For Denmark, you probably have consistent medical records, free medical care (adding to consistency), and a homogenous population. Which is worth a lot for trying to do a large scale retrospective. Now Denmark is probably not that unique vs Sweden/Norway/whatever, but any country in the region probably is ripe for statistical analysis.

> Many (obvious) questions:

The paper linked in the Ars article answers most of your questions.

> Why Denmark?

The article itself answers it. The lead author has access to a large database with relevant information - Denmark's national registry of medical records.

> Why that particular time frame?

The paper says this: "Over the past 25 years, the specific vaccines included in the program have changed over time because of policy updates, ... Because the vaccines have varying aluminum content, these uniformly applied policy changes have led to systematically different cumulative doses of aluminum received through childhood vaccination across birth cohorts (mainly before age 2 years). Therefore, these externally imposed systematic variations in aluminum exposure through early childhood vaccination that are independent of individual characteristics provide a natural quasi-experimental framework for estimating the effect of aluminum exposure from early childhood vaccination on health outcomes."

> Why (only) those 50 disorders?

According to the paper: "Incident events of 50 chronic disorders, including autoimmune (dermatologic, endocrinologic, hematologic, gastrointestinal, and rheumatic), atopic or allergic (asthma, atopic dermatitis, rhinoconjunctivitis, and allergy), and neurodevelopmental (autism spectrum disorder and attention deficit–hyperactivity disorder)."

If it isn't abundantly clear, they've selected the sorts of disorders that the antivaxx community alleges that the vaccines (more specifically the aluminum salts in it) cause. They're trying to disprove that claim.

> What of those who left the country? - What of those without access to healthcare? - What of those outside any of the scope? - No mention of any differences of any kind due to gender?

The paper says this: "To be included in our study, children needed to be alive at age 2 years, not have emigrated from Denmark, not have been diagnosed with certain congenital or preexisting conditions (including congenital rubella syndrome, respiratory conditions, primary immune deficiency, and heart or liver failure), and not have received an implausible number of vaccines (Supplement Table 1, available at Annals.org). In addition, we excluded children whose mothers had not lived in Denmark for at least 2 years before childbirth."

They're trying to exclude participants who can introduce possible errors. And the large population would make the results insensitive to such differences. They are attempting to see the overall effects of aluminum, not the difference in how it affects each demographic group.

> Is such a narrow width considered definitive, to the point of considered “squashing”?

Neither the objective nor the subjects are 'narrow width' by any definition. They are studying the relationship of a specific substance (aluminum salts) with specific types of disorders it is alleged to cause. They chose their participants carefully to avoid errors, and still had millions. I believe that this would be conclusive enough, since aluminum salts are alleged to be neurotoxic (which it is at much higher concentrations) and such a toxicity is unlikely to vary significantly between populations around the world.

> And apparently ARS Technica was happy to abandon objectivity and push the accepted narrative.

> I don’t care about the topic one way or another. It’s not the ends, it’s the dark side of the means.

Now this is the part that's frustrating. The narrative about the toxicity of aluminum adjuvants have been pushed around even after being debunked on the basis that infants absorb much more aluminum from their diets than what they accumulate from all their vaccines. The antivaxxers neglect the known facts and resort to emotional appeals to push their narratives, and it has become so desperate that kids are dying of diseases that were once eliminated from the area. It's so widespread that it's occasionally peddled even on HN. And they also keep shifting the goal post. The first component to be targeted without basis was the preservative Thiomersal. But when it was removed from vaccines just to placate the crowd, and was found to not affect the incidence of autism, the target was changed to aluminum adjuvants. Even if the authorities change that for some reason now, the antivaxxers will find some other reason.

And yet, outlets like Ars are accused of 'abandoning objectivity' and 'pushing the accepted narrative' when they try to push back urgently against such falsehoods? Their job is mass reach. The part of objectivity has been taken care of by the researchers behind the paper.