A statistical analysis of all the published experimental data on the wavenumbers of rovibronic optical transitions of the D₂ molecule was performed for the first time. We used the optimization method of analysis (B.P. Lavrov and M.S. Ryazanov, JETP Lett. 81 (8), 371 (2005)), which allowed experimental errors to be estimated independently. 3588 of 3822 data (=94%) obtained by different methods in different works were found to be in excellent agreement with each other. It was shown that these data can be divided into 19 groups of uniformly precise experimental results. Experimental errors were determined for each of these groups. This created prerequisites for obtaining optimal energy values for all the triplet rovibronic states of D₂ studied experimentally. 234 data (for 228 lines) were found to be in strong contradiction with the others according to the Rydberg-Ritz combination principle. Additional experimental studies of the doubtful spectral lines are necessary.