<p>Here, the abundance measure can represent concentration, molecular number or ppm, not in the chip-matter.</p>

<p>I don't know why to log them in the classification or regression model as y variable?</p>

<p>Could anybody help me? Thank you.</p>

<p>Apart from symmetry-fying the increase/decrease scale, I think taking logarithm makes the distribution gaussian(ish) for which you can do parametric tests, taking log also to some extent, takes care of heteroscedasticity (non-uniform mean dependent variance)</p>
