In 1990, the incidence of bone fractures  was very high among people over 70 years old in W city, and at the same time, the mortality rate of people over 70 years old was also very high, so it can be known that the high incidence of bone fractures  led to an increase in mortality among people over 70 years old.
The statement 'Many people over 70 years old in W city are living alone' most weakens the above argument.