The unique Paper Number assigned to each published reference in the database. For NCI/NTP bioassays, this is the Technical Report number.

Following the Paper Number, four symbols can appear which indicate details of the experiment or TD₅₀ calculation:

1. “:” appears for all NCI/NTP bioassays to indicate that TD₅₀ values have been estimated with full lifetable data.
2. “()” indicates that the standard inclusion criteria for the CPDB were relaxed for these few positive experiments. The exposure duration or experiment length was usually one week shorter than the minimum of 6 months exposure or 12 months experiment length for rodents that are required for inclusion in the CPDB.
3. “pool” indicates that the analysis uses pooled controls and that results are also included for matched controls in the plot. Pooled controls are only used in the CPDB for some early NCI experiments for which the NCI evaluation of carcinogenicity used pools because there were only a small number of matched controls.
4. “with step” appears for some recent NTP bioassays. Results for kidney were reported in the Technical Report for both the standard histopathology protocol and for results including additional sections of the kidney.