In terms of return on investment, family fare is 78 per cent more rewarding than blood and guts. Coming shortly after Walt Disney announced plans to re-focus its efforts on family films, the report may strike a chord among studios that are struggling to find a formula for consistent box office success.

Dove, using data commissioned from Paul Kagan Associates, a respected research firm, claims its findings "completely debunk" film-makers' claims that films stuffed with "naked bodies, exploding heads and filthy language" make most money.

Although the findings on profitability are based on estimates of numbers studios never reveal, but are commonly used as rule-of-thumb measures of success, the results seem to suggest scarcity value is a financial factor.

Of the 2,380 films given a wide US release (on 800 or more screens) in the decade to the end of 1997, only 75 were given a G rating. Walt Disney's main label, Buena Vista, provided 23 of those, with Warner Bros a distant second with 13.

Sony, which came close to collapse in the period under scrutiny, was the most prolific studio, with a total of 271 releases; it put out the most R-rated pictures (137) and made only four with the G rating. Since 1968, Dove says, 60 per cent of all releases have been rated R.

Dick Rolfe, the foundation's chief executive, has sent copies of the report to studio executives and mutual fund and pension fund managers, in an effort to persuade both groups to review their policies "for profit's sake".

Average gross profit from a G-rated film in the review period was $94m, the study says, with R movies yielding only $11m apiece and PG products about $26m. Gross profit is defined as the studios' estimated revenues from cinemas, home video, and television rights minus production and promotion costs.

According to the data, G and PG films enjoyed a come-back between 1993 and 1996, as the number of R-rated releases fell to a low of 99 in 1994, but the tide turned quickly, and the tally of films unsuitable for family audiences hit a record 169 in 1997.

The change in the mix reflects the studios' pursuit of young males, the most persistent cinema-goers, and their response to the early adoption of adult tastes by children which has lately afflicted toy industry sales. Effects-heavy action films, commonly rated PG-13 or PG, are widely accepted in the marketplace as family viewing.

The Dove Foundation, supported by entertainment names such as Steve Allen and Michael Medved, securities executives and the former head coach of the Dallas Cowboys, acknowledges this shift with a less rigid stance than some advocacy groups.

It has given its "family approved" seal to several serious, R-rated films, including Steven Spielberg's Schindler's List and Saving Private Ryan. "Moviegoers are not crying out for endless sequels of Rugrats and Babe," says Mr Rolfe, who rates the newly-released Star Trek: Insurrection (PG) as acceptable family viewing.