Friday September 4 2015
Should parents try to limit their children's screen time?
"Just one hour of TV or internet use each night can damage a child's GCSE chances," says the Mail Online. Worrying headlines like this are being widely reported in the UK media based on the results of a 10-year-old study by researchers at the University of Cambridge.
The study looked for links between physical activity, sedentary behaviour and GCSE exam results. It found an extra hour of screen time every day was associated with a drop of two GCSE grades, while an extra hour of homework or reading led to improved academic performance. Physical activity didn't seem to have an effect on grades.
Although these findings may seem worrying, this study doesn't prove limiting screen time will automatically increase exam grades – but it does seem more time spent on homework and reading might.
A number of important factors aren't addressed by this study, such as whether the screen time included educational programmes or online revision. Research from 2005 also may not be as relevant now, with the wider availability of technology such as smartphones and tablets.
Where did the story come from?
The study was carried out by researchers from the University of Cambridge. Funding was provided by the Centre for Diet and Activity Research, the UKCRC Public Health Research Centre of Excellence, the British Heart Foundation, Cancer Research UK, the Economic and Social Research Council, the Medical Research Council, the National Institute for Health Research, and the Wellcome Trust.
It was published in the peer-reviewed International Journal of Behavioural Nutrition and Physical Activity.
This study has been widely reported, with a variety of UK media sources warning that spending more hours watching TV or using a computer could seriously harm GCSE results.
But most reports don't take into account additional study, the date of the research, or the type of screen time. A few sources, such as The Telegraph, point out the study doesn't prove cause and effect.
Although the news stories suggest replacing screen time with physical or social activities to boost results, this isn't one of the study's findings. Spending less time in front of a screen and more time on homework and reading was associated with improved grades, which is perhaps less surprising.
What kind of research was this?
This prospective cohort study aimed to investigate the association between physical activity, sedentary behaviour and GCSE results. This type of study can find associations, but it can't prove direct cause and effect.
The children were participants in the ROOTS study, which aimed to determine the relative contributions of genetic, physical, psychological and social variables to wellbeing and mental health during adolescence.
What did the research involve?
This study analysed data from the ROOTS study, which recruited children with an average age of 14.5 years from secondary schools in Cambridgeshire and Suffolk. With parent and student consent, their progress was followed through adolescence.
Physical activity data was collected six months after the study began. Trained researchers administered questionnaires, physical measurements and gave exercise instructions at participating schools.
Sedentary time and physical activity were also assessed using Actiheart heart rate and movement sensors and self-reported questionnaires. Participants wore the Actiheart for five days, including at the weekend, and reported the amount of time they spent awake or asleep.
Only participants who provided more than 48 hours of data were included in analyses. Physical activity and sedentary time was measured using a type of standard unit of activity called metabolic equivalent tasks (METs).
Self-reported sedentary time was recorded separately for weekdays and over the weekend for the following activities:
- watching TV (including video or DVD)
- using the internet
- playing video games
- doing homework (all classed as non-screen for analysis)
- reading for pleasure
Moods and feelings were measured for two weeks before the start of the study using the Moods and Feelings Questionnaire. Socioeconomic status was worked out using their home postcode and the Index of Multiple Deprivation.
GCSE results were obtained from the Department for Education National Pupil Database, and academic performance was calculated using a points system for grades.
The researchers looked for associations after adjusting for potential confounding factors, such as:
- body mass index (BMI)
- socioeconomic status
- the time of year the measurements were taken
- which schools they attended
What were the basic results?
The analysis was based on 845 adolescents with complete academic performance and activity data.
Girls were found to have significantly less internet and computer game time than boys, and spent more time reading and doing homework. Girls also performed better academically.
The study found an additional hour of daily screen time was associated with 9.3 fewer GCSE points, equivalent to the difference between two grades.
An extra hour of reading or homework (non-screen) was associated with 23.1 more points, reported to be the equivalent of one whole extra GCSE. The amount of physical activity taken wasn't associated with academic performance.
These findings weren't influenced by other variables. However, screen time was still associated with poorer scores after adjusting for physical activity, sedentary behaviour, reading and homework.
How did the researchers interpret the results?
The researchers concluded an extra hour a day of screen time at 14.5 years old is equivalent to around two fewer GCSE grades – for example, from a B grade to a D – at 16 years old.
It was suggested it may be important to find the right balance between screen time and time spent on other activities to improve academic performance. Encouraging more physical activity didn't seem to result in poorer academic performance.
This study assessed the associations between activity level, screen time, non-screen time and GCSE results in British adolescents.
The main finding was an extra hour of time spent watching television or on the computer was associated with lower grades at GCSE level.
An extra hour of reading or homework was associated with better performance. Screen time was still associated with poorer scores after adjusting for measured physical activity levels and reading or homework.
This study has taken a fair sample size from two regions in the UK. But about 15% of participants had incomplete data and weren't included in the analysis. We can't be sure whether their inclusion may have altered the results.
The researchers suggest those with missing data may have had better mood scores and were less deprived, which may limit how much their results might apply to all adolescents.
Some of the data, such as sleep and sedentary behaviour, was also self-reported. This means it's not possible to ensure the data was correct.
The researchers also acknowledge they weren't able to take into account that some screen time may have been for homework, revision or other educational purposes.
And as the study was carried out in 2005, the results may be less relevant to today's adolescents, who generally have wider access to screen-based technology.
Overall, this study is unable to prove screen time causes poor academic performance – but it has shown a possible link.
Parents and adolescents who are interested in achieving the best grades possible may benefit from spending more time on homework and reading instead of focusing on reducing screen time alone.