As we know, computational techniques are complementing the more traditional approaches of measurement and analysis. I would like to know if there is any technique that its result could be compared with experimental data.
It depends on your problem geometry under discussion. If its 1D or 2D u can do it very easily with some online calculators or with simple formulae available in literature. If its complex 3D structure then you should go for CST or HFSS software.
Mr Anurag Misra has rightly suggested. There are data available for various material/structure through which, when EM energy passes how much is the attenuation. It can be calculated easily, as case may be
CST Microwave Studio or Ansys HFSS will be the most obvious choices to correlate simulations with measurement data. You could also use Nimbic nWave from Mentor Graphics if you are trying for EMI shielding of IC packages.