with no intervention in randomized trials is called…
Negative control
A comparison group with an alternative intervention in randomized trials is called…
Positive control
What are 3 ways to allocate individuals to treatment groups?
- complete randomized design
- randomized block design (like stratified - grouped first by factors of interest i.e. age, ethnicity)
- cross-over design (each subject spends some time in treatment, and some time in control)
If a study subject is aware that they are receiving treatment for specific outcome and report improvements if they don’t exist, this bias is called..
Wish bias
- tendency of patients or investigators to fit data of how they believe it should be
When patients with certain characteristics are more likely to be admitted to hospital where their sample may be taken, this bias is called…
Differential admission bias
- the sample is unrepresentative of the target population
The ability/inability of study subjects to correctly remember information that occurred in the past is what type of bias?
Recall bias
Poor sensitivity or specificity of a test can lead to what type of bias?
Misclassification bias
- incorrectly classifying an individual
Blinding is useful to eliminate what type of bias?
follow up bias
What are 3 types of blinding?
- single blinding (subject OR researcher blinded)
- double blinding (subject AND researcher)
- triple blinding (subject, researcher, data analysts blinded)
What are REFLECT and CONSORT?
guidelines for randomized trials to improve level of reporting?
What does REFLECT stand for?
reporting guidelines for randomized controlled trials for livestock and food safety
(animal subjects)
What does consort stand for?
consolidated standards of reporting trials
human subjects
