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Correction
May 27, 2009

Incorrect Data in: Moderate-to-Vigorous Physical Activity From Ages 9 to 15 Years

JAMA. 2009;301(20):2095. doi:10.1001/jama.301.20.2095

Incorrect Data: In the Original Contribution entitled “Moderate-to-Vigorous Physical Activity From Ages 9 to 15 Years” published in the July 16, 2008, issue of JAMA (2008;300[3]:295-305), incorrect data appear. See also related letter in this issue.

On page 295, in the abstract, the second sentence of the Results section should be “Weekday MVPA decreased by 37 minutes per year, while weekend MVPA decreased by 39 minutes per year. By age 15 years, adolescents were only engaging in MVPA for 50 minutes per weekday and 36 minutes per weekend day. Boys were more active than girls, spending 18 and 14 more minutes per day in MVPA on the weekdays and weekends, respectively. The rate of decrease in MVPA was the same for boys and girls. The estimated age at which girls crossed below the recommended 60 minutes of MVPA per day was approximately 13.2 years for weekday activity compared with boys at 14.9 years, and for weekend activity, girls crossed below the recommended 60 minutes of MVPA at 12.7 years compared with boys at 13.6 years.”

On page 296, in Figure 1, under “Age 12 year assessment,” the number of adolescents who had valid accelerometer data and who were included in the primary analyses should be 695 and, under “Age 15 year assessment,” the comparable numbers should be 602.

On page 297, the fourth sentence of the first paragraph of “Monitored Physical Activity” should be “At 9 years, 95.4% of children who agreed to wear monitors had at least 4 valid days of data; the comparable numbers at ages 11, 12, and 15 years were 96.0%, 92.4%, and 86.6% (Figure 1).” The second sentence of the last paragraph in the middle column should be “Four-day reliabilities for minutes of MVPA averaged 0.75, 7-day reliabilities averaged 0.82, and 2-weekend day reliabilities averaged 0.56 across ages 9, 11, 12, and 15 years.”

On page 298, the last sentence of the first paragraph of “Activity Results” should be “By 15 years, adolescents were only engaging in MVPA for 50 minutes per weekday and 37 minutes per weekend day.” The last sentence of the second paragraph of “Activity Results” should be “At 9 and 11 years, almost all children met the guidelines, but by 15 years, only 32% and 18% met guidelines on weekdays and weekends, respectively.”

On pages 298 and 299, the first 3 paragraphs in “Results of Growth Curve Analyses” should be “Table 4 and Table 5 provide the significant findings for the growth curve models describing weekday and weekend activity. Both weekday and weekend MVPA showed significant linear decreases in MVPA between 9 and 15 years (model 1) of 37 and 39 minutes per year, respectively; however, the significant quadratic effect shows that the rate of decline leveled off as children entered adolescence. There was a high negative correlation (−0.95) between the weekday intercept and the linear slope at 9 years, indicating that children who were more active at 9 years tended to decrease activity more rapidly over time. At 9 years, children spent more time in MVPA on the weekdays than they did on the weekends (mean [SD] difference, 2.39 [21.76]; 95% confidence interval [CI], 1.05-3.73; t(1012) = 3.49; P < .001), but children who were more active during the week also tended to be more active on the weekend (r = 0.60).

Boys spent more time in MVPA at 9 years than girls did (190 vs 171 minutes per weekday, and 185 vs 171 minutes per weekend, respectively), but the linear decrease in MVPA on the weekdays and weekends was the same for both boys and girls (model 2). At age 9 years, boys were more active on weekdays than they were on the weekends (mean [SD] difference, 4.56 [22.56]; 95% CI, 2.59-6.53; t(506) = 4.55; P < .001), although girls were equally active during the week and on weekends (mean [SD] difference, 0.02 [19.56]; 95% CI, −1.69 to 1.73; t(505) = 0.03; P = .98). As shown in Figure 3, girls were below the recommended 60 minutes of MVPA on weekdays at approximately 13.2 years (95% CI, 13.0-13.4) compared with boys at 14.9 years (95% CI, 14.5-15.6); and for weekend activity, girls were below the recommended 60 minutes of MVPA at 12.7 years (95% CI, 12.5-12.9) compared with boys at 13.6 years (95% CI, 13.3-13.9).

As model 3 indicates, children from low-income families were more active at age 9 years on weekdays and weekends than were children from higher-income families (188 vs 178 minutes per weekday and 183 vs 175 minutes per weekend day). Income status was unrelated to changes in weekday or weekend activity. Both children from low-income and higher-income families spent more time in MVPA at age 9 years on weekdays than on weekends (low-income families: mean [SD] difference, 3.93 [22.74]; 95% CI, 0.96-6.90; t(227) = 2.61; P = .01; and higher-income families: mean [SD] difference, 2.58 [20.63]; 95% CI, 1.04-4.11; t(697) = 3.30; P = .001).”

