I have been an avid reader and admirer of The LA Times for 40 years. I write you now to give you a brief résumé of the movie industry's voluntary film rating system. The facts of its birth, design and collide with your Oct. 14 editorial

First, the Motion Picture Assn. of America withholds the names of the rating board members so they won't be harassed by disgruntled producers. Grand jury members' names are withheld; so are criminal jury members, all for the same reasons. There's nothing sinister about this. We convey to the press, upon request, a brief biography of each rater. We could make public their names, but if we did, how would that advance the quality of the ratings? We merely want to protect raters from the kind of harassment that was depicted in the Kirby Dick film "This Film Is Not Yet Rated." Their qualifications? They are parents, who see a film through the eyes of a parent. We have three senior raters who give historical knowledge to the system, have administrative duties and whose children, young when they started, are now over 17. The rest have younger children.

When I designed the rating system in 1968, I retained two social scientists from different universities. I asked them to put to paper the precise demarcations between rating categories so we would have specific guidelines. For example, what is too much violence for each of the categories? Much as the Supreme Court to this hour cannot define "pornography," these professors were unable to mark precisely where the lines should be drawn. Like Justice Potter Stewart's musing about pornography, the raters can say, "I can't define it but I know what it is when I see it."

The rating system will be 38 years old on Nov. 1. Is it fair to say that nothing lasts that long in this brutal marketplace unless it is providing some kind of benefit to the people it aims to serve -- in this case, parents. I suggest you might want to take your own poll of parents with young children who work for The Times. Every year since 1969, the Opinion Research Corporation of Princeton, N.J. conducts national polls annually under strict market research protocols with some 2,600 respondents. For the last 15 years, more than 70% of parents with children under 13 find the system to be "Very Useful" to "Fairly Useful" in helping them guide their children's movie going.

The 2006 poll, with 2,031 respondents was in the field when "This Film Is Not Yet Rated" was in exhibition. The results are just in: an increase in approval by parents with children under 13 to 80%. Those who said the rating system was "Very Useful" rose 10% higher than last year. This latest poll underscores my central theme that parents, for whom the system was designed, are highly approving of what it does -- they trust it.

The movie rating system is voluntary. No one is compelled to submit a film for rating. I know the counterargument: "If I don't submit for rating, my film will have trouble getting theater play dates." But that's a decision to be made by theater owners, not the rating system.

This letter is sent to you with admiration and respect.

Jack Valenti is the former president of the Motion Picture Assn. of America.