CANPLAY effectively demonstrates that pedometry methods are feasible for obtaining large scale national prevalence data of physical activity levels in children and youth. In fact, CANPLAY is currently the largest database of pedometer data collected in any single sample to date . Similar to findings from other pedometer-based studies , Canadian girls take consistently fewer steps/day than their male counterparts. Although, as depicted in Figure 2, steps/day followed a similar overall decreasing pattern with age as that based on smaller and typically school-based samples , comparatively, Canadian boys and girls generally took fewer steps/day. In addition, the assembled values  portray a distinct increase in pedometer-determined physical activity in childhood (with boys increasing even more than girls), that subsequently declines in youth. In contrast, the CANPLAY data display no notable rise in steps/day in childhood past age 6, but instead depict a slow and steady decline in values through childhood and into youth.
On average, CANPLAY parents reported that Canadian boys and girls watched < 40 minutes of television between school and dinner on a typical school day. Although not directly comparable in terms of the exact time frame queried, ≅36% U.S. youth (aged 14-18 years) in the Youth Risk Behaviour Factor Survey (YRBFS) reported watching ≤ 1 hour television on school days  when queried directly. Similarly, ≅39% of U.S. children and youth aged 8-16 years reported that they watched ≤ 1 hour of television on the day prior to their interview conducted as part of the National Health and Nutrition Examination Survey (NHANES); 26% reported watching ≥ 4 hours . We are unable to do more direct comparisons with these examples of American data because of the difference in the time period examined, and the manner in which the question was queried (parent proxy). In addition, the 95th percentile of the distribution of the CANPLAY data was 2 hours and the 99th percentile was 4 hours. It is difficult to say to what degree these discrepancies merely reflect methodological differences or may represent some true country differences in young people's behaviours.
Television watching is only one of many frequently occurring sedentary behaviours in which young people may engage during leisure time. Others include a range of electronic media use such as computer use, video games, social networking, etc. However, television watching has a stronger relationship with pedometer-determined physical activity than video gaming, and consideration of both simultaneously does not necessarily strengthen the relationship in children . Almost half of daily pedometer-determined steps are attributable to after-school activities . If these are pre-empted in favour of television viewing, then an important opportunity to be active is logically lost. Specifically, since time is finite, each hour spent watching television represents a missed opportunity to accumulate up to approximately 6000 steps or more . In addition to replacing opportunities for active alternative behaviours, exposure to television might also impact body weight by promoting excess energy intake. Specifically, evidence indicates that children's television viewing and snacking behaviours are related , more television viewing is associated with adverse dietary practices , and children consume more available snacks when exposed to food advertising . These additional factors make television viewing potentially more insidious a risk factor for childhood obesity than other forms of sedentary behaviour that are less associated with energy intake.
The odds of being obese were 64% lower for a child in the highest quintile of pedometer-determined physical activity on weekdays (i.e., taking 15075 or more steps/day) than a child in the lowest quintile (i.e., 8664 or fewer steps/day). In contrast, the adjusted odds were 42% higher for a child in the highest quintile of television watching (60 minutes) than another child in the lowest quintile (watching no television between school and dinner). Watching television between school and dinner increases the likelihood of being overweight or obese, and taking more steps/day reduces the likelihood of obesity (but not overweight). Considered together, a child taking ≅15,000 steps/day on weekdays and watching 2 hours of television between school and dinner has a 51% lower likelihood of being overweight/obese and has a 83% lower likelihood of being obese compared to a child taking ≅8780 steps/day and watching no television between school and dinner on a typical school day.
In contrast to the obvious findings related to obesity, a clear association with pedometer-determined physical activity was not apparent with overweight. Although the observed decrease in steps/day and increase in television watching behaviour with increasing BMI-defined obesity categories follows expected changes for the most part, the discrepancy in daily steps is greatest in the transition between the overweight and the obese categories. Stated another way, the overweight children are more like the healthy weight children in their step-defined physical activity behaviours, but differ in their television viewing behaviours. As these are cross-sectional data, we are unable to conclude causal relationships in terms of whether such behaviours caused the overt obesity, or, alternatively, whether they may only reflect current behavioural choices of overweight and obese children in Canada.
A number of limitations must be acknowledged. We only asked the education of the responding parent and relied on parent-reported estimates of children's height and weight. We also only queried about television watching between school and dinner; the effects of television watching at other times was not examined. Pedometers do not detect all types of physical activity, for example swimming, a popular activity among Canadian youth (44%) . However, CANPLAY participants were instructed to remove the pedometer (for example, when swimming) and to record all reasons for removing it during the course of the day. Less than 0.5% reported removing it for swimming during the 7 day period . And although pedometers lack the ability to distinguish time spent in sedentary and low-, moderate- and vigorous-intensity activities, they nonetheless provide valuable information on the total level of physical activity relevant to policy. For example, we found that obesity was inversely associated with pedometer-determined steps/day.
Although it remains plausible that certain individuals may alter their behaviour in response to being knowingly monitored, as previously documented, there was no detectable evidence of reactivity on a population basis in CANPLAY . Furthermore, although additional days provided improved reliability and validity, the first day alone was a reasonable representation of mean steps/day over a 7 day period in terms of reliability (ICC = 0.79) and validity (relative absolute percent error = 2.5%) . Moreover, it is reasonable to presume that the cost of pedometer monitoring is less than that required to conduct accelerometer-based surveillance of a sample of the same size. The CANPLAY pedometers were purchased for $20 CAD each, mailed out and also returned by mail, and data management focused on 7 steps/day entries recorded on a log. In contrast, the NHANES used an accelerometer  that cost $335 USD and required initialization, primary distribution was conducted in a face-to-face manner but then return was by mail, and data management required technical expertise and time to download and manipulate manifold amounts of raw data to obtain desired outputs. Finally, we used a 3000 step conversion for 30 minutes of moderate-to-vigorous intensity activity based on adult studies [19, 20]. A single study  with 10-12 year old children suggests that 3600 steps might be more precise, at least in this age group. Post hoc we re-ran the analysis using the 3600 step conversion and found minor (1-2%) decreases in odd ratios for the association between overweight and obesity and pedometer-determined steps/day, but no changes in significance of any of these findings. We decided to stay with presenting the results using the 3000 step conversion as it is a more conservative estimate of the number of steps that a broad age range of children might accumulate by replacing 30 minutes of television watching with activity of various intensities.
Telephone recruitment in CANPLAY permitted the sample design to be less complex than would be required for clustered school-based samples. While this permitted broader coverage, extending to less populated areas, it may have contributed to a higher rate of loss of pedometers (30%) relative to what might be expected in a more controlled environment such as school-based collection (although we know of no comparable published data documenting instrument loss specifically). As we have previously published , about 60% of CANPLAY participants returned pedometer data (10% returned pedometers without logged steps) and over 95% of those wore the pedometer for at least 5 days. Participation was lower among 15-19 year olds, those whose parents had less than secondary education, and higher among children age 5-10 years and those whose parents reported a university education .