Gas extraction from the Groningen gas field resulted in significant induced seismicity. We analyze the magnitude-frequency distribution of these earthquakes in space, time and in view of stress changes calculated based on gas production and reservoir properties. Previous studies suggested variations related to reservoir geometry and decreasing b-value with increasing Coulomb stress. While we confirm the spatial variations, we do not detect a clear sensitivity of b-value to Coulomb stress. However, we find that b-value correlates positively with Coulomb stress rate. This correlation is statistically significant and robust to uncertainties related to stress calculation. This study thus points to a possible influence of stress rate on the magnitude probability of induced earthquakes.