Based on these facts, we suggested that middle-aged adults were enjoying higher SQOL when they were younger and in shorter duration of marriage, had higher social and economic levels and more frequent sexual intercourse. However, concerning education level and gender, the results of each study had some differences. Therefore, it is necessary to conduct more in-depth follow-up studies to identify the reasons why these differences exist. On the other hand, the subjects of this study felt lower SQOL when they lived with their spouse alone than those that lived with their children together.