http://jamanetwork.com/journals/jamainternalmedicine/article-abstract/2610103

Question  What is the effect of heightened vigilance during unannounced hospital accreditation surveys on the quality and safety of inpatient care?

Findings  In an observational analysis of 1984 unannounced hospital surveys by The Joint Commission, patients admitted during the week of a survey had significantly lower 30-day mortality than did patients admitted in the 3 weeks before or after the survey. This change was particularly pronounced among major teaching hospitals; no change in secondary safety outcomes was observed.

Meaning  Changes in practice occurring during periods of surveyor observation may meaningfully improve quality of care.