Missing Price Data Can Create False Stock-Chart Spikes

Summary

The document asks why a five-year stock-price chart contains frequent, brief spikes. The answer attributes them to missing observations in the displayed data: according to the response, the data provider represents unavailable prices as zero. When a chart connects those zero values to valid prices before and after them, it can display sharp artificial movements that do not represent actual trades or market behavior.

This is a useful data-quality explanation for anyone inspecting historical prices or preparing market data for analysis. The exchange offers no independent verification, diagnostic procedure, or comparison with another data source, so the claim should be treated as an explanation of the particular chart rather than a general rule about all providers. The practical lesson is to check how missing observations are encoded before interpreting extreme chart movements or using the series in a backtest.

Key ideas

• Missing observations encoded as zero can produce artificial price spikes in charts.
• A charting system may connect zero-valued gaps to surrounding valid prices.
• Check how a data source represents missing prices before interpreting extremes or backtesting.

Tags

# Why would a stock price have frequent very short, very high spikes?


# Why would a stock price have frequent very short, very high spikes?












If I look at the five year price for GML on Yahoo Finance: https://finance.yahoo.com/quote/gml/

I see many strange spikes:

What could cause such behavior?

## Answer by Valometrics.com (score 1)

https://quant.stackexchange.com/a/50896

Actually, it is missing data. I've got a look on YAHOO Finance, the price was set to ZERO when no data is available. That's why you are seeing spikes on the graph.

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