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<p>Right. Several things happened to increase the East Asian (which for present purposes means mostly Chinese and Korean) numbers in that time. There are different patterns for Indians and Vietnamese, and other groups that are ethnically or geographically East Asian (Japanese, Filipino, etc.) are not even remotely comparable to the big 3 in their numerical representation or apparent interest in the contests. </p>
<ol>
<li><p>More Asians (per capita) of high school age. Many are scientists’ children at elite high schools, or hooked up to local universities where mom/dad works.</p></li>
<li><p>Qualification became relatively easier. Number of USAMO qualifiers is 500 instead of 100.</p></li>
<li><p>USAMO and IMO became more trainable (and consequently more difficult in absolute terms). Problem books, databases and contest-focused math web sites have proliferated since 2000.</p></li>
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<p>3b. As a result, starting early became more important for those wanting to reach the high echelons. Since Asians on average start their childrens’ math education earlier and/or more intensively, there are relatively more Asians who have enough time to reach the ever-increasing training levels needed to reach USAMO and beyond. </p>
<ol>
<li>Word of the association between olympiad success and elite college admission has reached the Chinese and Korean immigrant communities.</li>
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<p>4b. As a result, dozens of math olympiad schools (some conduct classes in Chinese or Korean) and math olympiad camps (published attendance figure from the first year of a camp run by ex-US IMO coach: 80+ percent Asian) have opened in the past 5-8 years. A few are oriented toward Russian or Indian immigrants but the vast majority of olympiad schools are started by East Asian immigrants and pitched to East Asian parents. </p>
<p>4c. At the high end one could count Philips Exeter as a special program of this kind, producing one or more E.Asian winners of the USAMO or IMO each year. Of the 20+ USAMO qualifications from Exeter in the past two years, 100 percent are Asian. The US IMO coach, Zuming Feng, is an instructor at Exeter, and apparently Asian parents are using Exeter as an olympiad school at a much higher rate than whites.</p>
<p>Equivalent factors don’t operate after elementary and high school, and as a result one would expect some deterioration of the Asian percentages as time and selectivity levels increase along the academic “pipeline”. For example: </p>
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<li>70+ percent East Asian winners of the 8th grade olympiad (Mathcounts) > 50-60 percent of USAMO qualifiers > 20-30 percent of Putnam competition winners (top 50-80). In odds-ratio terms (relative chances of a white vs an Asian math star to be a math star four years later) these declines are huge. It’s not because the math tests are culturally biased against Asians, and it’s not because Asian competition winners are radically likelier than whites to switch their interests to other subjects.</li>
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