we analyze 14 world studies about the ductility resistance reduction factor , and other four developed in the scientific research centre at the army polytechnic school by aguiar and guerrero at 2006, by aguiar and gonzález at the same year, and by aguiar, romo y aragón at 2007, and we make a comparative analysis. the first work it？s based on 63 registers of 15 earthquakes registered in colombia, peru, chile and argentina with soil acceleration 15% over gravidity acceleration, but these registers are not classified by soil type. the results obtained are compared with nassar and krawinkler research published at 1991, and with miranda research published at 2000, both of them worked with united states of north america registers. the results are very approximated even when we used earthquakes registers from different countries. in the second one, we generated 28 artificial earthquake registers, which reproduce in an approximated way, the elastic design spectrums provided by the ecuadorian construction code, cec-2000 for the four soil profiles stipulated in the code for the highest seismic danger zone. in the third one, we obtained the ductility seismic forces reduction factor from 80 earthquakes registers from ecuador with soil accelerations 10% smaller than gravidity acceleration and 112 artificial earthquake registers compatible with the cec2000 elastic design spectrums for the four seismic danger zones in our country. we obtain with chopra 2005 procedure. the final work is an extension of the third one, and presents a more general and easier to use equation that combines the three previous works.