Time series (periodicity tests)

BASIC TIME SERIES... This option displays time series data in graphical form. Time series analysis examines data for many kinds of temporal relationships -- basically, does sample value at a particular time ( T ) predict sample value at some later time ( T + K )? A graphical display is useful for determining if there are periodicities within the data, and (if periodicities exist) if the waveforms are symmetrical. When this option is selected, LabAnalyst opens a window containing edit fields for the Start Lag (the initial time increment between samples) and the Time Step (the time increment added for each successive plot). Defaults are a start lag of 0 and a time step of 1 sample. Edit as desired. There are two plotting options:

The 'periodicity test… ' procedure generates 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:

Output from a typical periodicity test looks like this:

This example shows a 750-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 'Show Other Peaks Where...' button to display only those time correlations with r² higher than a specified value. Click the 'Print' button for hard-copy output; click the 'Quit' button, another window, or the close box to return to the analysis page.

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