Graph representations of variables

Using graphs is like drawing a map of how different factors influence each other. Each circle (or node) in our doodle is a clue (a variable), and each line (or edge) is a “this leads to that” arrow. These doodles can be as simple as a child’s stick figure or as complex as a subway map during rush hour.

For a bit of fun, let’s say we’re investigating if staying in school makes you richer. Our graph would have circles labeled Time Spent in School, Smarty Pants, Kind of Job, and Size of Paycheck. Arrows would point from Time Spent in School to Smarty Pants, and from there to Size of Paycheck (see Figure 4.3), suggesting that more school might lead to brainier brains and fatter wallets. But remember – in the twisty world of cause and effect, it’s not always so straightforward; sometimes, the plot thickens!

For our learning purposes, we can also visualize the preceding causality using a graph, as seen...