Term
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Definition
| Incidence is the frequency of an event occuring over a set period of time |
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Term
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Definition
The number of cases of a disease at any ONE TIME.
P for prevalence, P for photo. It's a snapshot look at things |
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Term
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Definition
| Proportion of disease free animals developing disease during a specific time period. (Assumes closed population) |
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Term
| Animals 'at risk' are ones that |
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Definition
- Can get the disease
- Can be diagnosed as having the disease |
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Term
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Definition
Number of new cases over a period of time
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Accumulated sum of all individual's time at risk
OR, for large populations:
Cases
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(start – ½ diseased – ½ withdrawn – ½ added) x time |
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Term
| What is the difference between incidence rate and risk? |
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Definition
Both use the number of new cases occurring over time amongst an initially disease free population.
The incidence rate has time as a denominator, while risk has the number of 'at risk' animals at the beginning of the study as a denominator.
I.rate measures the rapidity of which new cases develop, while I.risk measures the risk of disease developing over time. |
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Term
| Is prevalence or incidence a better measure for a rare disease? |
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Definition
| Incidence is better because prevalence may not capture the disease in its 'snapshot' if the disease is very rare |
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Term
| Describe the difference in incidence and prevalence of a long term (chronic) disease |
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Definition
Population incidence will be lower, though the prevalence will be higher.
For example, the prevalence of chronic disease in a general population is growing because of both the higher incidence of chronic diseases (there are more cases each year than in the past) and the longer survival of patients with chronic disease resulting from modern treatments. If death rates drop, then the time that patients live with chronic disease grows and even a low incidence will produce a high prevalence. |
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Term
| What is a component cause? |
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Definition
| A contributing factor to disease (e.g. smoking for lung cancer or high cholesterol for heart disease) |
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Term
| What is a sufficient cause? |
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Definition
The combination of conditions/causes without any one of which the disease would not have occurred.
E.g. Respiratory disease in calves
• Pasteurella spp., respiratory syncitial virus, stress
• Disease occurs when two or more of these occur – Sufficient
causes |
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Term
| What is a necessary cause? |
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Definition
The most important piece of the pie - must be present for
disease to occur
• Example: Foodborne disease outbreak
• Sufficient causes: Chicken salad and cream desert
• Necessary cause: Salmonella spp |
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Term
| How do you calculate the risk ratio for a disease? |
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Definition
| Ratio of incidence risk in exposed group to incidence risk in unexposed group |
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Term
| How do you interpret a risk ratio? |
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Definition
<1 = protective
1 = no association
> 1 = increased risk |
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Term
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Definition
Let p = the probability of an event
1-p = the probability that the event does not occur
Odds of the event = p/1-p
Odds of disease in exposed group divided by odds of disease in unexposed group |
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