That's what guarantees that people will keep buying tickets as long as the odds are in their favor.
( That ( ( 's ( what ( guarantees ( that ( people ( will ( ( keep ( buying tickets ) ) ( ( as long ) ( as ( ( the odds ) ( are ( in ( their favor ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT That)) (VP (VBZ 's) (SBAR (WHNP (WP what)) (S (VP (VBZ guarantees) (SBAR (IN that) (S (NP (NNS people)) (VP (MD will) (VP (VB keep) (NP (NN buying) (NNS tickets)) (ADVP (ADVP (RB as) (RB long)) (SBAR (IN as) (S (NP (DT the) (NNS odds)) (VP (VBP are) (PP (IN in) (NP (PRP$ their) (NN favor))))))))))))))) (. .)))
People will purchase the most tickets when they have a fifty percent or higher chance to win. 
( People ( ( will ( ( purchase ( the ( most tickets ) ) ) ( when ( they ( have ( ( ( ( a ( fifty percent ) ) or ) ( higher chance ) ) ( to win ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS People)) (VP (MD will) (VP (VB purchase) (NP (DT the) (JJS most) (NNS tickets)) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (VP (VBP have) (S (NP (NP (DT a) (JJ fifty) (NN percent)) (CC or) (NP (JJR higher) (NN chance))) (VP (TO to) (VP (VB win))))))))) (. .)))