290 PART 5 Looking for Relationships with Correlation and Regression

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0 2. produces a curve that’s stiff enough not to have random

wiggles (see medium, solid line). Yet, the curve is flexible enough to show that

hormone levels are fairly low until age 10, reach their peak at age 20, stay

fairly level until age 50, and then decline, with the rate of decline slowing down

after age 70. This curve appears to strike a good balance, with low bias and

low variance.

Whenever you do LOWESS regression, you have to explore different smoothing

fractions to find the sweet spot that gives the best tradeoff between bias and var-

iance. You are trying to display real features of the curve while smoothing out the

random noise. When used properly, LOWESS regression can be helpful as a way of

gleaning insight from noisy data.