it depends on whether the data forms a normal distribution or a...

it depends on whether the data forms a normal distribution or a skewed distribution. If it's a normal distribution, then half the data would have to be above the mean, and half would be below the mean, but not if it's a skewed distribution. Only if STX were referring to the median porosity, not the mean, would half the data have to be above the median and half below, in both a normal and a skewed distribution. In any case, there is both an upper bound of 100 and a lower bound of 0 in terms of porosity, so the example above of a porosity of 111 is invalid. It is simply not possible to have a porosity greater than 100%, nor a porosity of less than 0.