The IPD provides insight to its members of their benchmark-indices in the structuring of the portfolio, in terms of allocating investments to asset classes and selecting the individual assets. These two factors are marked in general as the explanatory indicators for the achieved results in regard to the benchmark. Former research pointed out that selection has the largest impact, however, investors tend to believe that allocation is the most important factor. This research is nevertheless focused on a third ñ in practice not mentioned ñ factor, namely the interaction effect between allocation and selection. Research pointed out that the influence of the interaction effect on the return is of such an importance one cannot ignore it while making a portfolio analysis and attribution report. Therefore more attention should be paid to the aspects of structuring and building up the investment portfolio.