Description of Accelerometer Dataset

This Accelerometer dataset has 420 subjects and 51.67% of subjects are female. The median standardized BMI is 0.827 and 32.86% of subjects have asthma. This table further describes the covariates of this study.

The distribution of BMI based on sex is approximately normal.

The distribution of BMI based on a subject having a US-born mother is right-skewed, implying that children with an American-born mother are more likely to have higher BMIs.

There is great variability in median BMI among subjects when examining the interaction between sex and mothers country of origin. Males with a US-born mother have the highest median BMIs and females with a US-born mother have the lowest median BMIs.

Hypothesis Testing: Are Boys more active than Girls?

The hypothesis that boys are more active than girls is explored quantitatively, visually and statistically. The average total activity for female and male subjects is displayed below. The mean and median of total activity is noticebly higher for male subject, implying that boys are more active than girls.

The ridge distribution of male total activity is also higher than for female subjects.

A two-sample independent t test is performed to determine if the average total physical activity between the sexes is statistically different. At the 0.05 significance level, we reject that boys and girls are equally physically active. There is sufficient evidence that there is a significant difference in average physical activity between boys and girls. The 95% confidence interval implies that boys are more physically active than girls.

t.test(male_1$total_activity, female_1$total_activity, var.equal = TRUE, paired = FALSE) 
## 
##  Two Sample t-test
## 
## data:  male_1$total_activity and female_1$total_activity
## t = 3.6548, df = 418, p-value = 0.0002901
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  2720.022 9050.480
## sample estimates:
## mean of x mean of y 
##  65209.79  59324.54

How Does Season affect the relationship between Sex and Physical Activity

Season affects the relationship between sex and physical activity. During the summer, boys are margnially more physically active than girls (p-value = 0.049). During the winter, boys are significantly more physcially active than girls (p-value = 0.0006).

#Summer Physical Activity
t.test(male_2$total_activity, female_2$total_activity, var.equal = TRUE, paired = FALSE)
## 
##  Two Sample t-test
## 
## data:  male_2$total_activity and female_2$total_activity
## t = 1.9836, df = 150, p-value = 0.04913
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##    17.71549 9141.60556
## sample estimates:
## mean of x mean of y 
##  57897.75  53318.09
#Winter Physical Activity
t.test(male_3$total_activity, female_3$total_activity, var.equal = TRUE, paired = FALSE)
## 
##  Two Sample t-test
## 
## data:  male_3$total_activity and female_3$total_activity
## t = 3.4756, df = 266, p-value = 0.0005951
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##   3044.646 11002.236
## sample estimates:
## mean of x mean of y 
##  69585.50  62562.06

Observational Profile of Subjects over time

This figure displays physical activity of all subject over the 18 hour observational period (6:00am to 12:00am). There is a sharp drop off in activity during the middle of the day (nap time?).

Average physical activity based on sex

This plot displays average physical activity based on sex; we see that during most of the day boys are more physically active than girls.

Average physical activity based on season

Physical activity is varied by season. Subjects have higher physical activity levels during the winter. This is interesting because one would expect for children to be more active during warmer months when it is easier to particpate in non-sedentary activities (such as walking and playing at the park).

Average physical activity based on employment status of mother

Physical activity early in the morning is affected by the mother’s employment status. This suggests that children with working mothers begin to wake up and get ready earlier than children of non-working mothers.

Average physical activity based on television consumption

Additionally, physical activity is impacted by watching two or more hours a day of television. Subjects who did not watch television early in the morning had higher physical activity levels.