I want to investigate significant predictors for disease free survival. For this, I did created Kaplan Meier curves for each possible risk factor. The significant predictors after Kaplan Meier analysis were included in a Cox regression analysis.
Tumor diameter (divided in 3 categories) was a significant predictor after Kaplan Meier analysis. Category 1 had a mean of 95.435, category 2 had a mean of 85.078, and category 3 had a mean of 64.382. The curves were plotted as expected: category 1 had the highest disease free survival, followed by category 2. Category 3 had the lowest disease free survival. After cox regression analysis however, tumor diameter remained a significant predictor, but the hazard ratio was 0.010 for group 2 compared to group 1.
Can anyone give an explanation on why the cox regression analysis predicts a significant higher disease free survival with increasing tumor diameter, while the kaplan meier analysis shows a decreased disease free survival with increasing tumor diameter?