Cell Phones and Behavior

Cell phones continue to be a focus of epidemiological studies and public concern, despite the fact that so far there is no compelling evidence of any health risk from cell phones. Concerns are likely to be sparked anew with the report of a study linking cell phone use to behavioral problems in children.

The study, by Divan, Kheifets, Obel, and Olsen, is a follow up of a prior study which showed a correlation between cell phone use in pregnant women and behavior problems in their children. They sought to replicate this study with a larger data set and taking into consideration more possible confounding factors. They found:

Results The highest OR for behavioural problems were for children who had both prenatal and postnatal exposure to cell phones compared with children not exposed during either time period. The adjusted effect estimate was 1.5 (95% CI 1.4 to 1.7).

Conclusions The findings of the previous publication were replicated in this separate group of participants demonstrating that cell phone use was associated with behavioural problems at age 7 years in children, and this association was not limited to early users of the technology. Although weaker in the new dataset, even with further control for an extended set of potential confounders, the associations remained.

For children of mothers who used cell phones, and who also used cell phones themselves, there was a 50% relative increase in reported behavioral problems. For children who did not use cell phones but whose mothers did while pregnant, the relative increase was 40% – these relative increases are with an absolute baseline risk of 2% reporting behavioral problems (so a 50% relative increase would be a 1% absolute increase in risk). This is a small, if statistically significant, effect. An odds ratio of 1.5 is a reasonable effect size, depending on what is being measured. In this case the outcomes were based upon questionnaires, and are therefore reliant on subjective reporting.

The results of this study are interesting, but the usual caveats apply. The absolute effect size is small, and the outcomes based upon subjective reporting. This is an observational study, not an experimental study, so no conclusions can be drawn regarding cause and effect. The study authors did not even speculate about a possible mechanism, and would not suggest that cell phone use causes the observed behavior problems.

It should also be noted that while this study replicated a previous study, the effect size was smaller. Also, accounting for other possible correlates, such as social status and maternal history of behavioral problems, tended to decrease the effect size as well (although not eliminate it).

It is possible that the correlation is spurious or is an artifact of reporting bias. If the correlation is real, it seems likely that there are confounding factors that have not been sufficiently accounted for. The authors themselves considered as many as possible. They report:

“One thought was that it was it not cellphone use but mothers’ inattention that led to behavior problems. While it was important, it didn’t explain the association that we found.”

So inattention partially explained the results – perhaps other behavioral or personality attributes also correlate with both cell phone use and behavior problems. Given that the absolute effect size is small (about 1%) there can be many such factors that can exert such an effect, and it is unlikely that the authors thought of all of them.

The plausibility of a direct effect of cell phone use is quite low. Physicists have pointed out that cell phones generate only small amounts of energy, the primary effect of which is to heat up surrounding tissue. But the non-ionizing radiation from cell phones, by definition, is of too low energy to break chemical bonds or cause any cellular damage. Concerns over cell phone use have largely surrounded the risk of brain cancer, and epidemiological studies have not shown increase in brain cancer overall or an increased risk correlating with cell phone use. The data does not entirely clear cell phones either, but so far the evidence does not support a link.

Given the low biological plausibility and generally negative epidemiological data, it is unlikely that cell phones directly cause any biological harm. This also applies to behavioral problems, as investigated in this study.


While sure to garner headlines, this study is not compelling evidence that cell phones are a health concern with regard to behavioral problems in children. The study found a small absolute effect size which is very likely to be due to confounding factors that were insufficiently accounted for in this study. It is very difficult to derive any firm conclusions from observational studies such as this. Many such studies are required to pinpoint a likely cause and effect relationship – no one observational study can do this.

I do not even think that this study warrants precautionary measures, as the likelihood of a real risk from cell phones is small and implausible. Cell phone use is increasingly common, and epidemiological studies such as this are certain to turn up a great deal of noise in the data – apparent correlations or the downstream effects of complex behavioral influences. There are likely to be more studies showing similar apparent correlations and it would be premature to respond to each one with calls for precautionary measures.

At best this study suggests questions for future research. But the results are within the predictable noise of preliminary epidemiological data that is best ignored by the public. Most such correlations do not hold up with future research and the ultimate interpretation of such correlations is often different from the most direct cause and effect that grabs headlines and public attention. Basing decisions on preliminary epidemiological evidence such as this is likely to be unnecessarily disruptive and inconvenient and is unlikely to provide any health benefit.

Posted in: Public Health

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10 thoughts on “Cell Phones and Behavior

  1. Reductionist Nurse says:

    Any novel activity or technology adopted by the next generation will ultimately become the scapegoat for its predicted downfall. My grandmother showed me a book titled “From the Ballroom to Hell.”

    Whether its ballroom dancing, book reading, rock and roll, movies, video games, or cellphones, something inevitably must draw the flames of the elders and sociologist, lest we waste our time on more fruitful ventures. My first reaction to children with phones is jealousy, because that would have been awesome when I was their age, lucky punks.

