Hosoya Z Index and Correlation with Boiling Point
For a given hydrocarbon C$_n$H$_{n+2}$ more branched hydrocarbons have lower boiling point. This is because they have less surface area to have Van der Waals interactions to entangle with each other (ropes have more chances to entangle with each other than balls). For example C(CH3)4 (n-pentane) is a gas, but all other pentanes are liquids. 

Their method is qualitative only. For instance, o-p-nitrophenol can be steam distilled and has much higher vapor pressure at a given temperature than p-nitrophenol, but the table would predict that they have the same properties. The difference is due to intramolecular h-bond present in o-, but ansent in p- isomer.