A person can do too much (or too little) of anything. The optimal amount is found where marginal cost (MC) equals marginal benefit (MB). It is a good idea to keep doing something if the MB of the next unit is greater than the MC. In fact, you keep doing it right up to where they are equal (there is a graph below to illustrate this).
So I was glad to see this article in the NY Times Sunday magazine recently: Is Screen Time Really Bad for Kids? by Kim Tingley. It discusses a study done on the effect of screen time on kids. But in addition to looking at the harms (or costs), it also mentions the benefits. One of the costs it mentions is what "they’re not doing instead" or one of economists' favorite concepts, opportunity cost (which is the value of the best foregone alternative). If you are looking at a screen you are not doing something else, like exercising or sleeping. Excerpt:
"they found that “digital-technology use has a small negative association with adolescent well-being.” But to put that association in context, they used the same method to test the relationship between adolescent well-being and other variables. And in all the data sets, smoking marijuana and being bullied were more closely linked with decreased well-being than tech use was; at the same time, getting enough sleep and regularly eating breakfast were more closely tied to positive feelings than screen time was to negative ones. In fact, the strength of the association screen time had with well-being was similar to neutral factors like wearing glasses or regularly eating potatoes.
Not finding a strong association doesn’t mean that screen time is healthy or safe for teenagers. It could come with huge risks that are simply balanced by huge rewards. “The part that people don’t appreciate is that digital technology also has significant benefits,” says Nick Allen, director of the Center for Digital Mental Health at the University of Oregon. These include helping teenagers connect with others. The real conclusion of the Nature paper is that large surveys may be too blunt an instrument to reveal what those risks and benefits truly are. What’s needed are experiments that break “screen time” into its component parts and change one of them in order to see what impact that has and why, says Ronald Dahl, director of the Institute of Human Development at the University of California, Berkeley. A screen-related activity may be beneficial or harmful depending on who is doing it, how much they’re doing it, when they’re doing it and what they’re not doing instead. “If we just respond to emotions or fears about screen time, then we actually could be interfering with our ability to understand some of these deeper questions,” he says."
The graph I mentioned is below and here is some explanation of what it means.
Marginal benefit-The additional benefit received by consuming one more unit of a good.
Marginal cost-The additional cost of producing one more unit of a good.
Suppose that the graph below shows the marginal benefit and marginal cost of some good. The best or optimal amount would be 14, where marginal benefit and marginal cost cross (where they cross is called "allocative efficiency").
Why is this the best quantity? SEE THE GRAPH BELOW. Suppose that we currently have 11 items. If we get the 12th, the cost will be 12 and the benefit will be 16. This makes sense, to spend $12 to get $16 in benefits. It makes sense to keep consuming this item as long as MB > MC. You keep getting better of as we you get closer to 14. It would be a mistake to move beyond 14, since you would be made worse off. We would give up $15 to get the 15th item while it only brought in $13 in benefits. This would make you $2 worse off.
(MC slopes upward since that is consistent with the Law of Increasing Opportunity Cost, the idea that as you produce more of a good, its opportunity cost increases. If you are giving up, say, sleep, to have more screen time, every additional hour of screen time is more costly in terms of sleep lost because 1 hour of lost sleep is not too bad, but losing a 2nd hour hurts more than losing the first hour (or if it is study time, more costly in terms of lower grades). MB slopes downward since every time you consume one more of something, your marginal or additional benefit falls, like when the first slice of pizza is better than the second and the second is better than the third, etc.)