Detrended Fluctuation Analysis (DFA) is a method used to analyze time series data to determine if it has long-term correlations or patterns. 

A time series is a series of data points collected at regular intervals over time, such as daily stock prices, monthly rainfall, or yearly temperatures. When analyzing time series data, it's important to determine if there are patterns or trends that persist over time or if the data is simply random noise. 

DFA is used to detect the presence of long-term correlations, also known as "long-memory processes". These long-term correlations mean that the data is not just random noise, but has some underlying pattern or structure. 

The term "statistical self-affinity" refers to the property of a time series where its statistical properties remain unchanged when the data is rescaled by a factor. For example, if we zoom in on a portion of the time series, it should look similar to the original time series, just with a different scale. 

DFA works by dividing the time series into overlapping segments, detrending each segment to remove any linear trends, and then calculating the root-mean-square fluctuation of the detrended data. By analyzing the relationship between the length of the segments and the root-mean-square fluctuation, DFA can determine if the time series has long-term correlations.

For example, if we analyze a stock's daily closing price over a period of 10 years, DFA could be used to determine if the stock price has long-term correlations or if it's just random fluctuations. If the stock price has long-term correlations, it could indicate that there are some underlying factors driving the stock price over the long-term.
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