Project Blue Book Special Report (second copy)

In five of the six cases, the probability is less than 1 per cent that
the distributions are the same. In the sixth case, Light Brightness, the
classifications are too nebulous to be of real value. However, these tests
do not necessarily mean that the UNKNOWNS are primarily "flying saucers"
and not aircraft, balloons, or other known objects or natural phenomena.
The UNKNOWNS might still be unidentified KNOWNS if either of the follow-
ing cases occurred:
(1) The characteristics which were observed for the UNKNOWNS
were different from those observed for the KNOWNS because
of the psychological make-up of the observer or because of
atmospheric distortion. This assumes the distribution of
objects in KNOWNS and UNKNOWNS is the same.
(2) The UNKNOWNS may be known objects in different propor-
tions than the group identified as KNOWNS. (That is, a
greater percentage of the UNKNOWNS could be aircraft
than the percentage of aircraft in the identified KNOWNS.)
The second case is the more probable one. In this connection, it is
interesting to note the factors which contributed to a large chi square
result in the tests made above:
(1) Color
The major contribution to chi square in color is from the
color green. There is a large excess of green sightings
among the KNOWNS over the UNKNOWNS. Of the 130
known objects in this classification, 98 are astronomical,
and are due mostly to the green fireballs reported from
the Southwest U. S.
(2) Number
The large chi square is due to a greater proportion of
UNKNOWNS in the multiple object classification. Apparently
these are harder to identify.
(3) Shape
In this case, there is a higher percentage of UNKNOWNS
in the rocket-aircraft-shape classification. These might
be familiar objects for which unusual maneuvers were
reported. .
There is a higher percentage of KNOWNS in the flame
and in the meteor- or comet-shape category, which in
both cases appears to result mainly from excesses of
astronomical sightings.
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