On pages 300-302, the sixth and seventh paragraphs in “Results of Growth Curve Analyses” should be “For weekend activity, sex and BMI percentile had similar effect sizes (0.10 and 0.09, respectively), although the effect size for children from low-income families was somewhat smaller (0.07). Boys spent 18 more minutes per weekend day in MVPA than girls did; children from low-income families spent 10 more minutes per weekend day in MVPA than children from higher-income families did; and a 10% increase from the approximate mean BMI percentile of 65 was associated with 3 fewer minutes of MVPA per weekend day for 9-year-old children.

Children from low-income families had faster linear decreases in MVPA on both weekdays and weekends. Children with lower BMI percentiles had faster linear decreases in MVPA on the weekends. Also, the weekday MVPA of children living in the Midwest and South decreased at faster rates than children living in the West and Northeast. In general, these effects, although significant, were quite small. For example, the decrease in MVPA time each year for children in low-income families was approximately 1 minute more per day on weekdays and 4 minutes more per day on the weekends compared with children from higher-income families. Similarly, a 10% decrease from the approximate mean BMI percentile of 65 was associated with an additional less than 1 minute per day per year decrease in MVPA on weekends. Regional differences accounted for an additional decrease in weekday MVPA of less than 4 minutes per day per year.”

On page 302, the second sentence in the first paragraph of the Comment section should be “At 9 years, almost all children were well above the recommended 60 minutes of MVPA on both weekdays and weekends, but by 15 years only 32% met the guidelines on weekdays and only 18% on weekends.”

On page 303, the second sentence in the last paragraph of the first column should be “Another strength derives from our use of objective accelerometer measurement of physical activity in a much larger sample with a higher mean adherence rate for wearing the monitor over 7 days (52%) than the recent NHANES study (26%).22

The corrected Table 1, Table 2, Table 3, Table 4, and Table 5, and Figure 2 and Figure 3 appear herein.

Figure 2. Total Weekday and Weekend Day MVPA Distributions by Age
Figure 2. Total Weekday and Weekend Day MVPA Distributions by Age

MVPA indicates moderate-to-vigorous physical activity. Dotted vertical line indicates the recommended 60 minutes per day of MVPA for children.10 One child at age 12 years was missing weekday data and was only included in the weekend day analysis.

Figure 3. Average Weekday and Weekend Minutes of MVPA by Sex
Figure 3. Average Weekday and Weekend Minutes of MVPA by Sex

MVPA indicates moderate-to-vigorous physical activity. Dotted horizontal line indicates the recommended 60 minutes per day of MVPA for children.10 Graphs were generated from estimates obtained from growth curve model 2, which included intercepts, age, sex, age × sex, and age × age to describe change in MVPA on weekdays and weekends between ages 9 and 15 years. Girls cross below the recommended 60 minutes of MVPA per day at approximately 13.2 years (95% CI, 13.0-13.4) for weekday activity and 12.7 years (95% CI, 12.5-12.9) for weekend activity; boys cross below the recommended 60 minutes of MVPA per day at approximately 14.9 years (95% CI, 14.5-15.6) for weekday activity and 13.6 years (95% CI, 13.3-13.9) for weekend activity.

Table 1. Descriptive Characteristics of the NICHD Study of Early Child Care and Youth Development Cohort
Table 1. Descriptive Characteristics of the NICHD Study of Early Child Care and Youth Development Cohort
Table 1. Descriptive Characteristics of the NICHD Study of Early Child Care and Youth Development Cohort
Table 2. Mean Minutes of Moderate-to-Vigorous Physical Activity per Day
Table 2. Mean Minutes of Moderate-to-Vigorous Physical Activity per Day
Table 2. Mean Minutes of Moderate-to-Vigorous Physical Activity per Day
Table 3. Percentage of Children's Weekday and Weekend Day Activity by Age and Minutes of MVPA
Table 3. Percentage of Children's Weekday and Weekend Day Activity by Age and Minutes of MVPA
Table 3. Percentage of Children's Weekday and Weekend Day Activity by Age and Minutes of MVPA
Table 4. Weekday and Weekend Growth Curve Models Examining the Change in Moderate-to-Vigorous Physical Activity Between Ages 9 and 15 Years (Models 1-3)a
Table 4. Weekday and Weekend Growth Curve Models Examining the Change in Moderate-to-Vigorous Physical Activity Between Ages 9 and 15 Years (Models 1-3)a
Table 4. Weekday and Weekend Growth Curve Models Examining the Change in Moderate-to-Vigorous Physical Activity Between Ages 9 and 15 Years (Models 1-3)a
Table 5. Weekday and Weekend Growth Curve Models Examining the Change in Moderate-to-Vigorous Physical Activity Between Ages 9 and 15 Years (Model 4)a
Table 5. Weekday and Weekend Growth Curve Models Examining the Change in Moderate-to-Vigorous Physical Activity Between Ages 9 and 15 Years (Model 4)a
Table 5. Weekday and Weekend Growth Curve Models Examining the Change in Moderate-to-Vigorous Physical Activity Between Ages 9 and 15 Years (Model 4)a
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