Complex sentence: Multiple studies have been performed on data from large populations of children to study the relationship between the thiomersal and autism and other neurodevelopmental disorders, almost all of which have found no association between thiomersal-containing vaccines (TCVs) and autism.
Split into simpler sentences: Multiple studies have been performed on data from large populations of children to study the relationship between the use of vaccines containing thiomersal, and autism and other neurodevelopmental disorders. Almost all of these studies have found no association between thiomersal-containing vaccines (TCVs) and autism.