by James Lyons-Weiler, PhD, Popular Rationalism, ©2025
(Apr. 18, 2025) — The 2002 New England Journal of Medicine article by Madsen et al., often cited as pivotal in “debunking” the link between MMR vaccination and autism, contains numerous red flags that point to serious flaws and, potentially, elements of scientific misconduct or fraud. A thorough forensic analysis reveals multiple issues involving inappropriate handling of confounders, diagnostic biases, misrepresented incidence rates, and modeling weaknesses. Here’s a critique of the study, line by line and layer by layer:
Inaccurate and Obsolete Autism Rates
The authors reported 7.7 per 10,000 for autistic disorder and 22.2 per 10,000 for other autism spectrum disorders in 8-year-old children. But by 2002, multiple studies had already documented rates several times higher. Even CDC data showed rising prevalence by the late 1990s. For example:
- The California DDS (1999) report cited in the study noted a 373% increase in autism caseloads between 1987–1998.
- The authors mention in passing that Danish rates rose to >10 per 10,000 in 2000 but then claim their lower prevalence is valid and comparable.
Conclusion: They used outdated diagnostic tracking systems, which likely underreported true autism prevalence, especially among the unvaccinated group that was younger and less likely to be diagnosed. This creates an artificial suppression of autism incidence in the unvaccinated group, potentially reversing the actual signal.
Model Overfitting via Confounder Overadjustment
In their multivariable Poisson regression model, the authors included seven covariates:
- Age (as a time-dependent variable),
- Calendar year,
- Sex,
- Birth weight (5 levels),
- Gestational age (3 levels),
- Mother’s education (5 levels),
- Socioeconomic status (6 levels).
Many of these are collinear or surrogates for one another (e.g., mother’s education vs. socioeconomic status; gestational age vs. birth weight), inflating the risk of overfitting the model. Additionally, age was the dominant confounder since diagnosis rates depend heavily on age. But they treated age and calendar year and birth cohort and diagnostic delay—intertwined temporal factors—as independent, diluting statistical power.
Conclusion: This is classic overadjustment bias, where true effects may be nullified by excessive modeling of correlated variables. The low event count (316 autistic cases in a cohort of over 500,000) further compounds the problem of sparse data with too many predictors.
Misclassification and Diagnostic Delay Bias
The average age at MMR vaccination was 17 months, but the mean diagnosis age was 4 years and 3 months, meaning many vaccinated children had years of exposure time before a potential diagnosis. In contrast, unvaccinated children tended to be younger and less likely to be diagnosed at all.
They acknowledge that “much of the follow-up for the unvaccinated group involved young children, in whom autism is often undiagnosed”, yet do not correct for this delay in diagnosis.
Conclusion: This leads to immortal time bias and diagnostic latency bias, both of which undercount autism in the unvaccinated group. Their claim that this somehow did not affect the results is scientifically untenable.
Read the rest here.
Comments
One response to “What’s Wrong with “The Danish Study”?”
there are two issues I have here. The first is that the rate of autism has continued to rise. Yet, supposedly, the number of MMR vaccines administered has been the same year to year. So, that doesn’t make sense. That is unless, number two, they have been changing the formulation of the MMR vaccine or some other product given to children.
As a matter of course, there are regulations for notifying the FDA anytime you change the ingredient, the process or the equipment used to make the product. There could be exceptions, but this is an issue that needs investigation.
If it turns out that it is an FDA approved product to blame for this, then there is a conspiracy theory to consider. The FDA and drug companies could be weaponizing products to induce autism. There is animal research on inducing autism-like conditions, so this angle should be investigated as well.