# [Ifeffit] N-idp

Scott Calvin SCalvin at slc.edu
Mon Mar 19 12:04:10 CDT 2007

```Hi Shan,

The aspect you're missing is that the extra data points are not
independent. Suppose you collect data points, with good statistics
(lots of counts per point), at 8.05 and 8.10 inverse angstroms.
Actual EXAFS features don't vary a whole lot over that interval, in
general. So to a good approximation you could interpolate the values
of chi(k) at 8.06, 8.07, 8.08, and 8.09 inverse angstroms. Collecting
data at those points doesn't really tell you much you couldn't figure
out anyway. (To make it a fair comparison, consider collecting 6
seconds of data each at 8.05 and 8.10 inverse angstroms to  2 seconds
of data each at 8.05, 8.06, 8.07, 8.08, 8.09, and 8.10, so that it's
the same total time of collection.)

--Scott Calvin
Sarah Lawrence College

At 05:57 PM 3/18/2007, you wrote:
>Hi All
>
>Greetings. I have a generic question. Does the Number of independent
>points in the data set depend on the step size (in k or E) of the
>scan during data collection? As I see Nidp = (2/pi)*(deltak *
>deltaR), there is no reference to the scan step. In a scan of small
>step size, I would expect a lot more data points than a scan with
>larger step size. But, as per the formula I am left with the same
>number of idp's irrespective of the scan step.
>
>Am I missing something?
>

```