Disease Occurance And Study Designs Flashcards
What is the target population of a study?
Population to which we want to generalize our results
What is the source population of a study?
Population from which subjects were drawn
What is the study population?
Group actually studies
What type of measure of disease occurrence, is the number of animals that have the disease (or other condition of interest) ?
Count
What type of measure of disease occurrence is the count of animals with the disease as a fraction of the total?
Proportion (Prevalence)
What type of measure of disease occurrence is the number of diseased animals compared to healthy individuals ?
Ratio
What type of measure of disease occurrence is the frequency a disease occurs in a population over the time?
Rates (eg incidence)
What is point prevalence? What type of study usually determines this?
Proportion of animals disease at any point in time
Cross-sectional study
What is period prevalence ?
Proportion of the study population that is diseased during a specific period of time
=(#cases/period of time) / (total population/period of time)
What is incidence? What kind of studies do we use this in
The number of new cases of disease that occurs in the population over time
Prospective studies -> clinical trials/prospective cohort
What is a cumulative incidence?
Proportion of disease-free individuals that become diseased in a specified period of time
= (#new cases / time) / (total population/time)
What is a specific type of cumulative incidence used in outbreak and is usually applied to a narrowly defined population?
Attack rate
= (#new cases/time) / (#exposed/time)
What type of rate can be used when animals enter and leave a study population? How is it calculated?
Incidence rate
= (#new cases/time) / (sum of length of time that each animal is at risk)
T/F: prevalence is dependent on incidence and duration of disease
True
-> the longer old cases survive, the higher the prevalence
What is the best measure to access overall burden of disease?
Prevalence
What is the best measure to access increase or decrease in frequency of disease?
Incidence
What is mortality rate??
=(#deaths/time) / (total population/time)
What is case fatality rate?
= (#cases dead) / (total diseased)
What is cause-specific mortality rate?
= (#deaths from dz/time) / (total population/time)
What type of study does not compare groups and only has a single case?
Case report
What type of study does not compare groups, but has a few cases in the study?
Case series
What type of study does not compare groups, but has many individuals in the study?
Cross-sectional descriptive
What type of study compares groups and exposes the animals to a exposure/treatment?
Clinical trial
What type of study observes groups that are selected based on population?
Ecological study
What type of study compares group by selecting individuals to represent a population?
Cross-sectional analytical
What type of study observes individuals that are chosen to represent outcomes ?
Case control
What type of study observes individuals that are chosen to represent an exposure?
Cohort (prospective or retrospective)
T/F: cross-sectional descriptive studies can be used to estimate the amount and distribution of disease, usually with prevalence
True
What are the advantages of a descriptive cross-sectional study?
Can generalize to a population
Fast and cheap
Good descriptive baseline data
If an exposure is associated with an outcome, it is called a ________________
Determinant/risk factor
Allocation of subjects to a treatment group only occurs in experimental studies. How should allocation be done?
Randomized -> study effect of treatment with no other factors
T/F:Radom sampling is representative of a population and each subject has an equal chance of selection?
True
Non-randomized sampling may not be representative of a population. What are two ways these subjects may be sampled?
Purposive eg. Every 4th dog spayed is sampled
Convenience eg. Animals seen at vet clinics
What are advantages of experimental studies?
May establish causality
Well controlled -> free of bias and confounding
Statistically very powerful
Exposure and outcome are clearly measured (no recall bias)
What are disadvantages associated with ecological studies?
Ecological fallacy-> relationship at population level may not hold true at individual level
Cannot detect complicated relationships
A cross-sectional analytical studies selects individuals based on? What is measured?
Selected to represented population, regardless of outcome or exposure
Both exposure and outcome is measured
A case control study selects individuals based on? What is measured?
Outcome (group with dz and control)
Measure exposure between two groups
T/F: controls in a case-control study must come from the same population as the diseased individuals
True
In cohort studies, individuals are selected based on? What is measured?
Exposure status
Measure outcome
- prospective -> incidence of dz
- retrospective -> prevalence
What type of study is better and establishing causality, retrospective cohort or prospective cohort studies?
Prospective
