Mark Needham

Thoughts on Software Development

Feedback Loops: Human Decisions

without comments

I’ve been reading Donella Meadows’ ‘Thinking In Systems: A Primer‘, an introductory text on systems thinking, and after 30 pages or so the author poses the following challenge:

Sometimes I challenge my students to try to think of any human decision that occurs without a feedback loop – that is, a decision that is made without regard to any information about the level of stock that it influences

Meadows has quite a nice way of guiding us to thinking about systems by referring to ‘stocks’ and ‘flows’.

A stock is the foundation of any system. Stocks are the elements of the system that you can see, feel, count, or measure at any given time. A system stock is just what it sounds like: a store, a quantity, an accumulation of material or information that has built up over time.

Stocks change over time through the actions of a flow. Flows are filling and draining, births and deaths, purchases and sales, growth and decay, deposits and withdrawals, successes and failures.

For example the following diagram represents the flows into and out from a water reservoir:


The ‘water in reservoir’ is the stock in this system while rain/river inflow act as the in flows and evaporation/discharge are the out flows.

This is a reasonably simple example because it doesn’t show any of the factors in the system which might impact the in flows or out flows of the system.

I talk with friends of mine reasonably frequently on instant messenger so I thought it’d be interesting to try and see how that system would fit into this model:

Im conversations

The curved arrows in the diagram are known as information links and they direct the action in the system.

In this example we have “desired knowledge level” and “knowledge of friends’ lives” which are compared to each other and lead to a discrepancy which can be fixed through instant messenger conversations which increase the ‘communication with friends’ in flow.

I think the ‘stock’ in this system is the desire to know more about what my friends are up to but I’m sure there are other ways of looking at this relationship as well.

It feels a little bit ‘unhuman’ to think of things in terms of stocks/flows and I’m doubt most people think about stock levels consciously when deciding to have a conversation! The feedback loop is much more implicit.

When discussing this with Sat he pointed out that in a more accurate systems diagram there would also be other feedback loops which might include how busy we are, how interesting the conversation is, how tired you are and so on.

The book does get onto that but I hadn’t realised that such a simple human decision was in fact being influenced by a feedback loop!

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Written by Mark Needham

May 5th, 2011 at 6:04 pm