A key hospital outcome measure of clinical performance is length of stay $($LOS$),$ that is$,$ the number of days a patient is hospitalized. For patients at one hospital with acute myocardial infarction $($heart attack$),$ the length of stay over the past four years has consistently decreased. The hospital also has data for various treatment options such as the percentage of patients who received aspirin upon arrival and cardiac medication for Left Ventricular Systolic Dysfunction $($LVSD$).$ The data are as follows:

Year Average LOS Aspirin on arrival LVSD medication

$20074\mathrm{.}24$ days $92\%89\%$

$20084\mathrm{.}11$ days $98\%92\%$

$20094\mathrm{.}13$ days $98\%96\%$

$20104\mathrm{.}10$ days $100\%98\%$

Found Y and X Correaltions: LOS, Aspirin, LVSD

LOS Aspirin

Aspirin Y

LVSD X