Mutual funds, Panel data

[tarox]

Dear all,

my study is about evaluating mutual funds s from Jan 2003 to Jul 2014 and some mutual funds did not establish in same year or even month it is about 62 funds i have Nat asset value my steps are

1- sum all Nat for all funds at every month and make one column of Nat
2- find the returns by R=(Nat 2-Nat1)/Nat1*100 or LN R=(Nat2/Nat1)*100

my questions are :(
1- How could i sum the Nat for all funds to make it just one column
2- how should i know which method to use to find the returns R=(Nat 2-Nat1)/Nat1*100 or LN R=(Nat2/Nat1)*100

thank you

[tarox]

No one ??