Can anyone explain please how does incidence data work? For example as a hypothetical example, let's say that for a particular disease, an incidence data for 3 years (between 2009 and 2012) is 6/100,000, then is it possible to calculate (or estimate) the incidence data for 1 year (lets say 2012) by dividing by 3?
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Step I Question about incidence?
Started by I_love_UMKC
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HY Behavioral Science 2e pg. 108
"...number of individuals who newly develop an illness in a specific time period divided by the total number of individuals at risk for the illness during that time period;"
"...number of individuals who newly develop an illness in a specific time period divided by the total number of individuals at risk for the illness during that time period;"
Right, I understand that, but that still doesn't answer my question...
In short, no. Without being provided additional data, you have no way of knowing the incidence for just the sole year of 2012. In this example, you're stating that incidence for a particular disease is 6/100,000 *during this particular time period*.
Knowing information about this time period doesn't tell you about a different time period, or about a subset of that time period. It's possible that there were four new cases during 2009, two during 2010, and zero during 2011 and 2012.
Just as an aside, don't forget that if you're including years 2009 through 2012, that's actually four years and not three.
Is that incidence or prevalence!
Incidence refers to the number of new cases that occurred during a given time period (as McGillGrad stated). Measuring incidence requires specifying an interval. There's no such thing as incidence at a specific point in time.
Prevalence is a point-in-time metric. It tells you how many cases already exist at a given point in time. Prevalence is not used with time periods, and there's no such thing as prevalence for a time interval. With that said, prevalence can change over time. But it doesn't measure something changing over time.
