Dear niket_sinha
I see from your profile that you have been a member since March 2008, yet I am surprised to note that you have posted this query; since it has been discussed threadbare, several times earlier.
You can RESEARCH for this topic, using the option given at the top of this page.
Also, you can browse "Similar Topics" given on the panel on the R.H.S. of this window.
A very lively discussion took place on this recently (last post on 5/12/2010) which had 33 posts :
https://www.citehr.com/300018-factor...#axzz185Vl7Pxh
I hope you will find the thread referred above, interesting and informative.
It is expected that old members would guide and help new members and freshers; rather than posting much-discussed issues.
Warm regards.