If you get assigned to a task with an estimate you did not yourself, and you feel the estimate is not accurate, send the following email:
Your boss is named Harry, and the guy that estimated the task is called Snoopy.
Subject: Regarding task #XXX
estimations
Dear Harry,
I've been assigned to work on the task #XXX. I noticed that the
estimations was made by Snoopy.
I feel unconfortable with that estimation and I can't commit I will
be able to do it in that amount of
time.
I suggest that Snoopy do the task instead as he seems to be
able to do it in less time than me.
I have a suggestion to avoid such situations. Why not using Planning
Poker to do estimates? Planning Poker
is a consensus-based technique for
estimating.
It is a technique that minimizes anchoring by asking each team member
to play their estimate card such that
it cannot be seen by the other
players.
The meeting proceeds as follows:
Planning Poker is a serious issue, not
a game. But when you introduce
Planning Poker Cards at your next
release planning meeting, team
interest level (and participation)
will shoot straight up and, even
better, you'll walk away with what is
most likely the most accurate project
time estimate you've ever had. Here's
how it works...
You create your required feature list as usual. Your Scrum Backlog for
example.
The most experienced developer (or the Scrum Master) for each feature
provides an overview of the
functionality for that feature. Team
members can ask questions and
participate in discussions until the
feature has been fully discussed. No
one is allowed to mention time
estimates during the discussion. The
Product Owner makes a note of the
final consensus.
Each team member selects a Planning Poker Card representing their estimate
of the amount of time (usually Story
Points or Ideal Days) required to
produce that feature and lays it on
the table face down. Again, time
estimates are not permitted to be
mentioned out loud.
Everyone turns their cards over at the same time.
Team members with high and low estimates are given the opportunity to
make their case for supporting the
amount of time they have estimated.
The process is repeated until the team reaches a consensus. Preference
may be given to the estimate of the
developer who will be responsible for
implementing the feature in question,
but the Product Owner, acting as
moderator, should help in the
negotiation.
A timer is used to ensure that each discussion phase does not drag on. The
moderator or Project Manager controls
the timer. Once the allotted
discussion time has passed, another
round of Planning Poker ensues.
The entire process forces each team
member to fully think out their
position and to be able to present
their justifications to the team. No
one has more authority than anyone
else, and the project time line is
developed without pressure or bias.
Check this out. (disclaimer: I'm the owner of that website)
Companies like Microsoft, Google, Ebay, Nokia are using that methodology. Why not you?