Hi,

I have a data set on tumors with the variables karnofsky index/KI (categorical with values 40, 60, 80, 90, 100) and gross tumor volume/GTV (continuous, m3), among others. I have done a linear regression showing a significant negative correlation between the two (coefficient -0.16, p 0.007).

1. I want to visualise the relationship, f.eks with a scatter plot, but as KI is categorical and GTV is continuous, it ends up looking very strange and I cannot see a linear relationship. I have transformed the GTV variable with cube root because it was very left-skewed, but KI has a normal distribution. Do I still have to transform KI to get a linear relationship?Or convert it to a continuous variable?

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2. I want to calculate the Pearon's correlation coefficient, but as far as I know assumptions are that the variables must be continuous and have a linear relationship. How do I solve this? By transforming one or both values?

Thanks in advance,
Best regards