[en] The shapes of the ground-state transitions of ⁴²K, ¹⁴²Pr, ⁸⁶Rb, and ⁹¹Y were carefully measured in an intermediate-image β ray spectrometer. The spectra were analyzed using exact electron radial wave functions of Bhalla and Rose. The measured shapes were compared to the theoretical predictions in terms of a linear fit of the form (1 + aW) and a hyperbolic fit of the form (1 + b/W). All the spectra were found to show a small order deviation from the simple unique shape. The shape factor term in the analysis of ⁹¹Y was found to be b = +0.027 plus-or-minus 0.007. Some of the existing theoretical approaches in this direction have been discussed. (U.S.)