Do you specify switch Off Resistance?
No, but the Off Resistance across a switch can be calculated using the off
leakage specifications given in the datasheet. For example: Using the +12V data
for off leakage at 85°C of the ADG5401; IOFF = 2nA (MAX) and this is measured
with +1V to +10V across the switch. Therefore: V∆ = 9V, and the minimum ROFF
is 4.5GΩ at 85degC.