if Z is less than 1 then it is showing negative deviation from ideal behaviour.???why please explain the statement

A gas which obeys the gas laws and the gas equation PV = nRT strictly at all the temperatures and pressures is called as ideal gas.However no real gas strictly obeys the ideal gas laws at all the T and P and deviations from ideal behaviour is observed particularly at high pressures and low temperatures.In case of real gas such deviation from ideal behaviour can be measured in terms of compressibility factor which is denoted by Z.Mathematically this Z is given as -
Z = PV/ nRT
Thus for ideal gas, Z = 1 for all T and P
But in case of real gas,
Z 1
This Z would be either less than 1 or greater than 1.
if Z < 1 ,then gases shows negative deviation from ideal behaviour.So
PV < nRT.When we replace nRTby PV_ideal we get,
PV_real < PV_ideal
or,
V_real < V_ideal
This implies that the gas will be more compressible than that expected from ideal behaviour.This shows the predominance of attractive forces.For ex- gases like CO2 ,CH4 nad N2 are more compressible at low pressures and show negative deviation.