I’ve spent part of the last couple of days reading some of the arguments against the modern U.S. childhood vaccine schedule at places like the National Vaccine Information Center, SafeMinds, and in the medical investigative reporting of Robert F. Kennedy, Jr. One of the statements you run across quite often is that today’s children — going back to children born in early 1990’s — are less healthy and generally much sicker than children of earlier generations. Where does this idea come from? It turns out that one of the places that it comes from is a 2007 commentary published in the Journal of the American Medical Association (JAMA), entitled “The Increase of Childhood Chronic Conditions in the United States.” This commentary, by James Perrin, Sheila Bloom, and Steven Gortmaker — all of Harvard University — got an enormous amount of media attention, so it’s no wonder that it’s cited so often. Unfortunately, one of the most-cited statements from the commentary is an observations about time trends, in which the authors’ interpretations of the data are just downright wrong.
Bloomberg News Service started out their report on the JAMA commentary with the shocker, “The number of American children with chronic illnesses has quadrupled since the time when some of their parents were kids, portending more disability and higher health costs for a new generation of adults, a study estimates.” This is based on the following sentence from the JAMA commentary: “In 1960, only 1.8% of US children and adolescents were noted by their parents to have a limitation of activity due to a health condition of more than 3 months’ duration; in 2004, these rates had increased to more than 7% or more than 5 million children and youth.” This sentence is so loaded with problems that I need to devote a whole post to it, especially since it’s been quoted so often by the media.
If you’re a stickler for exactitude, you might be happy about two things, but not for long. Both the 1960 percentage of 1.8 and the 2004 percentage of 7 come from the same annual survey, The National Health Interview Survey (NHIS) carried out by the National Center for Health Statistics (NCHS). Both refer to the “percentage of children with limitation of activity resulting from one or more chronic health conditions.” Unfortunately, there have been several changes over time in the NHIS that render the two percentages incomparable, but the biggest problems are that:
(1) the definition of “children” in standard NHIS tabulations changed from 0-16 years old to 0-17 years old; and
(2) the NHIS question about activity limitation due to a chronic health condition changed completely between 1996 and 1997.
National Health Interview Survey Questionnaire Probes for Determining Presence of Activity Limitations, 1969-1996
Age under 1 year:
Is __ limited in any way because of his health?
Age 1-5 years:
Is __ able to take part at all in ordinary play with other children?
Is he limited in the kind of play he can do because of his health?
Is he limited in the amount of play because of his health?
Age 6-16 years:
In terms of health would __ be able to go to school?
Does (would) -_ have to go to a certain type of school because of
Is he (would he be) limited in school attendance because of his health?
Is he limited in the kind or amount of other activities because of his
All ages responding NO to the above probes:
Is __ limited in ANY WAY because of a disability or health? (Added in 1969)
[Note: At one point, the interviewer explains that the health condition or disability must have a duration of three months or more.]
(Source: National Health Interview Survey questionnaire 1980.)
National Health Interview Survey Questionnaire Probes for Determining Presence of Activity Limitations, 1997-present
Age Under 5 years: Parent is asked:
“Is (child’s name) limited in the kind or amount of play activities [he/she] can do because of a physical, mental, or emotional problem?”
[Note: At one point, the interviewer explains that the physical, mental, or emotional problem must be a condition that once acquired is not cured or has a duration of three months or more.]
Age 0-18 years, Parent is asked
(1) “Does (child’s name) receive Special Education Services or Early Intervention Services?”
(2) “Is (child’s name) limited in any activities because of physical, mental, or emotional problems?”
Age 3-17: Parent is also asked:
(3) “Because of a physical, mental, or emotional problem, does (child’s name) need the help of other persons with personal care needs, such as eating, bathing, dressing, or getting around inside the home?“
(4) “Because of a health problem does (child’s name) have difficulty walking without using any special equipment?”
(5) “Is (child’s name) limited in any way because of difficulty remembering or because of periods of confusion?”
