It should be mentioned that the credits currently are VERY small - probably only resulting in rounding upped/downed zeroes here at BOINCstats - and that this probably will change in the future.
Rounded up zeroes would imply negative values, this is not the case.
these were the team stats a few days ago:
MariaDB [dcfree]> select id,team,metric1 from boinc_team where proj = 'ith' order by metric1 desc;
+------+------------------------+----------+
| id | team | metric1 |
+------+------------------------+----------+
| 1 | SETI.USA | 0.0611 |
| 2009 | BOINC@Ukraine | 0.054953 |
| 864 | BOINC@Taiwan | 0.027267 |
| 3 | L'Alliance Francophone | 0.025777 |
| 101 | [H]ard|OCP | 0.022313 |
| 98 | AMD Users | 0.01845 |
| 1481 | Aggie The Pew | 0.01811 |
| 45 | BOINCstats | 0.013107 |
| 1027 | Overclock.net | 0.010937 |
| 2012 | Team-Goobee.org | 0.01031 |
| 121 | Free-DC | 0.006717 |
| 70 | Rechenkraft.net | 0.005723 |
| 141 | Team Norway | 0.005643 |
| 2010 | BlackOps | 0.005607 |
| 142 | BOINC@Poland | 0.002767 |
| 33 | OcUK - Overclockers UK | 0.00273 |
| 237 | BOINC Confederation | 0.00068 |
| 47 | BOINC@Heidelberg | 0.000587 |
| 2011 | Hardware Canucks | 0.00044 |
| 211 | USA | 0.000213 |
| 978 | gigo | 0.000137 |
+------+------------------------+----------+
21 rows in set (0.01 sec)
As you can see all positive values, which were rounded down to zero -I'd multiply them with 10000 to give them all a value of 1 or more.