Taiwan valuation river — the bands are rebuilt from snapshots, and the window defines the width
The standard misreading of a river chart is to read the position of the price inside the bands as a verdict of cheap or expensive. This page deliberately refuses that verdict. The bands are rebuilt from historical snapshots: a five-year window gives one band, a ten-year window another, and neither is truer — one simply has its window written down. The denominator matters more still: PE divides by earnings, PB by book value, yield by dividends. A price at the lower band does not mean the stock is cheap; the denominator may be deteriorating and the price merely following it down. So we print the window, the percentile definition and the denominator basis next to the bands instead of answering whether it is cheap now.
What the fields are: eight bands and their definitions
The endpoint /v1/indicator/river/{stock_id}?metric=pe|pb|yield returns eight percentile bands alongside the price series, each carrying the history window length, the percentile definition, the denominator basis (single quarter, cumulative or trailing four quarters) and the as-of date. The metric selects price-to-earnings, price-to-book or dividend yield.
Eight bands are simply one way of slicing a historical distribution. How many slices to cut is a choice, not a natural scale; change the slicing and the same price lands in a different band — the price did not move, the ruler did.
Snapshot rebuilding and the absence of look-ahead
Bands are rebuilt from the snapshots that were actually available on each day, never from later-revised figures. The purpose is narrow: to avoid using what is known today to look at the past, which would make historical bands appear sharper than anyone could have computed at the time.
When fewer than 20 trading-day snapshots exist, the endpoint returns 404 and does not extrapolate or fill. Bands drawn from a handful of points give a false sense of stability; we would rather return nothing than a line that merely looks credible.
Why sitting at the lower band is not an entry
A percentile is a percentile of a ratio, and the ratio is set jointly by its numerator (price) and denominator (earnings, book value, dividends). A price arriving at the lower band may mean the price fell, or may mean the denominator is deteriorating; in the second case the band itself will keep sliding down in the days that follow.
So a claim such as "below the band means it is cheap" will never appear here, because the bands cannot support it. All the bands can say is where the current ratio sits within the historical distribution, under this window and this definition.
What this page must not be used for
No price forecasts, no target prices, no entry or exit timing, no ranking, no screening. To be explicit: the band does not predict the price; it describes a distribution of past ratios, not a probability over future prices.
The right use is as a starting question: where does the current ratio sit within this window, what industry cycle does the window cover, and what happened to the denominator in the latest period? The answers live in the statements and in the window definition, not in the colour of a band.