1. B.) Measuring Health Outcomes Flashcards
What is the significance of defining a case?
• Enable diseases to be counted and compared
across sites and countries
• Require standardised criteria
• Minimises false positives and negatives
What are the criteria within defining diseases?
- Clinical criteria
- Epidemiological risk factors
These criteria can lead to you being confirmed as either a problem or confirmed case.
What factors should be taken into account when deciding a case definition?
- The severity of the disease.
- If there are diagnostic tests available (how stringent should your classification be if there are none and you are unsure).
- How infectious/easily spread is the disease.
Why measure the frequency of disease?
Frequency enable researchers to count and
describe the number of cases within a population.
What is prevalence?
“The total number of individuals who have the
condition (disease, exposure, attribute) at a
particular time (or during a particular period) divided
by the population at risk of having the condition at
that time or midway through the period”
How do point and period prevalence differ?
Point prevalence – specified point in time
Period prevalence – specified time period e.g. One-year prevalence
What is the incidence?
“The number of instances of illness commencing, or
of persons falling ill, during a given period in a
specified population. More generally, the number of
new health-related events in a defined population
within a specified period of time. It may be measured
as a frequency count, a rate, or a proportion”
- Incidence can be measured as a risk or a rate.
What is a risk?
“The probability of an adverse or beneficial event in
a defined population over a specified time interval. In
epidemiology and clinical research it is commonly
measured through the cumulative incidence or the
incidence proportion”
Here is an example of risk.
In a study of infants followed up over 6 months 68
out of 360 had infantile colic
• 68/360 = 0.188
• Multiply by 100 to express as a percentage (%):
• 0.188 x 100 = 18.8%
In this sample 18.8% of infants had infantile colic.
The risk can be expressed as a proportion (0.188) or as a percentage (18.8%).
What is the rate?
“A measure of the frequency of occurrence of a
phenomenon. In epidemiology, demography, and
vital statistics, a rate is an expression of the
frequency with which an event occurs in a defined
population, usually in a specified period of time.”
Here is an example of rate.
Incidence rate = number of new cases of disease during a given time period/total person time in observation.
(e.9 4 cases/108 total person time (sum of months or years of each individual) = 0.44 cases of influenza per 1 person year or 4.4 cases per 10 person years or 44 cases per 100 person years.
What is an odd?
“The ratio of the probability of occurrence of an
event to that of nonoccurrence”
What is a 2X2 table.
Far left collum = Exposure
Collums = Outcome
Calculating Odds Ratio.
The Odds Ratio is defined as the odds of disease, so the
outcome in one group divided by the odds in the
other.
How to calculate the odds and odds ratio?
Dependent on what variable you are discussing. For example if you are talking about the odds of dying, always put the dying count ON TOP, or if you are discussing intervention put that ON TOP. E.G =
Intervention Women = 5/10 = 0.5 odds of dying.
The odds ratio would be = odds after intervention/odds before intervention.
