THEME 2b Epideiology part 2 Flashcards
What does valid mean?
actually measures what test is meant to e.g. weigh a bag of floor that is 1kg, and the scales say 1kg
What makes results reliable?
consistency and repeatable results, when done by the same examiners (thus not necessarily valid)
1) what is the prevalence of a disease?
2) what is it sometimes referred to as? why
1) the number of cases over the total population, in a specific instance.
2) - Sometimes called ‘point prevalence’ = at a given point in time.
- The ‘point in time’ may be a fixed calendar day or a fixed point in a series of events that varies from person to person e.g. the second post-operative day after G.A. for lower 8’s extraction etc).
What is the incidence of disease mean?
2) what is the formula for calculating cumulative incidence?
3) what is the formula for calculating incident rate?
Quantifies the number of new cases of a disease that develop in a population at risk during a defined time period.
2) number of new cases of a disease during a given time period/ total population at risk
3)number of new cases of a disease during a given time period/ total person -time of observation
(GOOD explanation on wiki, but basically work out number of years patients are healthy for including the ones that end up sick and the ones that are always well to find
patient-time (the denominator)
What is an index?
‘A numerical value describing the relative status of a population on a graduated scale with definite upper and lower limits designed to permit and facilitate comparison with other populations classified by the same criteria and methods’.
List the 5 uses of indices:
To describe the prevalence of a disease/condition in a population and they can be used to describe the severity of diseases/conditions.
To study and compare the health status of individuals and populations
To provide data for epidemiological studies
For planning oral health policy
To evaluate the success of preventive interventions
What are the desirable properties of indices
1) Equally sensitive across the scale, to clinically-relevant changes in disease severity and disease progression.
2) Simple to apply, objective, clear and unambiguous.
3) Should be valid (it should faithfully record the disease/condition it is presumed to identify).
4) Should be reliable (it should be consistent and repeatable at different times, by the same examiner or group of examiners).
5) The measurements gained should be amenable to statistical analysis.
6) Should be acceptable to the participant (it should not be painful nor cause harm).
what 2 ways can chance be defined?
a possibility/probability of something happening
an opportunity
Measurements we make in research are nearly always subject to ____a_____
- So are the research findings simply due to ___b____ rather than an actual ‘true’ difference / similarity?
a) random variation
b) chance
What is bias?
2) bias is what type of error?
Inclination or prejudice in favour of a particular person, thing or viewpoint. To influence unfairly
2) systemic error
What is sample bias?
Sampling bias is systematic error due to a non-random sample of a population, causing some members of the population to be less likely to be included than other
If the groups aren’t similiar at baseline what will this cause the results to be…
bias
if effective masking isn’t used in clinical trials e.g. random controlled trail, this will mean the results are ,…..
bias
Why might a large number of patients be lost in follow-up?
they died, the experiment involved unacceptable tests to the patients so they didn’t come back
What is confounding?
2) What is the cause?
A confounder is prognostically linked to the outcome of interest and is unevenly distributed between the study groups.
2) an error in interpretation of results e.g. increased ice cream sales doesn’t cause more shark attacks
