If your organization plans a reduction in force, you can rest assured that you don't have to prove that your method for selecting employees is the absolute best way to achieve your business goals.
You need to show only that your methodology is a fair and reasonable means to achieve that business goal.
Be prepared to show why your organization chose a particular method of selecting layoff targets. Example: You can use subjective supervisor assessments in addition to more objective measures. That's true even if the end result shows almost everyone in the layoff group is over age 40.
Recent case: After an upstate New York laboratory laid off 30 employees, a group of those workers sued, alleging age discrimination.
In deciding whom to lay off, the lab had used a matrix that included each employee's performance over the past two years, an assessment of their skills and how much the company needed those skills.
The employees claimed that there were better ways of obtaining the same reduction in force, such as using a hiring freeze or voluntary retirement offers.
But the 2nd Circuit said the company needed to show only that its layoff selection method was reasonable, not that there was no other way to achieve its stated goals.
Since the company's approach was reasonable and fair, it didn't matter that it affected older workers disproportionately. (Meacham, et al., v. Knolls Atomic Power Laboratories, et al., No.02-7378, 2nd Cir., 2006)
Final tip: Courts are increasingly unwilling to sit as a "super-personnel department," in such cases. Employers that do their part—by articulating legitimate business goals and reasonable means of reaching them—are unlikely to lose an age-discrimination case. The key is documenting the decision-making process as it occurs, not coming up with a rationale to fit the end result later.