  2. Ken Hamer says:

    Given the number of particularly obnoxious cell phone users, as observed in airplanes, while driving, or in restaurants and cinemas, I think the effect is more likely a “learned” behaviour.

  3. “I do not even think that this study warrants precautionary measures, as the likelihood of a real risk from cell phones is small and implausible.”

    Well, we know that cell phones are linked to road accidents and bad driving. We don’t conclude that BECAUSE – A it’s implausible that the linkage is due to non-ionizing radiation THEN B – cell phone use while driving is just peachy.

    People who work with families just hate watching parents gossiping on their cell phones and swatting away their children and telling them to shut up.

    I remember reading about a study many years ago in the days of black rotary phones. An attempt was made to link charateristics of households to stress. (Working parents, kids in school, size of house etc.) Unexpectedly, the biggest correlation was with the number of telephones in the house. Houses with five telephones were more stressed than those with just one. The association was believed to be real, though not due to EMR.

  4. windriven says:

    For those interested, the initial study was conducted with N=13,000. The study Dr. Novella reports on today included 28,745 children. I was unwilling to pay $30 for the whole enchilada but it would be interesting to see how carefully the authors tried to identify potential confounding factors.

    I’d also like to know the number of controls and under which rock the authors found several thousand mothers who haven’t used cell phones during the past 7 years. I’ve spent a bit of time in Denmark and can’t recall ever knowing a Dane who eschewed cell phones. We aren’t comparing ethnic Danish cell phone users with recent Somali immigrants are we?

  5. ConspicuousCarl says:

    The free abstract is too vague to get any information.

    Were these cases really each rated as the child either having or not having behavior problems?

    Each child should have a rating for how bad the behavior actually is, even if it is self-reported. No matter how certain it is that the typical child in Group B will be X% worse than Group A, I want to know how that rate compares to the variation within a group.

    Was it a black-and-white matter of turning 98 angels and 2 devils into 97 angels and 3 devils, or were many of the kids different degrees of proximity to some behavior threshold and the phone exposure (or other factor) just barely pushed one over? If it is the second case, the information is basically worthless to any individual even if the hypothesis is true.

    And that all is a problem even if we assume that confounding factors are not present. Since this is essentially a voluntary response survey (not the self-reporting of problems, but the parents having already chosen to either use or not use phones for unknown reasons), it is hard to take seriously.

  6. ConspicuousCarl says:

    windrivenon 08 Dec 2010 at 6:06 pm
    [...] under which rock the authors found several thousand mothers who haven’t used cell phones during the past 7 years.

    Yeah, that’s a good one, and it makes confounding factors even more likely to be an influence.

    When the group division is based on some seemingly irrelevant detail (like whether one chooses to buy bleached flour from Wonder Bread or Mrs. Baird’s), maybe the choice was functionally random.

    But when being in one group is just downright weird, it greatly increases the probability that the decision was made based on some mentality which affects all of their behavior.

  7. desta says:

    “From the Ballroom to Hell.”

    @ reductionist nurse: fantastic title.

    Hmmm……, moms who spend more time on the phone have naughtier children?
    Maybe those kids are naughty first (even in utero: quit kicking!) and hence moms then feel the need to call everyone they know to vent.
    Maybe people who talk on their cells all day tend to be more annoying, and so their kids tend to be more annoying, because they inherit the annoying gene (which apparently used to be expressed via ballroom dancing).
    And subjective reporting? Okay. So the minute I answer my phone is the minute my kids want to talk, chant and scream (confirmation bias? probably).

  8. desiree says:

    no need to worry, you can buy a radiation-shielding belly band!

    i’m curious, did the study authors check for a dose-response relationship? did they find one? if cell phones really were a problem, wouldn’t sticking one in your pocket while pregnant be worse than talking on one?

    thanks for your analysis dr. novella, i’d seen the headlines and doubted that the study warranted the attention it got, but you never know.

  9. Charon says:

    Physicists have pointed out that cell phones generate only small amounts of energy, the primary effect of which is to heat up surrounding tissue.

    Thanks for noting this, but even this statement is too strong. While the microwaves dump some tiny amount of energy into the surrounding tissue as heat, it has a negligible effect on the temperature of the tissue. Even if the phones dumped their entire energy output into the tissue (which, obviously, they don’t), this is ~1 foot off the side of a 60-watt incandescent bulb. Blood efficiently moves that heat elsewhere in the body. Plus, your body is pretty good at getting rid of excess heat.

    So if using a cell phone is bad, exercising must be horrible ;)

  10. Charon says:

    Why, oh why, can’t we edit our comments… somehow “this is the equivalent of holding your hand >~1 foot off the side…” became “this is ~1 foot off the side”. WTF?

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