(#333) Re: poll

Message posted to the Speak Freely Forum
  by John Walker on Sun, 3 Aug 2003 00:05:08 +0200 (MEST).
  http://www.fourmilab.ch/wb/speak-freely.pl?rev=333

  Reply To: (#326) poll
  Author:   jean-michel
  Date:     2003-08-02 21:49

: hello i begin a poll here
: the question is :who use SF behind a NAT ?
: for me the answer is NO

For me, no also, although in the process of researching the NAT issue in the
last six months, I used Speak Freely behind a 3COM 3C16770 firewall configured
in NAT mode with static routing of ports 2074-2076 which, of course, worked
fine.

When running a poll, or any other kind of sampling study, one must take into
account selection effects. Suppose we discover that 99% of Speak Freely users
are not behind NAT boxes. What does that mean? Well, it may mean that the only
people who manage to get Speak Freely to work are those not behind a NAT box
plus those few NATted users able to set up static mappings. There's no way to
count the NATted users who haven't been able to get Speak Freely to work,
since they don't subscribe to the list nor read the forum and hence won't
reply to the poll.

I'm not making an argument here one way or another, just pointing out
something which happens all the time in science. When astronomers study the
properties of the most distant galaxies, they have to take into account the
fact that their sample is restricted to the *brightest* galaxies at that
distance, since they can't see the dimmer ones.


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