Guidelines for specifying drugs for logistic regression

For a logistic regression run, you define the number of predictor values (that is, how many drugs) to include in computations for each of the events you select for the run. You also define the minimum number of reports in which a selected event must occur in combination with a drug for that drug to be included. Optionally, you can supply a list of drug values to include in the run.

Using these values, the Oracle Empirica Signal application determines what drugs to include for each event in the run, including any explicitly specified drug values and selecting additional drugs that occur in combination with each run event frequently, based on the defined total number of drugs and the minimum number of occurrences.

• If you explicitly specify fewer drug values than the defined total number, the application finds additional drugs in the configuration to make up the difference. The application uses the defined minimum to limit the possible set of drugs to include in the run to those found most frequently in combination with each of the selected run events. For each event, only drugs found in combination at least that number of times are included.
• Each of the drug values that you explicitly supply are included in the run, even if they do not meet the specified minimum for a given run event. (However, the drug+event combination must occur at least once to be included.) If you supply more drug values than the defined total number to include in the run, the Oracle Empirica Signal application orders the drug values alphabetically and includes only the first <total number> from the list.

For example, assume that you specified a single event, Rash, for the logistic regression run. You keep the default, 10, as the minimum number of cases in which the drugs must occur, and you explicitly include DrugD. The following table lists sample drugs in the data configuration, the number of occurrences of Rash, and whether the run computes scores for the drug:

Drug	Number of Cases in which Drug Occurs in Combination with Rash	Whether the run computes scores for the drug
DrugA	11	Yes
DrugB	10	Yes
DrugC	5	No
DrugD	1	Yes
DrugE	0	No

Oracle recommends that you include drugs that occur most frequently with an event, as computational biases can result if they are left out. For more information, see Logistic regression computations.