Market Internals: TICK, TRIN and Breadth, Tested on Sector Counts Since 1998
Market internals are readings built from all the stocks on an exchange rather than from an index price, such as the NYSE TICK, the TRIN or Arms index, and the count of advancing against declining issues. Traders use them to judge whether a move in the index is broad or carried by a few large stocks.
Market internals are the numbers that look underneath an index: how many stocks are rising, how many are falling, how many just traded up or down, and where the volume went. The best known are the NYSE TICK, the TRIN and the advance-decline count. This page sets out the exchange definitions, works the TRIN arithmetic on real volumes, and measures what breadth told SPY traders from 1998 to September 2026.
How it forms
An index can move on a handful of stocks. The S&P 500 is weighted by company size, so a strong day in its largest members can lift it while most of the other stocks fall. Internals count the members instead of weighing them.
Each reading counts something different. Advancing and declining issues compare every stock with its prior close. TICK compares every stock’s last trade with the trade before it, so it changes by the second. TRIN brings in volume, asking whether the shares traded went mostly to the rising stocks or the falling ones.
Traders read them against the index. A rising index with most stocks rising is called broad. A rising index with most stocks falling is called narrow, and the reading traders give is that a narrow move has less behind it. The data below tests that reading on the breadth that can be computed for free.
The official definitions
TICK. Nasdaq’s glossary, read on 26 September 2026, describes the tick indicator as a count based on how many stocks last traded on an uptick against how many last traded on a downtick, used as a sentiment gauge. The closing tick is the same net count taken at the close.
TRIN, or the Arms index. The same glossary gives the usual formula: advancing issues divided by declining issues, with that result divided by advancing volume over declining volume. It reads a value below 1.0 as bullish and above 1.0 as bearish, and notes the index is often smoothed with a simple moving average.
Advance-decline and breadth. Nasdaq defines the advance-decline ratio as advancing stocks divided by declining ones over a period, and breadth as the share of stocks advancing against those unchanged or declining. The running total of advancers minus decliners is the advance-decline line, which the McClellan Oscillator smooths.
What the free data did not include. On 26 September 2026 the Yahoo Finance chart API returned no data for the symbols ^TICK, ^TRIN, ^ADD, ^ADV, ^DECL, ^NYAD, ^TICKQ and ^TRINQ. So no TICK or TRIN history is charted or estimated here. The tests below use breadth that can be computed honestly from bars that were available.
A worked example
Friday 25 September 2026, nine sector funds. The nine original Select Sector SPDR funds cover materials (XLB), energy (XLE), financials (XLF), industrials (XLI), technology (XLK), consumer staples (XLP), utilities (XLU), health care (XLV) and consumer discretionary (XLY). The later real estate (XLRE) and communication services (XLC) funds are left out because their history is much shorter. On the day, eight closed above their prior close. Only energy fell, from $62.60 to $62.04, a drop of 0.89%. The gains ran from 0.22% for consumer discretionary through 0.24%, 0.38%, 0.44%, 0.49%, 0.57% and 0.80% to 0.95% for industrials. SPY rose 0.54%.
The breadth arithmetic. Eight advancing and one declining gives an advance-decline ratio of 8.0. The eight rising funds traded 103,425,700 shares between them, and XLE alone traded 37,559,500. The volume ratio is 103,425,700 divided by 37,559,500, or 2.75.
The TRIN arithmetic. 8.0 divided by 2.75 is 2.91. By the glossary’s reading, anything above 1.0 is bearish, yet eight of nine funds rose and so did SPY. The reason is share volume: XLE traded more shares than any other fund that day, and a fund’s share count depends partly on its price per share. This is the glossary formula applied to nine funds, not the NYSE TRIN, and it shows how one heavy-volume decliner can swing the reading.
The original data
6,981 sessions of sector breadth. From 23 December 1998 to 25 September 2026, each session is scored by how many of the nine funds closed above their prior close, 0 to 9. Closes are split-adjusted and not dividend-adjusted. All nine rose on 913 sessions and none rose on 823. Every session is in the sector breadth file, with SPY’s move that day and the next.
It described the day almost perfectly. SPY rose on all 913 sessions when all nine funds rose, and fell on all 790 sessions when all nine fell. With 6 or 7 funds up, SPY rose 89.2% of the time; with 0 or 1 up, 0.9% of the time.
It said little about the next session. Across all sessions, SPY closed higher the next day 3,758 times in 6,980, 53.8%. By breadth: 0 or 1 funds up, 815 of 1,458 (55.9%, p = 0.115); 2 or 3 up, 653 of 1,184 (55.2%, p = 0.366); 4 or 5 up, 658 of 1,261 (52.2%, p = 0.247); 6 or 7 up, 747 of 1,401 (53.3%, p = 0.708); 8 or 9 up, 885 of 1,676 (52.8%, p = 0.405). None is far enough from 53.8% to separate from chance.
Narrow days were not a warning either. On 180 sessions SPY rose while 3 or fewer funds rose. The next session was higher 96 times, 53.3% (p = 0.94). On 155 sessions SPY fell while 6 or more funds rose; the next session was higher 88 times, 56.8% (p = 0.47).
Breadth at 10:30
An intraday test on 30 large stocks. Day traders read internals during the session, so the hourly bars were used too: at 10:30, the close of the first hourly bar, how many of 30 large US stocks (AAPL, MSFT, AMZN, GOOGL, META, NVDA, TSLA, JPM, BAC, WFC, XOM, CVX, KO, PEP, PG, JNJ, PFE, MRK, UNH, HD, WMT, COST, DIS, NFLX, INTC, CSCO, ORCL, IBM, BA and CAT) were above their prior close. The outcome is whether SPY’s official close finished above its 10:30 price. 723 full sessions, 27 October 2023 to 25 September 2026.
No level stood out. SPY finished above its 10:30 price on 402 of 723 sessions, 55.6%. With 0 to 6 stocks up at 10:30 the share was 20 of 32 (62.5%, p = 0.48); 7 to 12, 92 of 168 (54.8%); 13 to 17, 133 of 245 (54.3%); 18 to 23, 130 of 225 (57.8%); 24 to 30, 27 of 53 (50.9%). The groups at the edges are small. The full list is in the intraday breadth file.
When it fails
One heavy fund or stock swings the volume readings. The TRIN of 2.91 on a day when eight of nine funds rose shows how a single decliner with high share volume can outvote the rest.
Breadth is a description, not a forecast. On these counts it matched the same day almost exactly and matched the next day no better than chance.
These are stand-ins for the real series. Nine funds and 30 stocks are not the full list of NYSE issues that TICK and the advance-decline count cover, and a result on one does not prove a result on the other.
The divergence story needs its own count. A narrow rally sounds fragile, and on nine funds since 1998 the session after one was higher 53.3% of the time, close to the everyday rate.
Related
The McClellan Oscillator turns daily advancing and declining counts into a smoothed breadth reading. The sector ETF page covers the funds used here to split the market. And market trend covers the price side that internals are usually read against.
Read internals as a description of the session you are in, not a forecast of the next one. When I check breadth, I use it to ask whether a move in the index is broad or narrow, and I size the trade for being wrong either way.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.