nels (and sources) may also be in conflict. For example, messages about antismoking conveyed by a school-based intervention may disagree with tobacco company advertising.

Media Effects

Assuming that behavior change theory was used to identify the critical beliefs to target in a given population, to develop an appropriate message, and to select an appropriate source and channel, two additional questions must be addressed. First is the question of audience exposure. Will enough members of the target audience be exposed to the message, either directly or indirectly? Second, given sufficient exposure, how does the message influence beliefs (and behavior change)?

No matter how well designed a health communication message may be, it is unlikely to produce belief (or behavior) change if people are not exposed to the message. Considerations of exposure address two complementary issues: (1) What influences the likelihood that a person will be exposed to a given message? (2) How do effects vary with the degree of exposure achieved?

People cannot be exposed to a message if that message is not made available to them; perhaps the primary factor influencing whether or not a message will be available is funding. Money can buy media time and space, and unfortunately for the great majority of health communication intervention messages, little money is often available for purchasing media time/space or for paying outreach agents. Thus, the practical question for most health communication interventions is what gets a message free distribution. Free distribution may involve time or space in the mass media, whether in the form of public service announcements, health messages embedded in entertainment programs, or coverage of a health topic on news programs, in newspapers or magazines, or on talk shows. Free distribution outside the mass media may involve adoption of a message by community institutions. For example, youth organizations may offer to distribute antidrug messages to their members, or schools may add antidrug components to their after-school

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