Disease Occurance And Study Designs

Question 1

What is the target population of a study?

Answer 1

Population to which we want to generalize our results

Question 2

What is the source population of a study?

Answer 2

Population from which subjects were drawn

Question 3

What is the study population?

Answer 3

Group actually studies

Question 4

What type of measure of disease occurrence, is the number of animals that have the disease (or other condition of interest) ?

Answer 4

Count

Question 5

What type of measure of disease occurrence is the count of animals with the disease as a fraction of the total?

Answer 5

Proportion (Prevalence)

Question 6

What type of measure of disease occurrence is the number of diseased animals compared to healthy individuals ?

Answer 6

Ratio

Question 7

What type of measure of disease occurrence is the frequency a disease occurs in a population over the time?

Answer 7

Rates (eg incidence)

Question 8

What is point prevalence? What type of study usually determines this?

Answer 8

Proportion of animals disease at any point in time

Cross-sectional study

Question 9

What is period prevalence ?

Answer 9

Proportion of the study population that is diseased during a specific period of time

=(#cases/period of time) / (total population/period of time)

Question 10

What is incidence? What kind of studies do we use this in

Answer 10

The number of new cases of disease that occurs in the population over time

Prospective studies -> clinical trials/prospective cohort

Question 11

What is a cumulative incidence?

Answer 11

Proportion of disease-free individuals that become diseased in a specified period of time

= (#new cases / time) / (total population/time)

Question 12

What is a specific type of cumulative incidence used in outbreak and is usually applied to a narrowly defined population?

Answer 12

Attack rate

= (#new cases/time) / (#exposed/time)

Question 13

What type of rate can be used when animals enter and leave a study population? How is it calculated?

Answer 13

Incidence rate

= (#new cases/time) / (sum of length of time that each animal is at risk)

Question 14

T/F: prevalence is dependent on incidence and duration of disease

Answer 14

True

-> the longer old cases survive, the higher the prevalence

Question 15

What is the best measure to access overall burden of disease?

Answer 15

Prevalence

Question 16

What is the best measure to access increase or decrease in frequency of disease?

Answer 16

Incidence

Question 17

What is mortality rate??

Answer 17

=(#deaths/time) / (total population/time)

Question 18

What is case fatality rate?

Answer 18

= (#cases dead) / (total diseased)

Question 19

What is cause-specific mortality rate?

Answer 19

= (#deaths from dz/time) / (total population/time)

Question 20

What type of study does not compare groups and only has a single case?

Answer 20

Case report

Question 21

What type of study does not compare groups, but has a few cases in the study?

Answer 21

Case series

Question 22

What type of study does not compare groups, but has many individuals in the study?

Answer 22

Cross-sectional descriptive

Question 23

What type of study compares groups and exposes the animals to a exposure/treatment?

Answer 23

Clinical trial

Question 24

What type of study observes groups that are selected based on population?

Answer 24

Ecological study

Question 25

What type of study compares group by selecting individuals to represent a population?

Answer 25

Cross-sectional analytical

Question 26

What type of study observes individuals that are chosen to represent outcomes ?

Answer 26

Case control

Question 27

What type of study observes individuals that are chosen to represent an exposure?

Answer 27

Cohort (prospective or retrospective)

Question 28

T/F: cross-sectional descriptive studies can be used to estimate the amount and distribution of disease, usually with prevalence

Answer 28

True

Question 29

What are the advantages of a descriptive cross-sectional study?

Answer 29

Can generalize to a population
Fast and cheap
Good descriptive baseline data

Question 30

If an exposure is associated with an outcome, it is called a ________________

Answer 30

Determinant/risk factor

Question 31

Allocation of subjects to a treatment group only occurs in experimental studies. How should allocation be done?

Answer 31

Randomized -> study effect of treatment with no other factors

Question 32

T/F:Radom sampling is representative of a population and each subject has an equal chance of selection?

Answer 32

True

Question 33

Non-randomized sampling may not be representative of a population. What are two ways these subjects may be sampled?

Answer 33

Purposive eg. Every 4th dog spayed is sampled

Convenience eg. Animals seen at vet clinics

Question 34

What are advantages of experimental studies?

Answer 34

May establish causality
Well controlled -> free of bias and confounding
Statistically very powerful
Exposure and outcome are clearly measured (no recall bias)

Question 35

What are disadvantages associated with ecological studies?

Answer 35

Ecological fallacy-> relationship at population level may not hold true at individual level

Cannot detect complicated relationships

Question 36

A cross-sectional analytical studies selects individuals based on? What is measured?

Answer 36

Selected to represented population, regardless of outcome or exposure

Both exposure and outcome is measured

Question 37

A case control study selects individuals based on? What is measured?

Answer 37

Outcome (group with dz and control)

Measure exposure between two groups

Question 38

T/F: controls in a case-control study must come from the same population as the diseased individuals

Answer 38

True

Question 39

In cohort studies, individuals are selected based on? What is measured?

Answer 39

Exposure status

Measure outcome

• prospective -> incidence of dz
• retrospective -> prevalence

Question 40

What type of study is better and establishing causality, retrospective cohort or prospective cohort studies?

Answer 40

Prospective