Sentiment is not directly observable like a transaction hash. Providers estimate it from selected inputs, which can include price momentum, volatility, surveys, search activity, or social posts. Alternative.me publishes the ingredients and intended interpretation of its Fear and Greed Index. A score therefore reflects both market behavior and methodological choices. Two providers can report different numbers on the same day without either having measured an identical population or concept.

Imagine index A measuring Bitcoin volatility and momentum, while index B classifies posts about small-cap tokens. A nervous Bitcoin market and enthusiastic token community could produce opposite readings. Comparing their scores as if both represented all cryptocurrency investors would be misleading. Useful metadata includes the covered assets, sampling window, update time, input weights, missing-data handling, and whether revisions change previously published observations. Changes to methodology can also break comparisons with older values.

An index describes its inputs; predicting future returns is a separate claim that needs testing. Price-derived components may simply restate a move that already happened. Social inputs can be distorted by coordinated promotion, bots, and selection effects. Evaluate predictive claims using data available at the time, transaction costs, and genuinely separate test periods. A low or high number alone is not proof of undervaluation, an imminent reversal, or a reliable timing strategy.