Bigfoot's screen test - analysis of the Patterson-Gilmin film of Bigfoot

Recent analyses propose that the 1967 film of "Bigfoot" documents a large, feral nonhuman primate unknown to modern science. Known sources of measurement error and existing data on human locomotion suggest a more cautious conclusion.

Of the varied sources of evidence invoked to support the existence of Bigfoot, none is more widely cited than the 1967 film of a large, hairy bipedal figure walking along the Bluff Creek drainage in northern California. Known as the Patterson-Gimlin film, this short motion picture (less than one minute running time) has generated considerable controversy with respect to its authenticity. The film depicts a burly figure walking deliberately away from the cameraman. The footage is often blurry due to excessive camera movement. In the most famous frame, the film subject turns its head and shoulders toward the camera to peer at its pursuer. Details of the subject's physiognomy cannot be discerned.

Recently, three independent studies have presented arguments suggesting that fabrication of the film would have been unlikely or impossible given the technology of the day. The implication, therefore, is that giant, bipedal primates have inhabited wilderness areas of the Pacific Northwest in recent times, yet have remained undiscovered by wildlife biologists and unrecognized among the mainstream scientific community.

In separate studies, Chris Murphy of Progressive Research(1) and Jeff Glickman of Photek and the North American Science Institute (NASI),(2) achieved a remarkable convergence of results when both investigators concluded, via different methods of estimation, that the film subject stood fully 7[feet]3 1/2[inches] (222 cm) tall. Glickman's study (1998) also concluded that the chest of the figure measured a hefty 83[inches] in circumference and that the film subject weighed in at 1,957 pounds.

In his book Big Footprints (1992), Grover Krantz makes two claims with respect to the film. First, Krantz argues that no human exists whose body dimensions match those of the film subject, even given the effects of a furry costume. Second, he claims that the kinematics of the film subject are decidedly nonhuman, that the gait could not be duplicated by a person wearing a costume.

In essence, two claims seriously undermine the hypothesis that the Patterson-Gimlin film is a hoax: (1) that the film subject's body dimensions are outside the range of human variation, and (2) that the gait of the film subject cannot be duplicated by a person.

In this report, we argue that the exact dimensions of the film subject are unknowable and that the gait of the film subject is easily reproducible by human beings of average stature. Neither of these arguments demonstrate that the subject of the film is not a Bigfoot; we simply wish to point out that recent trumpetings in cyberspace about the film's authenticity may not enjoy a solid empirical foundation.(3)

Analyzing the Claims

It is alleged that the film subject left tracks on the Bluff Creek sandbar, which were cast subsequent to filming. The tracks measured 14 1/2[inches] in length. About ten days after the film was made, Bigfoot investigator Bob Titmus reconstructed the subject's course of travel during filming and attempted to establish the position of Roger Patterson's camera during the event. These reconstructions were performed without a measuring tape or camera(4); quantitative efforts to map the positions of the cameraman and film the subject were made in subsequent years.(5) Thus, we know the general course of travel of the film subject but not its exact traverse (cf. Byrne 1975, Green 1981).

Murphy assesses the subject's height by taking a known quantity - subject heel width from footprint casts - and using this scalar as a calibration standard to determine film subject dimensions. Given the heel calibration and a "stoop factor" correction, he arrives at the stature of 7[feet]3 1/2[inches]. Murphy suggests that a stick recovered from the film site years after the event is also an appropriate calibration standard because the subject ostensibly is seen stepping over this stick during the film. Using this independent criterion, he obtains the same result.

In the NASI report, Glickman employs a third method that also yields the same height for the film subject. His method involves using a later photograph from the film site of an individual of known height, purportedly standing along the original path of the film subject, as a basis from which to determine the film subject's dimensions. This calibration photograph was taken by long-time Bigfoot investigator Peter Byrne five years after the film was made, and Glickman uses the alignment of dead trees that appear in the background of the film to match the photo with the relevant film frames.

Murphy and Glickman recognize that for a calibration standard to be valid, the object used for calibration must be coplanar with the film subject,(6) such that the calibration object and subject are equidistant from the optical axis of the camera. It is also well-established that, in order to minimize error, a calibration standard must be sufficiently large relative to the object being measured. Given the uncertainty of subject position in the film, it is not clear that objects chosen for calibration purposes lie completely within the intended reference plane. The dimension to be used in calibration and the subject of interest must be positioned equidistant to the camera lens to provide accurate measurement. Thus, a scalar dimension (a known quantity with which to scale other dimensions on an object or image) measured from a calibration standard that is not exactly coincident with a reference plane, even if that standard occupies a point in that plane, will yield uncorrectable errors if this obliquity is present (i.e., the standard is not aligned with the reference plane) but its degree is not known.