A Stock-and-Flow Diagram

A chronic problem of the college student is staying awake. A healthy amount of sleep consists of 6 to 8 hours, but because it has  to be penciled into hectic schedules, it seems that no one ever gets enough sleep.

This stock-and-flow diagram illustrates the effects of stress on how awake a person feels during the day. The amount of sleep (the inflow), affects how awake a person feels (the stock), which is released by ability/capacity to function during the day (the outflow); however, this basic process is affected by many more variables.

How much stress a person experiences during the day influences how much sleep they desire in order to be more awake. The discrepancy between this desired level and the actual level of awakeness leads a person to take naps in order to gain more sleep. This loop is called a balancing feedback loop (denoted by the B)  because, according to Donella Meadows, it “opposes whatever direction of change is imposed on the system” (28) in order to maintain relative stability. In this case, the loss of sleep is opposed by the desire to sleep more by napping. Another balancing feedback loop is that stress causes the body to address the discrepancy between normal levels and stressed levels by producing adrenaline. In other words, adrenaline augments the level of awakeness by increasing the body’s ability to function during periods of stress. Then again, too much stress can lead to fatigue.

What this diagram ultimately reveals is that there exist relationships that are not easily seen at first. Variables such as stress can influence the flow of a system in more than one place. Think of mountain runoff into a river. Water from one single peak can flow into multiple sections of a river below, influencing it from beginning, middle, to end.

Now, time to get some sleep.

(What we all need in the A-school: a sleep suit)


One thought on “A Stock-and-Flow Diagram

  1. zuangster says:

    I agree with your first B feedback loop showing how the lack of sleep is opposed by the contrasting desire/requirement to regain hours of rest by napping during normal waking hours. However, your loop also suggests that in the additional situation where someone has too much sleep, the resulting feedback loop is one implies not sleeping/taking naps during the day in an attempt to level off to the traditional 6-8 hours of shut eye. I was curious if this made sense, considering how some individuals who sleep way more than average, then to still nap for long periods of time, regardless of time. How about if the 6-8 hours of sleep occurred on a delayed schedule of 4AM-10AM/12PM; does the timing of hours have any influence on your diagram?

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