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Behavior over time (BOT) graphs are another important tool in systems thinking. With a BOT you can show how a variable changes over time. The basic elements of any BOT are a horizontal time axe,axis, and the vertical axeaxis showing the value of a variable. BOT graphs are drawn in order to explore patterns of behavior. This is as important as understanding cause and effect relationships through drawing causal loop diagrams. When thinking about cause and effect, we should not eliminate all the transitions between the two. Kirkwood suggests,suggests that patterns of behavior (as reflected in BOT) should be explored before considering a systemssystem's structure. This means that BOT should be developed for different variables that are relevant for the problem you are trying to understand. “[O]nce you have identified a pattern of behavior that is a problem, you can look for the system structure that is known to cause that pattern.”[1]

Behavior over time graph

In order to see how variables patterns of behavior over time differ from each other, you can also graph more than one variable in one BOT graph. You can then also combine causal loops with BOT.BOT graphs.

Let us think of an example we used earlier: the inter-relationship of anxiety at work and number of mistakes made. An employee in a small firm realizes that he is anxious at work, for a while he has not been feeling so good at work and now he feels sick in mornings, starts sweating, etc. He has made a couple of mistakes at work as well and they have been noticed by his supervisor and co-workers. In a conversation about his feelings, one of his colleagues asks him to draw a graph of how his anxiety has changed in the last year as well as when he has started to make mistakes.

Behavior over time and causal loop

In the BOT, we can clearly see that both variables are reinforcing themselves in the paragraph. We can see in the graph as well that anxiety increased before the number of mistakes – the increase in mistakes iswas therefore first a result of anxiety before it becomesbecame a reinforcing factor for anxiety. The increase in anxiety ismust therefore be linked to other system structures as well.

References and resources:
Kirkwood, Craig W., System Dynamics Methods: A Quick Introduction, 1998, p. 3. < http://www.public.asu.edu/~kirkwood/sysdyn/SDIntro/ch-1.pdf> (accessed 13 August 2009)

Quaden, Rob/with Lyneis, Debra, Drawing and Reading Behaviour over Time Graphs. Four Maths Lessons to Build Graphing Skills, Acton, MA, 2000. <http://www.clexchange.com/ftp/documents/Math/MA2000-10GraphingSkills.pdf> (accessed 12 August 2009)

WikiSD, Behavior Over Time Graph <http://www.systemdynamics.org/wiki/index.php/Behavior_Over_Time_Graph> (accessed 12 August 2009)

Stamell, Gene/with Lyneis, Debra, Everyday Behavior Over Time Graphs, Acton, MA, 2001. <http://www.clexchange.org/ftp/documents/x-curricular/CC2001-11EverydayBOTGs.pdf> (accessed 14 August 2009)

"Behavior over Time Graphs" <http://www.pegasuscom.com/botgraphs.html> (accessed 12 August 2009)

Notes:
[1] Kirkwood, Craig W., System Dynamics Methods: A Quick Introduction, 1998. < http://www.public.asu.edu/~kirkwood/sysdyn/SDIntro/ch-1.pdf> (accessed 13 August 2009)