- User Guide and Online Help
- Initiate and monitor data mining runs
- Create a Data Mining Run
- Reference
- Use the PRR calculator
Use the PRR calculator
When creating a data mining run, you can specify that Proportional Reporting Ratio (PRR) and Chi-square should be computed and included in the results for each drug-event combination against a specified background database.
Before you use the PRR calculator, you must specify three case series (based on the same configuration) to represent a background database, the events of interest, and the drugs of interest. For example, to compute PRR for combinations of analgesics and respiratory ailments in women over age 65, use a case series that includes cases for women over age 65, a case series that includes cases for analgesics, and a case series that includes cases involving respiratory ailments.
- Click the Case Series page.
- On the Case Series page, identify or define the three case series to use.
- Click PRR Calculator.
- From the Configuration drop-down list, select a data configuration.
- For the following types of case series, click Browse and select a case series. You must base all three case series on the same configuration.
- Background Definition Case Series—Defines the customized background for the computations.
- Event Definition Case Series—Defines the set of events.
- Drug Definition Case Series—Defines the set of drugs.
- To define the chi-square calculation method, check or clear Apply the Yates correction for chi-square.
- To define the PRR calculation method, check or clear Include drug of interest in the comparator set.
- Click Calculate.
The observed counts and results appear.
- Observed counts of cases with drug-event combinations are represented as a, b, c,
and d in a 2x2 table as follows:
Note:
When PRR is computed by a data mining run, a, b, c, and d represent counts of drug-event combinations by default. You can select an option to count cases with those combinations instead. However, the PRR calculator always counts cases.Observed counts of cases with drug-event combinations are represented in the 2x2 table as follows:
Cases Specific drug All other drugs Specific event
a
b
All other events
c
d
- The PRR for the combination of a particular drug and particular event is computed as follows:
- PRR = (a / (a + c)) / (b / (b + d))
- If b=0 (and Include drug of interest in the comparator set described below is cleared), then the formula is adjusted as follows to avoid the possibility of division by zero:
- PRR = ((a+0.5) / ((a+0.5) + (c+0.5))) / ((b+0.5)/((b+0.5) + (d+0.5)))
- If you checked Include drug of interest in the comparator set, the application computes PRR as:
- PRR=(a / (a + c)) / ((a + b) / (a + b + c+ d))
For each cell in the 2x2 table, the expected count is computed as follows:
Cases Specific drug All other drugs Specific event
E(a) = ((a+b)(a+c))/(a+b+c+d)
E(b) = ((a+b)(b+d))/(a+b+c+d)
All other events
E(c) = ((c+d)(a+c))/(a+b+c+d)
E(d) = ((c+d)(b+d))/(a+b+c+d)
The chi-square of PRR (PRR_CHISQ) for the combination of a particular drug and particular event is computed as follows, where E represents the expected count under the assumption of no relationship between drugs and events:
- PRR_CHISQ = ((a-E(a))2)/E(a)+ ((b-E(b))2)/E(b)+ ((c-E(c))2)/E(c)+((d-E(d))2)/E(d)
If you checked Apply the Yates correction for chi-square, PRR_CHISQUARE is computed as follows:
- PRR_CHISQ = ([max(0, |a - E(a)| - 0.5)]2)/E(a) + ([max(0, |b - E(b)| - 0.5)]2)/E(b) + ([max(0, |c - E(c)| - 0.5)]2)/E(c) + ([max(0, |d - E(d)| - 0.5)]2)/E(d)
Note:
|a - E(a)| = |b - E(b)| = |c - E(c)| = |d - E(d)| for every 2x2 table; this formula can also be expressed as:
PRR_CHISQ = (1/E(a) + 1/E(b) + 1/E(c) + 1/E(d)) [max(0, |a - E(a)| - 0.5)]2
The P-values for chi-square values are also computed. The P-value is the probability that chi-square would be as large as the value for PRR_CHISQ by chance alone if there were no causal relationship or consistent association between the drug and the event.
Note:
If any of E(a), E(b), E(c), or E(d) is zero, the chi-square and P-value cannot be computed and are defined arbitrarily as -1. - Observed counts of cases with drug-event combinations are represented as a, b, c,
and d in a 2x2 table as follows:
- In the table for observed counts, you can click the value of N in a column to display a menu. Click View Cases to drill down to cases that have the specified drugs and specified events.
Parent topic: Reference