Complex sentence: Over the course of several years scientists determined that Chelsea had average intelligence, with her IQ regularly measured between 77 and 89, and found her cognitive profile consistently fell within the 9 to 10 year old range.
Split into simpler sentences: Over the course of several years scientists determined that Chelsea had average intelligence, with her IQ regularly measured between 77 and 89. Throughout the time scientists worked with Chelsea, her cognitive profile consistently fell within the 9 to 10 year old range.