PHRM3031 - Cross sectional studies

Question 1

prevalence
defintion
type of study is it is measured by?

Answer 1

the fraction of a defined population that have a particular condition
at a specific point in time (point prevalence) or at any time during a specified period (period prevalence)
eg.what proportion of a group of people has a condition at a given point in time?
-measured using cross-sectional studies
-magnitude of burden of disease

Question 2

incidence
defintion
type of study is it is measured by?

Answer 2

the rate of occurrence of new cases of a disease, adverse reaction or other event in a defined population

• the fraction of a defined population, initially free of a condition, which develops the condition over a certain period of time
• at what rate do new cases arise in a defined population over a given period of time?-measured using cohort studies
• magnitude of disease risk

Question 3

cross-sectional studies

Answer 3

• a study population is ascertained at one point in time –> all individuals are interviewed only once
• asked about their current disease status and their current or past exposures (treatment)
• investigators can try to identify a relationship (or association) between an exposure (treatment) and an outcome of interest
• sometimes called a prevalence study

Question 4

cross-sectional study advantages

Answer 4

• quick, easy and cheap to do (vs cohort studies)
• often use questionnaire based surveys
• no problems with loss to follow-up
• assess multiple exposures and outcomes at one time

Question 5

cross-sectional study

disadvantages

Answer 5

• bias (subjects and measurement)
• cannot infer a temporal association between exposure(s) and outcome(s)
• you can ONLY identify associations (not causes)
• many cases could be missed (esp. if rapidly fatal)

Question 6

calculating prevalence
formula
what is defined by the numerator and denominator

Answer 6

prevalence = number of cases observed at time t/total number of individuals at time t
ranges of 0 to 1 (a proportion), often shown as a %
numerator: number of patients with the outcome of interest (cases)
denominator: a representative sample of the total population of interest

Question 7

measures
point or period or prevalence
defintion

Answer 7

number of cases of disease in a population at specific point in time (point) or within a specified time period (period)

Question 8

measures
cumulative prevalence
definition

Answer 8

total number of cases in a population who have ever had the disease

Question 9

measures
incidence
definition

Answer 9

rate at which new cases of disease occur in a population

Question 10

measures
mortality rate
definition

Answer 10

proportion of a population that dies in a specified period

Question 11

measures
case fatality rate
definition

Answer 11

proportion of patients that die of a disease

Question 12

relationship between incidence and prevalence

Answer 12

prevalence is a function of both the incidence rate and mean duration of the disease in the population
prevalence (P) = incidence (I) x average duration of disease (D)
P=IxD or D=P/I
-increase prevalence if increase disease duration
-decrease prevalence if increase mortality rate