He later completed his PhD at the Department of Mathematics of Mons University, focusing on computational complexity in cluster analysis within Euclidean spaces.

[citation needed] His research includes the development of statistical techniques for evaluating the long-term effects of anti-diabetic drugs [2] and methods for randomized trials in addiction, psychiatric disorders, and cardiovascular diseases.

[3][4][5][6][7] He contributed to new developments of Structural Equation Modeling to assess the impact of lifestyle on aging, and menopausal effects on mood and bone loss.

[8] [9], Lehert developed predictive models In Vitro Fertilization probability of pregnancy,[10][11][12][13] and survival of extremely preterm infants.

[14] In the field of pattern recognition and artificial intelligence, he provided the first demonstration of the linear expected time O(n) complexity of clustering by connected components for any Minkowsky distances, based on cubic tessellations structures in hyperspaces.