My Thanksgiving ritual each year consists of heaps of turkey, corn casserole and apple pie — as well as quiet time devoted to helping relatives choose Medicare prescription drug plans for the following year.

Most people partake in similar gorging, but not enough spend the time to compare health plans for their relatives. My experience this past weekend is a particularly instructive example of how costly it can be to do nothing.

Unlike Medicare's hospital and doctor benefits, which are managed by the federal government, seniors and disabled people needing drug coverage must choose a subsidized, privately run plan under contract with Medicare. The 36 million enrollees in the program usually have dozens of choices that offer an array of monthly premiums, deductibles and copayments. The plans have different preferred drugs and different requirements for prior approval for expensive generics.

Depending on the drugs each person takes, some plans are much cheaper than others.

Sounds good so far, but there's a giant catch: Once a person signs up for a plan, his or her enrollment continues from year to year if the person does nothing — even if the plan raises its prices and tightens its requirements. It’s up to enrollees to determine if there’s a better choice, and they can switch plans once a year (during open enrollment).

Consider my in-laws, who live near Dallas.

Last year, I helped them pick a pretty awesome plan that cost each of them $31.10 per month. It has no drug deductible, meaning they didn't have to pay out of their pockets before their drug coverage began. And generic drugs cost them nothing. Both only take generic drugs — several of them, mind you — and their annual drug costs were less than $375.

But if they had chosen to stay with their plan for next year, prices would have exploded. Their monthly premium would have increased to $47.10 and they would have had drug co-pays of at least $3 per prescription. When you add it all up, my mother-in-law's annual costs would have more than tripled, to $1,146, and my father-in-law's would have increased to $1,086.

That’s a steep price for doing nothing.