show work Sales Unit year over year Increase$/$Decrease $($Jan vs Jan, etc.$)$

Jan $25\%$

Feb $26\%$

Mar $25\%$

Apr $-4\%$

May $-7\%$

June $-10\%$

$1.$ What are possilbe causes for the decrease in year over year sales starting in April?

$2.$ What data would you want to be able validate the possible causes?