CASE STUDY According to the Centers for Disease Control and Prevention (CDC), adults who engage in less than 30 minutes of moderate physical exercise per day should consume 1.5 to 2.0 cups of fruits per day and 2 to 3 cups of vegetables per day. Are adults meeting these recommendations? Not exactly, according to recent fruit and vegetable intake information obtained from the 2013 Behavioral Risk Factor Surveillance System (BRFSS).

The BRFSS is an ongoing, state-based, random-digit-dialed telephone survey of adults who are at least 18 years of age. It is the world’s largest ongoing telephone health survey system, tracking health conditions and risk behaviors in the United States since 1984. Data are gathered monthly from all 50 states, the District of Columbia (DC), Puerto Rico, the U.S. Virgin Islands, and Guam. In terms of gathering information about fruit and vegetable intake, survey respondents were asked to think about the previous month and to indicate how many times per day, week, or month they consumed whole fruit, 100% fruit juice, dried beans, dark green vegetables, orange vegetables, and other vegetables. Although close to 500,000 individuals were originally contacted to be a part of the survey in 2013, 118,193 respondents were excluded from analysis because they either resided in other countries, had missing responses to one or more questions, or had implausible reports of fruit and vegetable consumption (e.g., eating fruit more than 16 times per day or eating vegetables more than 23 times per day). The results reported in the 2013 BRFSS are based on the final sample of 373,580 adults.

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Across the states, results varied. The state with the largest number of survey respondents reporting meeting the daily fruit and vegetable intake recommendations was California. Of the 9,011 California residents who were surveyed, 17.7% met the daily fruit intake recommendations, and 13% met the daily vegetable intake recommendations. We know these numbers won’t be exactly right for the entire population of adults in California, but are they close?

In this chapter, we study confidence intervals. These are intervals that help us see how accurate numbers like 17.7% and 13% are. By the end of this chapter, you will be able to construct such intervals for proportions and means, and you will be able to interpret what such intervals represent.