How to normalize pwelch output and calculate band power using it ?

Hello ,

I am using , [pxx,f] = pwelch(x,window,noverlap,f,fs) , to compute power spectrum of a EEG signal .

I have to calculate band power in 1Hz frequency bands in 4-30Hz , using Hamming window , with 50% overlapping . I have 4 seconds of EEG data sampled at 250 Hz . In order to calculate the band power , say in 4-5Hz frequency band , I am using the following code : [pxx,f] = pwelch(data,[],[],[4:0.01:5],250) . So , i compute PSD at 100 frequencies points in the desired frequency band , and add each one to get the area under this band .

My questions are :

1.Is the way i'm computing the band power in each band , correct?

2.As per Matlab's documentation , "The units of the PSD estimate are in squared magnitude units of the time series data per unit frequency. For example, if the input data is in volts, the PSD estimate is in units of squared volts per unit frequency. For a time series in volts, if you assume a resistance of 1 Ω and specify the sampling frequency in hertz, the PSD estimate is in watts per hertz." . How do i normalize this Pxx?....What frequency should i multiply it with ?

Any help would be greatly appreciated .

Vinayak