By how much did Elly Koss's weight increase from the observation in 2008 to the observation in 2009?
SUBTRACT((DATE like '2009%'), (DATE like '2008%')) where DESCRIPTION = 'Body Weight';
SELECT SUM(CASE WHEN strftime('%Y', T2.date) = '2009' THEN T2.VALUE END) - SUM(CASE WHEN strftime('%Y', T2.date) = '2008' THEN T2.VALUE END) AS increase , T2.units FROM patients AS T1 INNER JOIN observations AS T2 ON T1.patient = T2.PATIENT WHERE T1.first = 'Elly' AND T1.last = 'Koss' AND T2.description = 'Body Height'