The 50 states considered in this analysis encompass 18 valence states (𝜋 → 𝜋 * , 16 transitions and 𝑛 → 𝜋 * , 2 transitions), among them six exhibit a significant double excitation character, each with different contribution of the double excitations in their composition: 5𝐴 𝑔 of ethylene (20.0%), 2𝐴" (79.4%) and 5𝐴' (75.0%) of acrolein, 1𝐴 𝑔 of butadiene (75.1%), and 1𝐴 1 of cyclopentadiene (78.9%); the values in parenthesis giving the %T 1 . The 5𝐴 𝑔 state of ethylene, characterized by a high degree of double excitation, is an- ticipated to be largely affected not only by the basis set, as previously demonstrated for energies by one of us, but more importantly by the level of theory. Indeed CC3 is far from an ideal method for such genuine double excitation. The 𝛿 TPA values at that state are 894.1, 1636.7 and 1947.9 a.u. with aug-cc-pVTZ, aug-cc-pVDZ, and 6-31+G(d), respectively. These substantial differences lead us to conclude that basis sets smaller than aug-cc-pVTZ are inappropriate for accurately describing this state, prompting us to exclude this transition from further statistical analysis. The other four states display significantly smaller contributions of double excitations, and therefore they are expected to be relatively less challenging; Q-CC3 being likely well suited.