Frequency of Clinical Events

Question 1

Disease control levels

Answer 1

Primary care
- actions to prevent disease
Secondary care
- actions to detect disease early, with intention to reduce impact
Tertiary care
- actions to extend/improve life after diagnosis

Question 2

Return on dollars invested is highest with ______ and lowest with _______

Answer 2

Primary care; tertiary care

Question 3

Generalized disease pathway

Answer 3

Induction
- exposure, interaction, undetectable
Incubation/latent period
- local onset, detectability
Signs
- systemic affect, clinical manifestation, tissue destruction

Question 4

True experiments

Answer 4

Subjects are randomized to treatment, and receive specific treatments
- randomization and control

Question 5

Quasi-experiments

Answer 5

Like a true experiment except no randomization

- control without randomization

Question 6

Observational studies

Answer 6

Neither randomization nor control

- subjects self select their treatment

Question 7

Ecologic observational studies

Answer 7

Ecologic, heterodemic, community level studies

- entire farms, communities, shelters, families are the subject

Question 8

Measures of disease frequency

Answer 8

Rate versus risk

Question 9

Measures of association

Answer 9

Assessing risk factor (disease)

• age, breed, sex, production cycle
• relative risk, odds ratio, incidence density ratio

Question 10

Measures of disease impact

Answer 10

Attributable risk, attributable difference, population attributable risk
- assess impact of exposure in the population

Question 11

Relative frequency

Answer 11

Use proportions, ratios, rates

Question 12

Incidence

Answer 12

Expression of the force of disease

• applied to new cases in a period
• indicates movement from well to diseased
• a person can only be an incident case once!

Question 13

2 ways to express incidence

Answer 13

• incidence rate (incidence density)

- cumulative incidence (risk, incidence proportion, attack rate)

Question 14

Rate

Answer 14

An expression to describe a change in one quantity with respect to another quantity with the denominator featuring a time component
- denominator is in person/animal-time

Question 15

Incidence rate formula

Answer 15

of new cases over a time period / sum (over all individuals) of the length of time at risk of developing disease

Question 16

How long do you count the time for incidence rate?

Answer 16

Count time until:

• animal gets disease
• death from another case
• removed from herd
• study terminates
• animal undergoes intervention to render it non-susceptible

Question 17

Simple cumulative incidence

Answer 17

Proportion of non-diseased individuals at the beginning of a period of study that become diseased during the period

• individuals must start out non-diseased, in order to be at risk for new disease
• at risk means they can get the condition

Question 18

Cumulative incidence formula

Answer 18

of new cases over a time period / # of healthy animals at beginning of time period

Question 19

Attack rate

Answer 19

Cumulative incidence rate for an outbreak

• numerator: # of new cases
• denominator: # of individuals exposed at the start of an outbreak or for a limited time

Question 20

When is attack rate appropriate to use?

Answer 20

When exposure occurs in a very short and defined period of time

• affects very specific and defined populations
• ex: food poisioning, neonatal period, acute exposure to radiation

Question 21

Cumulative incidence does not account for _______

Answer 21

Animals that fall out of observation

- adjust with actuary table/measurement to account for periods with no data for a specific animal

Question 22

Incidence rate summary

Answer 22

• precise expression of disease force
• applicable to a group
• 100 animal-years can be accumulated several ways
• hard to interpret, less often used than CI

Question 23

Cumulative risk summary

Answer 23

• very easy to interpret
• applicable to group or individual
• problematic when animals are lost in the time window
• similar to IR, reflects an overall average, disease force in the time window

Question 24

Measures of frequency

Answer 24

• levels of control (primary, secondary, tertiary)
• incidence (defined!)
• rate (incidence density)
• risk (cumulative incidence_