(Source: National Health Interview Survey 2006.)*
As I noted above, the JAMA Commentary said: “In 1960…only 1.8% of US children and adolescents were noted by their parents to have a limitation of activity due to a health condition of more than 3 months’ duration…” The actual source for this percentage of 1.8 is an excellent 1984 paper by Paul Newacheck and colleagues in the American Journal of Publlic Health. For the subject of today’s post, the paper by Newacheck et al. is useful for two reasons: First, it has a table (Table 1) showing the year-by-year trend in per cent of children (under 17 years of age) with limitation of activity between 1960 and 1981. During that period the reported percentage increased from 1.8 to 3.8. Second, the authors examine in detail “the hypothesis that increased prevalence of activity limitations can be explained by changes in survey procedures, changes in awareness of illness, and/or changes in the size of the institutional population.” For example:
1. Prior to 1967, only those respondents who had reported a chronic condition in response to probes earlier in the interview were asked about the presence of an activity limitation.
2. Beginning in 1967, questions pertaining to activity limitation were asked of all sample persons.
3. Also beginning in 1967, activity limitation categories were read to the respondent; previously, respondents had been asked to choose an appropriate activity limitation response from a printed card.
4. Beginning in 1969, when persons responded negatively to the usual probes on activity imitation an additional question was asked: “Is __ limited in ANY WAY because of a disability or health?” It was then left to the coder to determine whether the response would be classified as an activity limitation.
Since the Newacheck et al paper is a public access article, I’ll leave it to you to read their thoughts on changes in the awareness of illness during 1960-1981 (”…increased awareness has not been a major contributor to the upward trend.”) and changes in the institutionalized population during the period. I do agree with Newacheck et al. that between the early 1960’s and the early 1980’s there probably was a near doubling of the proportion of children with limitations of activity due to chronic illness.
But what I’d really like to show you is more recent time trends, especially trends in the 1990’s and early part of this decade. Most of the the following data comes from the report, America’s Children: Key National Indicators of Well-Being, which has been published annually by the Federal Interagency Forum on Child and Family Statistics since 1997. For some years, America’s Children did not publish data for 0-4 year old children. For those years, I got the data from Health, United States, an annual report on trends in health statistics published by NCHS.
It seems that the standard NCHS definition of “children” for NHIS tabulations from 1960 through the 1980’s was “under 17 years of age.” I’m not sure why they chose 1984, but the Federal Interagency Forum on Child and Family Statistics seems to have asked NCHS to go back and do special tabulations for 1984, so they could use 1984 as their baseline or “benchmark” year.
TABLE 1. PERCENTAGE OF CHILDREN AGES 0-17 WITH ACTIVITY LIMITATION RESULTING FROM ONE OR MORE CHRONIC HEALTH CONDITIONS BY AGE, 1984
|Year||Total||Age 0-4||Age 5-17|
Table 2 shows prevalence rates from 1990 to 1996, when the NHIS question about limitation of activity due to chronic disease was the same as in 1984.
TABLE 2. PERCENTAGE OF CHILDREN AGES 0-17 WITH ACTIVITY LIMITATION RESULTING FROM ONE OR MORE CHRONIC HEALTH CONDITIONS BY AGE, 1990-1996
|Year||Total||Age 0-4||Age 5-17|
(Source: National Center for Health Statistics, National Health Interview Survey, 1990-1996.)
It looks like there was a jump in the prevalence rate between 1990 and 1991. Then the rates remained essentially stable between 1991 and 1996. Before you get all excited and conclude that “something happened” between 1990 and 1991 to “cause” these rates to increase, sit back and take ten deep breaths while I explain a few things. First, the entire increase occurred in 5 to 17 year-old children — not in infants and pre-schoolers. Second, these are not birth cohorts. The 5-17 year old children in the 1990 NHIS were born duing the period 1973-1985 and the 5-17 year old children in the 1991 NHIS were born in the perid 1974-1986. I hope you get the point.
Table 3 shows prevalence rates after 1996, when two things happened with the NHIS. First, as I mentioned above, the question on limitation of activity due to chronic illness changed enormously. Second, and equally important, between 1996 and 1997 a major NHIS Redesign occurred, which means that the sampling frame, sampling methodology, and many other statistical aspects of the survey changed. In short, both subject matter experts on childhood chronic disease and disability and statisticians agree that prevalence rates calculated from the NHIS in 1996 and before, and in 1997 and after, are not comparable.
TABLE 3. PERCENTAGE OF CHILDREN AGES 0-17 WITH ACTIVITY LIMITATION RESULTING FROM ONE OR MORE CHRONIC HEALTH CONDITIONS BY AGE, 1997-2006
|Year||Total||Age 0-4||Age 5-17|
|1998||No Data||No Data||No Data**|
(Source: National Center for Health Statistics, National Health Interview Survey, 1997-2006.)
