Hello,

I have a question regarding the description and interpretation of this scatterplot especially **confidence ellipses**. We used data with volatile organic compounds (VOC) analyzed from different biological matrices (exhaled breath, serum, ruminal fluid, milk and urine).

We did a trial with cows fed hay (n=16) or silage (n=16) and wanted to discriminate the VOC profiles between the animals fed different diets and we wanted to check correlations between the VOC profiles from the different biological matrices.

Regarding the **results** in our paper I wrote:

The Pearson correlations between the VOC profiles of the different biological matrices ranged from a correlation coefficient of 0.6 (between VOC from exhaled breath and milk) to 0.98 (between VOC from ruminal fluid and urine). The VOC from exhaled breath showed the strongest correlation with those from urine with correlation coefficients ranging from 0.70 to 0.86 followed by ruminal fluid with correlation coefficients ranging from 0.69 to 0.84 , milk with correlation coefficients ranging from 0.60 to 0.76 and serum with correlation coefficients ranging from 0.69 to 0.78.

**Diskussion**

A strong correlation structure between VOC profiles from the different biological matrices were observed. The component 1 of urine and rumen fluid are good to discriminate between diets.

- Is this correct and how can I interpret “correlation structure”? What exactly means this term?

**What can I improve and how can I describe and interpret the confidence ellipses?**

Thank you in advance

Julia