**PURPOSE**- Averages 2 or more files, computing measures of variance (per point, total, etc.). The average and the variance images can optionally be stored in output files. Optionally can split image set into two even-odd subsets and compute averages and variances for the subsets. Works for images and volumes. Example.

**SEE ALSO****AS R**[Average image/volume series, optional subset] **AS F**[Average images - find statistics & ' *'Q'*' factor map ||]

**USAGE**- .OPERATION: AS S

- .INPUT FILE TEMPLATE (E.G. PIC****): PIC***

[Enter name of image series to be added. Astericks in the template will be replaced by numbers solicted next.].SELECTION DOC. FILE NAME OR LIST OF FILE NUMBERS: 1-10,12

[Enter numbers of files within the series to be added. The file numbers can also be read from a selection document file where file numbers are contained in the first register (not the keys).][Following option menu appears.]

MENU:

A AVERAGE AS AVERAGE WITH SUBSET AVERAGES V VARIANCE VS VARIANCE WITH SUBSET VARIANCES AV AVERAGE AND VARIANCE AVS AVERAGE AND VARIANCE WITH SUBSETS .MENU OPTION (A/AS/V/VS/AV/AVS): AVS

[Enter the desired output option.] - If option 'A', 'AS' or 'AVS' was specified the following prompt appears:

.AVERAGE FILE: avg

[Enter name of output file receiving average.]- If option 'AS' or 'AVS' was specified the following prompts appear:

.AVERAGE FILE FOR FIRST SUBSET: avg1

[Enter names of output file receiving subset 1 average.].AVERAGE FILE FOR SECOND SUBSET: avg2

[Enter names of output file receiving subset 2 average.]- If option 'V', 'VS' or 'AVS' was specified the following prompt appears:

.VARIANCE FILE: var

[Enter name of output file receiving variance map.]- If option 'VS' or 'AVS' was specified the following prompts appear:

.VARIANCE FILE FOR FIRST SUBSET: var1

[Enter names of output file receiving subset 1 variance.].VARIANCE FILE FOR SECOND SUBSET: var2

[Enter names of output file receiving subset 2 variance.]Various statistics are printed out such as:

Number of images

Number of elements (pixels)

Average of average image

Variance of average image

Total variance

Total std. deviation

Variance. per point

Std. deviation per point

**NOTES**

- The variance estimator can be used for statistical tests.

**SUBROUTINES**- ADDS_N

**CALLER**- UTIL2

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