One historical example of the difference-equals-deficit error is

One historical example of the difference-equals-deficit error is that children who are hearing impaired cannot communicate as well as children who can hear just fine. This is a common assumption most people think, that those who do things different than the norm is incorrect. Because it's different, it becomes an error in our mind that they are less capable of doing things. 

The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.