Aims: The main goal of this work is to explore which elements carry the most information about the birth origin of stars and, as such, which are best suited for chemical tagging. Methods: We explored different techniques to minimize the effect of outlier value lines in the abundances by using Ni abundances derived for 1111 FGK-type stars. We evaluate how the limited number of spectral lines can affect the final chemical abundance. Then we make an efficient even footing comparison of the [X/Fe] scatter between the elements that have a different number of observable spectral lines in the studied spectra. Results: When several spectral lines are available, we find that the most efficient way of calculating the average abundance of elements is to use a weighted mean (WM), whereby we consider the distance from the median abundance as a weight. This method can be used effectively without removing suspected outlier lines. When the same number of lines are used to determine chemical abundances, we show that the [X/Fe] star-to-star scatter for iron group and α-capture elements is almost the same. The largest scatter among the studied elements, was observed for Al and the smallest for Cr and Ni. Conclusions: We recommend caution when comparing [X/Fe] scatters among elements where a different number of spectral lines are available. A meaningful comparison is necessary to identify elements that show the largest intrinsic scatter, which can then be used for chemical tagging. Appendices are available in electronic form at http://www.aanda.org