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Time series
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Use the 'Plot time series' button to generate 18 scatterplots. For each, the sample value (X - coordinate) is plotted against the sample value at a fixed time increment in the future (Y -coordinate):
back to topIn each plot the time increment is equal to the start lag plus the sum of the cumulative time steps (i.e., start lag + time step X plot number). The increment value is shown at the top of each plot. If there is no temporal predictability, the point distribution will be random. However, if temporal patterns exist, the distribution of points will be non-random, and the shape of the distribution will indicate the degree of symmetry and the scatter will indicate the degree of randomness or 'noise'. You can replot with different start lags and time step increments. Click the 'Print plots' button for hard-copy output. Note that 24, not 18, time steps are plotted, and that you cannot select this button until data have been plotted on the screen.
• Use the 'periodicity test… ' button to generate a summarized periodicity test for 50, 100, 200, or more stepped time intervals (NOTE: the interval selection buttons are only available if there are sufficient points within the block). For 200 or fewer steps, results are shown as a bar graph; for more steps a line plot is drawn. This is the setup screen for generating a periodicity test:
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Output from a typical periodicity test looks like this:
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This example shows a 250-step plot. Correlations with negative slopes are plotted below the zero line. Bar (or line) heights are a relative index of how value at time ( T ) predicts value at time ( T + time step). The tallest bar (red on color screens) is the interval with highest predictability. Click the 'Print' button for hard-copy output; click the 'Quit' button, another window, or the close box to return to the analysis page.
The iterative sampling process starts at an initial point (a particular sample) in the file, then steps forwards and backwards by user-defined intervals (the 'skip' interval) and takes the mean, range, and SD of blocks of data of user-set duration, symbolized as:
-------||||||||-------|||||||--------|||||||-------||||||||-------
where ----- = skipped samples, ||||| = blocks, and | is the initial point
This process is repeated until user-defined limits are reached, or the start of end of the data are reached. The initial point can be a user-set sample number or the central point in a data block (for example, you could search for the highest point in a data file, use the 'set block' option, and then use the resulting block as the initial point). If a block is selected, the start and end points are set to the beginning and ending points of the block. The default value is 1/2 of the total number of samples. The control window looks like this:
When ready, click either the "delta-t step plot" button or select a new channel to display results, as in the following example:
Results are plotted on-screen (blue for measurements later than the initial point, red for measurements earlier than the initial point, and gray for the mean value for both + and - values at a given interval).
The 'scatterplot' button shows an X-Y scatterplot of step-sampled data from any two of the available channels (it's only available if there are 2 or more channels in the file).
You can use the channel buttons to select up to 10 channels that can be analyzed and stored in a tab-delineated (Excel compatable) file with the "save as ASCII" button. Note that you can select more than 10 channels, but only results from the first 10 will be stored. If the file contains interpolated data as indicated with the standard interpolation markers "»" and "«", any stored values that were computed from interpolated data will be marked in the Excel file.
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