How to calculate the Position Weight Matrix score?

Can anyone explain me how to calculate the Position Weight Matrix score?

I know the formula, but I don't understand it. I have a table with the frequences of nucleotides, and a table with the PWM scores:

Frequences of nucleotides:

Position:            1       2        3        4        5

A                    0       0.9      0.1      0.6      0.2
C                    0       0        0.2      0.1      0.2
G                    0       0        0.1      0        0.1
T                    1       0.1      0.6      0.3      0.5


And I have the corresponding PWM scores:

Position:            1       2        3        4         5

A                            1.848   -1.322    1.263    -0.322
C                                    -0.322   -1.322    -0.322
G                                    -1.322             -1.322
T                    1      -1.322    1.263    0.263     1


But, I have no idea how this scores are calculated. The formula is: But I don't understand this.

Can anyone explain me step by step how I can calculate this scores?

I especially don't understand how to calculate p(b,i).

Thanks! :)

• p(b,i) comes from the frequency of the nucleotide b at position i divided by the number of sequences you have taken for considering the score. This wiki page explains all need to know. – Kiritee Gak Apr 8 '17 at 13:45