In evaluating motions for summary judgment under employment discrimination laws, such as the Age Discrimination in Employment Act, must a court examine all the evidence together to determine whether a reasonable jury could find discrimination by a preponderance of the evidence (as required by the Seventh Circuit), or must the court apply a special heightened standard of proof that separately evaluates different pieces of evidence based on the "stage" of the inquiry or on whether the evidence is "direct" or "circumstantial" (as required by the Eleventh Circuit, among others)?

What standard of proof must courts apply in evaluating summary judgment motions in employment-discrimination cases?