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Debt three deviations from the mean — the silent alarm of August 2015

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The extreme

Some series swing so much that a large deviation barely surprises. Public debt as a share of GDP is not one of them. It moves slowly, month by month, and rarely jumps. That is why, when public indebtedness marked a deviation of 3.01 against its own history, the signal weighed more than the number suggests. In a gauge that measures a stock, not a mood, three deviations is not a market scare — it is a fracture that had been building up becoming visible all at once. In numbers: public debt at 62.97% of GDP, a reading of 3.01 — one of the widest departures ever recorded in the series.

What happened next

The difference between this alarm and the others of the same month is time. In the exchange rate, which marked a similar deviation (3.16), the number can reverse within weeks. A stock of indebtedness cannot: it climbs by accumulation and only eases by accumulation. The backdrop did not help undo it — the economy combined recession with stubborn inflation, and the Selic pinned at 14.25% a year anchored neither the currency nor fiscal confidence. A high rate at its limit, and the patient not responding.

What did not happen

Debt three deviations out was not, by itself, a prophecy of collapse. A high z measures rarity, not destiny. And it was not an isolated number: in the same month, the exchange rate (3.16) and a fiscal-tension gauge (3.06) also broke through the band. A lone deviation can be noise; three independent series above 3.0 at the same time is a regime. But debt itself did not "explode" that August — it merely made legible, in a single digit, what had been writing itself for months.

The honest verdict

Three deviations in a slow series say more than three deviations in a volatile one: it is not a scare, it is structure. Debt at 62.97% of GDP did not announce what was coming — it recorded what already was.

Continue reading: The three alarms of August 2015 · When a deviation becomes an anomaly · The 2015 crisis and the 2016 bottom →

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Characters: Structure (intermarket) · Flow (risk appetite)