My interpretation of this trend between 1997 and 2006 is that the overall prevalence rate is fairly stable. The same goes for the rate stratified by age: the prevalence for both infants and pre-schoolers and for 5-17 year olds seems pretty stable. I’ve provided tables with the actual prevalence rates, instead of a chart, so you can make your own charts, argue with me, and argue with each other to your heart’s content. (If you’re interested in statistical significance: For American’s Children NHIS staff did significance tests for difference between years for the period 1997 to 2005. No significance differences were found between years (p > 0.05). This means that differences between 1996 and ‘97, ‘97 and ‘98, etc. were all nonsignificant — adjacent years, in other words. As far as I know, no other significance tests have been done, e.g., for non-adjacent years or for trends.)
So my conclusions about the data on time trends in activity limitation due to chronic illness are: first, based on the 1984 paper by Newacheck et al. there was probably nearly a doubling of the prevalence rate between the early 1960’s and the early 1980’s. Second. based, on the data shown above, I think the prevalence rate has remained fairly stable between the mid-1980’s and 2006.
The ramifications of this are extremely important, especially regarding children of the 1990’s.
1. Children who were born and who grew up in the 1990’s aren’t any “sicker” than the previous generation, at least using this particular overall measure of chronic illness. The same thing seems to be true about children born during this decade — at least so far. I cannot disagree with the JAMA Commentary’s statement that chidhood asthma prevalence has doubled since the 1980’s. And there’s no doubt that childhood obesity has more than tripled since the early 1970’s. The JAMA commentary also points out:, “Approximately 6% of school-age children have a reported diagnosis of attention-deficit/hyperactivity disorder (ADHD), which represents a dramatic increase, although changes in diagnostic practices are clearly one reason. For example, there was no entry for ADHD in the American Psychiatric Association manual until 1968…Similar questions arise for autism spectrum disorders; whether or not there have been true changes in prevalence, it is clear that rates of diagnosis have increased.” (The JAMA commentary also cites a great review article entitled, “Is there an epidemic of child or adolescent depression?”, which I highly recommend. The simple answer is NO, there not an epidemic of child or adolescent depression.)
2. The focus of the National Health Interview Survey is obviously health, health care, and illness. The focus is not on neurodevelopmental disabilities such as ADHD, autism, and so forth, even though there definitely are questions that pertain to these health issues. I think that it’s extremely important that in this context, when parents are questioned about limitation of activity, NHIS data do not show a rising trend in line with the marked increase in autism and ADHD — or in the diagnoses of autism and ADHD.
Perhaps I’m making too much of this last point. After all, the reported prevalence of autism is still only 6.6 per 1,000, which is 0.66%. On the other hand, to estimate rates of parent-reported ADHD diagnosis, the CDC analyzed data from the 2003 National Survey of Children’s Health and reported that 7.8% (95% confidence interval 7.4-8.1) of U.S. children aged 4 to 17 years had had ADHD diagnosed at some point. However, according to some additional tabulations in Health, United States, 2007, of the 8.2% of 5 to 17 year old children whose parent reported them to have activity limitation resulting from a chronic health condition in 2004-2005 (see Table 3 above), in about 25% at least one of the chronic health conditions causing the activity limitation was reported to be ADHD. In other words, according to recent NHIS data the prevalence of ADHD that results in activity limitation is about 2% in 5-17 year olds. Contrast this with the overall ADHD prevalence from the CDC study just mentioned above.
Anyway, I stand by my major point above, that the kids growing up today — those born in the 1990’s and in this century — are not a “sickly” generation.
So I’ll leave you with the profound words of Pete Townshend, written in 1965 (and perhaps you can ponder how I wasted my wild, impetuous youth):
I don’t mind other guys dancing with my girl
That’s fine, I know them all pretty well
But I know sometimes I must get out in the light
Better leave her behind with the kids, they’re alright
The kids are alright!
*Note: I’ve shortened the series of questions to make them more readable. For the exact questions, skip patterns, etc., you can see the questionnaire at ftp://ftp.cdc.gov/pub/Health_Statistics/NCHS/Survey_Questionnaires/NHIS/2006/English/QFAMILY.pdf