Option 1: Growth rate of population is not determined by the difference between male and female growth. It is about overall population growth, regardless of gender.

Option 2: Growth rate of population is not about the difference between urban and rural areas. It focuses on the overall population growth, regardless of the geographic location.

Option 3: The number of births per thousand people is not the definition of growth rate of population. It is a measure of birth rate, which is related to population growth but not synonymous with it.

Option 4: Correct answer. Growth rate of population is calculated by comparing birth rate and death rate. A positive difference between birth and death rates indicates population growth, while a negative difference indicates population decline.

Therefore, the correct answer is option 4.