# A squirrel balances a risk/benefit ratio

Squirrels and I share apples. First I begin by taking bite after crisp, juicy bite as far as my teeth can reach. Then it is the squirrels' turn. They sit up on their hind legs, in prim postures, munching every morsel. They hold one flexed paw at each end of the treat. They eat "apple on the core" the way humans eat corn on the cob.

Between us, we waste nothing. And when it comes to apple dining, we happily coexist. Yet before the squirrel portion of the feast, some hurdles must be jumped.

On one bright winter afternoon, I had placed a fresh core - I'd just enjoyed a delicious Granny Smith apple - on my deck railing about three feet from where I sat down. Sure enough, a squirrel appeared within minutes. He climbed the railing at its far end and studied me. Then he gazed at the apple core.

Jumping into an oak tree, he surveyed me and the core at closer range. Then he leaped to a maple trunk on the other side. Bright, beady eyes studied distances, angles, and probabilities. The core looked good, and he was hungry. Winter was here and pickings were slim. But I, from the squirrel's view, was a potential predator. Sunlight gleamed off his whiskers as he turned his head one way and then the other. He was calculating the risk/benefit ratio.

I had studied risk/benefit ratios in my graduate school biostatistics course and still vividly recall all those numbers and formulas. It took time, effort, and a calculator to get the answer.

The process was far simpler for my squirrel friend. Risk factors were clear: The potential predator (me), may try to catch him. The predator may succeed. Or could he escape in time? Could he grab the core and flee before I reached him?

The benefit was obvious: a fresh, juicy, and nutritious meal sitting there on the railing.

It seemed the squirrel was calculating distances and angles as well. Maybe he was also considering momentum, speed, vectors - ingredients of the physics problems I'd struggled with in college. How quickly could moving objects (or living beings) travel from one spot to another? Which one would get there first? What was the most direct route?

The squirrel gathered all his facts as he grasped the tree trunk and extended himself as far as his body could stretch. Alert eyes moved between me and the core again and again. Finally, a squirrel conclusion was reached: Too risky. Or, in statistics parlance, "risk outweighed benefit." Giving me a reproachful look, the squirrel leaped off his tree and scampered away.

It was getting cold, so I went back inside. Glancing out the window 20 minutes later, I was just in time to see a furry, gray shape leaping across my deck, apple core firmly grasped in its mouth.

Apparently, the squirrel version of risk/benefit analysis had an addendum: Wait. That which is too risky now may be perfectly safe later. With an investment of time and patience, desired benefits can be obtained somewhere down the road.

I don't know the mathematical equivalent of that rule, but it may be well worth adding to biostatistics courses.

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