Interaction synchrony among interlocutors happens naturally as people adapt their speaking style gradually to promote efficient communication. In this work, we quantify one aspect of interaction synchrony - prosodic entrainment, specifically pitch and energy, in married couples' problem-solving interactions using speech signal-derived measures. Statistical testings demonstrate that some of these measures capture useful information; they show higher values in interactions with couples having high positive attitude compared to high negative attitude. Further, by using quantized entrainment measures employed with statistical symbol sequence matching in a maximum likelihood framework, we obtained 76% accuracy in predicting positive affect vs. negative affect.