The Yule-Nielsen effect, also called optical dot gain, has often been modeled based on convolutions between halftone dot patterns and a point spread function, PSF, characteristic of the paper. The form of the PSF is generally assumed or measured empirically. An alternative approach to modeling the Yule-Nielsen effect employs a probability function P_p, which describes the fraction of reflected light emerging between halftone dots and under dots. The probability model is shown to fit experimental data on the Yule-Nielsen effect quite well. Moreover, the model can be implemented with simple algebraic expressions rather than the convolution or Fourier calculations required for PSF models. In addition, the quantitative relationship between P_p and PSF is demonstrated.