Data and question

Hazard ratios for the association between Mediterranean Diet Score and ovarian cancer Mediterranean Diet Score 5.5 P trend N cases 134 119 148 136 159 Person-years 290,089 247,467 329,112 293,048 309,867 Age-adjusted hazard ratio 1.0 (ref) 0.91 0.85 0.86 0.93 0.52 Multivariable- adjusted hazard 1.0 (ref) 0.90 0.83 0.85 0.91 0.44 ratio 9. Examine the results in the table above. Suppose that a Mediterranean diet truly reduces the risk of ovarian cancer. What sources of bias most likely accounted for the null or nearly null findings