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Ask the Expert: Dr. Kirsten Herrick
August 14, 2014
The NHANES National Youth Fitness Survey (NNYFS) was developed as a model of comprehensive, youth-targeted fitness and nutrition data collection. As a standalone survey conducted alongside the National Health and Nutrition Examination Survey (NHANES), NNYFS collected data on exercise and nutrition habits of U.S. children aged 3 to 15, through interviews and fitness tests conducted in a dedicated mobile examination center trailer. Selected data from the 2012 NNYFS and NHANES surveys were recently released in Data Brief 157, "TV Watching and Computer Use in U.S. Youth Aged 12–15, 2012." We spoke with Dr. Kirsten Herrick, senior research fellow and the Data Brief's lead author, about the findings.
Q: Tell us about excessive screen-time behavior.
A: Well, excessive screen-time behavior is anytime you're sitting in front of a screen for longer periods than are recommended.
Q: Two hours or less a day, those are the American Academy of Pediatrics guidelines.
A: Yes. So that screen-time could be replacing more active pursuits. It's a time period when lots can happen, the opportunity to be barraged with all sorts of negative media from all sorts of different sources—violence, high-calorie, low-nutrient value foods. What's interesting from this Data Brief is, although the numbers weren't surprising—lots of kids have access to TV and computersa reminder to parents to really think about how much time their kids are getting in front of TVs or computers, because it's so easy to forget about it.
Q: You weren't surprised at these high numbers?
A: No (laughs). I don't know that there are many American households that don't have a TV. And certainly now, with the advent of personal [smart]phones, you can stream television and internet and all sorts of things. So it's not surprising.
Q: This is all self-reporting for 12 to 15 year-olds.
A: Correct. For younger children, 3 to 11, we actually have a proxy respond for them. This [12–15] is kind of a funny age group, because they're not out on their own, no driver's license, but they are pretty independent, they're doing a lot on their own. But it's still important for parents to be involved. Studies have shown that families who spend time eating together and exercising together have better health outcomes. And we know that all those practices in our early life tend to play out in our later life. So it's all about life course setting for good outcomes in later life.
Q: You mention smartphones. This Data Brief reports on TV watching and computer use. Were there any data here about everybody watching their iPhones and Android phones?
A: We don't know exactly how participants would have qualified those types of devices. It's possible that a child might say, "Oh yeah, I was watching a show on my iPhone or dad's iPhone, and that was part of my screen time." However, they could have also put it in a separate box and said, "Well, you didn't ask me about smartphones." There needs to be more research in this area. The technology is changing so fast that it's really hard to capture what's important. That's also borne out when we talk about, is it the amount of time you sit watching TV, or what you're being exposed to? Because there may be some screen-time activities that are good.
There are all sorts of educational programs, maybe if they're spending time doing that, it's a good thing. Or if they're sitting with their families watching a movie or doing other family-time activities, like more active video games, maybe those are good things. We know that, in general, a lot of screen time is bad, but what exactly about screen time is problematic?
Q: Does the NHANES that's currently in the field attempt to break down the technologies that would qualify as TV?
A: We haven't made any changes to these questions yet. There is talk of how best to measure them, but I don't think there's any consensus yet on the best way to capture this information.
Q: The NHANES National Youth Fitness Survey was in the field for just 1 year?
A: Yes, NHANES National Youth Fitness Survey was in the field just in 2012. And the data we analyzed is actually from the NHANES National Youth Fitness Survey, and the National Health and Nutrition Examination Survey [NHANES] 2012. NHANES also asks this [age group] panel questions, so we were able to use data from both sources. We only included the 2012 NHANES data, because of [data] merging, and sample weights, and things like that. But this section of questions is also asked in other years in NHANES, so there is some hope that we can look at trend data over the years. We just don't have enough data points to really call it a trend.
Q: This is the third Data Brief to come out of the NHANES National Youth Fitness Survey data. In Data Brief 141, we noted that about one in four of U.S. youth aged 12–15 years engaged in moderate to vigorous physical activity for at least 60 minutes a day, meeting the guidelines. And in your Data Brief 157, you say about one in four keep their screen time within guidelines. Could you draw a line between 25% meeting their screen time guidelines, and 25% meeting their physical activity guidelines?
A: (Laughs) It would be nice if you could draw that line, but we haven't done that analysis. Certainly, that's what a lot of the activity programs would like you to think, that if you're not sitting doing screen time, maybe you're replacing it with a more physically active activity. And, we certainly hope so. That's what the media campaigns argue for. But we don't know exactly what they're doing.
Q: How do you feel about the quality of the data that's come out of the survey, and would you like to see more reporting coming out of it in the future?
A: I definitely think more reporting out of this data in the future would be great. The NHANES National Youth Fitness Survey was a very unique opportunity to collect data on individuals who are very important to our future. We want to know that they're healthy and they're making good choices that will follow them throughout the rest of their life.
There will be a lot of future work on how best to capture things like screen time, but also physical activity. There is a lot of research going into that area because we had physical activity monitors, and they collect mountains of data. How do we best summarize that? And then, once we summarize it, what do we look for? How do we use that going forward, comparing that to maybe eating habits or looking at screen time. This is just the beginning, and NHANES is the perfect vehicle to take it forward, because of the rich data source that it provides. I hope that they'll have an opportunity to do this again, and as we continue to do it, maybe we'll be a little bit more refined in some of our questions, try and get a handle on screen time.