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What is a Stock Index?

When the news says "Oslo Stock Exchange rose 1.2% today" — what does that actually mean? They are talking about a stock index. An index measures the performance of a group of stocks and serves as a thermometer for the entire market. Here we explain everything you need to know.
📅 28. April 2026 👁️ 4 views 📂 Grunnleggende 🇳🇴 Les på norsk

The market's thermometer

There are thousands of stocks on the world's stock exchanges. It would be impossible to follow all of them simultaneously. Stock indices solve this problem — they gather a selection of stocks into one single measure that tells you how the market as a whole is moving.

An index is simply a basket of stocks — and the basket has a combined value that rises and falls in line with the stocks inside it.

"The one who sees the forest and not just the trees always makes better decisions." — Florence Scovel Shinn

The most important indices you should know

OBX
Oslo Stock Exchange's most important index. Contains the 25 most traded stocks on the Oslo Stock Exchange. When Norwegian news talks about "the exchange" it is usually OBX they are referring to.
S&P 500
The 500 largest listed companies in the USA. The world's most important stock index — when S&P 500 sneezes, the rest of the world catches a cold. Apple, Microsoft, Amazon and Alphabet are among the largest.
Nasdaq 100
The 100 largest non-financial companies on the Nasdaq exchange. Dominated by technology companies. More volatile than S&P 500 — rises more in bull markets, falls more in bear markets.
MSCI World
Over 1,500 companies from 23 developed countries. The global index used by many international funds. If you invest in a global index fund it often follows this one.
Tip: Compare your portfolio return against a relevant index. In BørsArena you can see the leaderboard — that is your benchmark against other participants!
"The world belongs to those who see opportunities where others see limits. Limits exist in the mind — not on the map." — Florence Scovel Shinn

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