Table 2.
Summary of frequency of included variables in prognostic model development studies
| Variable | Number of models variable is included in | Combined study population of all models in which the variable is included |
| Tumour grade | 9 | 18 815 |
| Age | 8 | 17 565 |
| Tumour stage | 7 | 14 630 |
| Tumour size | 5 | 8154 |
| Gender | 4 | 12 910 |
| Carbohydrate antigen (CA) 19-9 | 4 | 1815 |
| Vascular involvement | 3 | 1059 |
| Tumour location | 3 | 6858 |
| T stage | 3 | 10 433 |
| Margin status | 2 | 774 |
| Lymph node involvement | 2 | 794 |
| Back pain | 2 | 851 |
| Carcinoembryonic antigen (CEA) | 2 | 374 |
| Lymph node ratio | 2 | 6967 |
| Co-morbidities | 2 | 1036 |
| Race | 2 | 12 136 |
| Splenectomy | 1 | 555 |
| Posterior margin positive | 1 | 555 |
| Weight loss | 1 | 555 |
| Platelet count | 1 | 50 |
| Neural Involvement | 1 | 265 |
| Neutrophil to lymphocyte ratio | 1 | 265 |
| Platelet to lymphocyte ratio | 1 | 265 |
| Albumin to globulin ratio | 1 | 265 |
| Quality of life | 1 | 219 |
| Adjuvant therapy | 1 | 219 |
| Radiotherapy | 1 | 12 136 |
| Alkaline phosphate | 1 | 218 |
| Albumin | 1 | 218 |
| Alkaline phosphate to albumin ratio | 1 | 220 |
| Geriatric nutritional index | 1 | 296 |
| Non-metastatic liver disease or insulin resistance | 1 | 296 |
| Marital status | 1 | 6400 |