Cause & Effect in Screen Time and Developmental Progress

Early childhood is a key developmental stage. As such, it is important to know and understand factors that promote (or harm) normal, healthy development. Although several studies have shown that higher screen time in children is related to poorer developmental outcomes, there is little evidence demonstrating the direction of that relationship. In other words, it is unclear whether: (a) screen time causes developmental delays, (b) developmental delays cause screen time, (c) some other external factor causes both developmental delays and screen time, or (d) all of the above. A recent study found evidence for a directional relationship between screen time and developmental delays. How did the authors come to this conclusion?

Longitudinal Studies

This was a longitudinal study, or a study conducted with the same participants over an extended period of time. This type of study is useful for establishing the direction of relationships between behaviours. It is especially useful in developmental research, as it allows researchers to observe how participants change (i.e., develop) over time.

Participants in this study were measured on three occasions: when their children were 2-, 3-, and 5-years old. Measurements included a developmental progress questionnaire and an estimate of screen time on a typical day, both reported by the mother.

Statistical Methods

By using a special statistical technique that can model the interactions between two variables at different times, the researchers could provide evidence for cause-and-effect relationships between developmental progress and screen time.

The results showed that there were statistically significant associations between higher screen time and lower scores on the developmental screening questionnaire later. As an example, higher screen time at age 2 was associated with lower developmental screening scores at age 3. There were no statistically significant associations between lower developmental screening scores and higher screen time later. This suggests that higher screen time causes slower development, not the other way around.


A Moment in Time

One limitation of this study, which applies to most research in the area of screen time, is that it only captures a moment in time. This study used data collected between October 2011 and October 2016, and with technology changing and improving so quickly, the findings may already be outdated as new devices and behaviours emerge.

Not All Screen Time is Created Equal

Another limitation was the treatment of screen time. The impact of screen time might depend on several factors including the type of media being viewed, whether the child is alone or with others. The design of this study does not account for this. The results therefore reflect the average relationship between screen time and development across all participants in their sample.

The authors acknowledged this limitation. They even demonstrated that both screen time and development varied based on several other variables, including whether the child was male or female, household income, physical activity, and hours spent sleeping per night. These variables changed the strength of the effect of screen time on developmental screening scores, suggesting that children are not equally affected by screen time.


What is the takeaway from this study? There is evidence to show that screen time has the potential to be harmful to child development. However, this is a complicated relationship that involves many factors, not just screen time by itself.

This study does not suggest that screen time is inherently bad. Instead, parents should be mindful of how their children are interacting with technology.

The BBC article that reported on the study points out that different national child research groups, including in the US, Canada, and the UK, have provided different guidelines for screen time among young children. This shows how research on the effects of screen time is still ongoing, but it can be confusing for parents who want straightforward advice. The Royal College of Paediatrics and Child Health in the UK does not suggest any hard limits on screen time based on age or hours per day, but it does offer some open-ended questions for families to consider:

  • Is screen time in your household controlled?
  • Does screen use interfere with what your family want to do?
  • Does screen use interfere with sleep?
  • Are you able to control snacking during screen time?

Questions like these will always be relevant, no matter the place or time.