Compact and average

  •   COMPACT & AVERAGE...      Makes a compact version of the data by breaking it into a series of blocks of user-specified length (with length specified either in terms of number of samples, or of duration), and then computing a mean and S.D. for each of the blocks.  Each block contains a fixed number of cases. If you use the Sample averaging option, the block duration (in time units) depends on this number and the sample interval.   If you use the Time averaging option, the number of samples averaged depends on your specified duration and the sample interval.   Depending on the sample interval the duration may not be exactly what you specify, but the program will do its best.   For example, if you sampled every 3 seconds and you want a block duration of 40 seconds, the program will use 39 seconds (since 3 does not divide evenly into 40).

  • Compacted data can be saved as tab-delineated text files containing both means and standard deviations.  It is also shown on-screen in the regular plot area.  This can make it easier to see trends in noisy data, and is also useful for preparing data for publication -- a figure broken into a series of means and S.D.s is frequently easier to read than a simple line plot (particularly if the raw data are somewhat noisy).

    NOTE:  although the plot area on the screen shows the compacted version, any analyses are performed on the original data, which is shown as normal in the block window.

    The first example shows a 20-fold sample averaging compaction, which equates to a 'block size' of 30 seconds for each mean and S.D. computation.  The 'highlight data means' and 'show S.D.' options are selected; this will show the mean values as a dot, and the SDs as vertical lines in the plot area (in active screen mode only if there are more than screenwidth cases).

    The second example shows a 60-second time averaging compaction, which equates to a 'block size' of 30 samples for each mean and S.D. computation.  The 'highlight interval means' and 'show S.D.' options function as described above for sample averaging compaction.   Note that in this example the sample interval was 2 seconds, but the user entered a desired interval of 60.1 seconds to get the necessary 30-sample average (this apparent inconsistency is due to the way floating-point arithmetic is handled).

    A warning message will appear if the selected compaction interval is too short (< 1 sample interval) or too long (the compaction interval is more than 20% of the file duration).  Close the warning window or click the Compaction window to dismiss the warning.

    Some operations, like Baseline with user-selected points, are difficult to use if the data are shown in compacted form (although you can still read the uncompacted values for the cursor position in the data bar).  It's probably best to shift to the regular display ('normal plot') for these operations.

    go to: