Answer: Demographic trends
Explanation: Demographic trends refers to the scope of change in the characteristics of the population such as sex ratio, age group etc.
In the given case, Jill is concerned if the demography in his target market would change into more of young people and joint family structure. Such a change would be not good for his business as the number of his potential clients will decrease.
Thus, from the above we can conclude that the given case illustrates the effect of demographic trends on the business.