You have the option to display limited-duration prevalence statistics for time periods prior to the prevalence date. That is, in addition to the statistics for the total period specified, you can specify sub-periods in the analysis. For example, in addition to 25-year limited-duration prevalence, you may want to show statistics for people diagnosed <= 5 years, 5-10 years, and 10-25 years prior to prevalence date (discrete). Alternatively, you could show statistics for people diagnosed <= 5 years and <= 10 years prior to prevalence date (cumulative, the <= 10 years overlaps with the <= 5 years).
To set this up, use the Display By Time Prior to Prevalence Date section of the Statistic tab. First select whether you want to measure the Cut-Points in years or months by selecting one of those options from the drop-down list. Then specify any number of unique, increasing, integer values for the cut-points. These values must be separated by commas. Valid cut-points are from 1 to the total duration minus one, when years are selected, or 1 to (12 * total duration) - 1, when months are selected. (You specify the total duration at the top of the Statistic tab.) The time periods will be used as the inner-most row variable in the results matrix. All prevalence results include a row showing statistics for the total duration.
If you request discrete intervals, and if Multiple Primary Selection is set to "All Tumors Matching Selection Criteria", you can choose one of two possible methods for considering multiple tumors in the analysis. The two choices are:
First cancer per interval: Consider each interval separately and count the person's first tumor diagnosed within the interval's range of years prior to the prevalence date. Using this method, tumors diagnosed in two different time periods may contribute to two separate intervals. Keep in mind that the prevalence statistics for the total duration period only considers one tumor for the person. Therefore, the sum of the prevalence counts for the intervals will not necessarily equal the count for the total duration period.
First cancer over all intervals: The sum of the prevalence counts for the intervals will equal the count for the total duration period. There is no overlap among the intervals. A person is counted once toward the overall prevalence and is counted in only one interval. The person's tumor with the earliest date of diagnosis will be counted in the appropriate interval.
Please review Tumors Included in Prevalence Estimates to examine the impact of various options on the Selection tab and Statistic tab. In particular, these examples illustrate the effect of the Multiple Primary Selections when showing statistics by time prior to prevalence date.
Suppose you want to show statistics for people first diagnosed with cancer <= 3 months, <= 6 months, <= 9 months, and <= 1 year prior to the prevalence date.
Set the cut-points to Months prior to the prevalence date.
In the cut-points text field, type "3,6,9,12".
Select the option for Cumulative Intervals.
Suppose instead that you want to show statistics for people diagnosed with tumors (first or otherwise) in the periods <= 5 years, 5-10 years, and 10-25 years prior to the prevalence date.
On the Selection tab, set Multiple Primary Selection to "All Tumors Matching Selection Criteria".
Go to the Statistic tab and mark Display By Time Prior to Prevalence Date.
Set the cut-points to Years prior to the prevalence date.
In the cut-points text field, type "5,10,25".
Select the option for Discrete (Non-Overlapping) Intervals.
Select the option for First Cancer Per Interval (Intervals May Not Sum to Total).