Sol-gel and hydrothermal synthesis methods are the most sustainable processes for TiO2 nanoparticle synthesis following recent life cycle analyses (LACs). Complementary to these existing LCAs, this meta-analysis evaluates, classifies, and discusses the impact of reaction parameters on the properties of the resulting TiO2 nanoparticles. Focusing on both sol-gel and hydrothermal methods, this work analyzes the reaction conditions in spherical crystalline TiO2 nanoparticle synthesis strategies in published reports. In order to classify the impact of these reaction conditions on the crystallinity of the resulting TiO2 nanoparticles, we employed a methodology based on a local ranking (how impactful each single reaction parameter was according to the authors of the respective publications) and on a global ranking (according to average local rankings). This enabled us to uncover that the synthesis parameters' impact on the crystallinity of TiO2 nanoparticles varied in this order of reducing impact: solvent composition = presence of catalyst = solvent removal approach > synthesis method > calcination. The impact of each of these parameter categories on TiO2 nanoparticle crystallinity is then further discussed in more detail. [GRAPHICS] .