The author's conclusion doesn't involve the potential costs of advance screenings. She doesn't claim, for example, that the distributors' decision was based on an assessment of the cost of advance screenings compared to the cost of advertising. Rather, the author believes the film distributors' decision related to the potential for reduced interest in the film.

Necessary, because if the distributors didn't believe this, the author's conclusion wouldn't follow. If the distributors didn't think advance screenings could lead to a dampening of enthusiasm among people who would have otherwise been interested, then we'd have no reason to think the distributors' decision related to the potential for reduced interest.

The author's conclusion doesn't involve the enjoyment of potential audiences. She doesn't claim, for example, that the distributors' decision was based on concern that the audiences at advance screenings might not enjoy the film. Rather, the author believes the film distributors' decision related to the potential for reduced interest in the film. Whether audiences at the screenings would enjoy the film is a separate issue from whether the screenings could lead to reduced interest in the film.

A belief about the specific percentage that intends to see the film isn't necessary. Even if, for example, the distributors believed 95 percent of the public intends to see the film rather than 96 percent, that would not undermine the author's hypothesis that concern the screenings would reduce interest in the film explains the decision not to hold those screenings. The distributors could have believed screenings would reduce interest regardless of the specific percentage that would have been interested.

A belief about the specific percentage that would have viewed the film isn't necessary. Even if, for example, the distributors believed 50 percent of the public would see the film without advance screenings rather than 60 percent, that would not undermine the author's hypothesis that concern the screenings would reduce interest in the film explains the decision not to hold those screenings. The distributors could have believed screenings would reduce interest regardless of the specific percentage that would have viewed the films without the screenings.