Measures of Frequency, Association and Impact Flashcards
What are the basic measures?
Count- no comparison
Proportion
Odds- 4:1
Rate- needs time
What are the two most important measures of frequency?
Incidence
Prevalence
What is the difference between incidence and prevalence?
Incidence is frequency of new cases during a period where as prevalence is the proportion of all animals in a specific time
What is the commonly used measures of incidence?
Cumulative incidence/ incidence risk
What does incidence show about a disease?
The amount of risk of contracting the disease
What is needed for incidence?
A clear case definition, surveillance programme which identifies cases, to show its a new case
What is cumulative incidence?
The proportion of disease-free individuals developing a given disease over a specified time
How is cumulative incidence calculated?
Number of new cases during period/
population at risk during same period
How is prevalence calculated?
Number of cases at time/
total number of animals at risk at time
What is the difference between point and period prevalence?
Point is a single point in time, period is number of cases over defined period of time
What does prevalence show about a disease?
How widespread a disease is
What is needed for prevalence?
Cross sectional studies, no idea about temporality
How does duration of a disease effect incidence and prevalence?
High incidence but short duration causes low prevalence
Low incidence but long duration causes high prevalence
What are measures of association used to assess?
The magnitude of the relationship between risk factor and outcome
What are the 2 types of relative measures?
Relative risk, odds ratio
What are the 2 types of absolute measures?
Risk difference, attributable fraction,
What kind os studies are used for relative risk?
Cohort and cross sectional
How is the relative risk ratio calculated?
risk of disease in exposed/
risk of disease in unexposed
What does relative risk measure?
The strength of association
What is odds?
The probability of an event occurring divided by the probability of the event not occurring
How is odds ratio calculated?
Odds of disease in exposed/
Odds of disease in non-exposed
How can odds be interchanged?
Odds of exposure can be used
What king of studies is odds ratio used?
Case-control studies
What does it mean if the RR/OR are below 1, equal to 1, over 1?
<1- decreased risk
=1- no change
>1- increased risk
What can make a RR/OR insignificant?
If the confidence interval crosses 1
What is the problem of measures of association?
Don’t show the frequency of disease or the amount of disease that results
What is the measure of impact of exposed?
Attributable risk
How is attributable risk calculated?
Risk among the exposed- risk among the unexposed
