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Withdrawing quantities from the adjustment

 

In the same way that we can introduce additional quantities into the adjustment, so too can we determine the effects of withdrawing quantities from the adjustment. We might do this for various reasons,gif but here particularly for the purpose of investigating the rather peculiar nature of the specifications over tex2html_wrap_inline8550 and its observed value tex2html_wrap_inline8768 .

When we remove tex2html_wrap_inline8546 from the adjustment at this stage, it as though we are left with a simple adjustment of tex2html_wrap_inline8554 by tex2html_wrap_inline8550 . In addition, we also learn about the partial adjustment of tex2html_wrap_inline8554 by tex2html_wrap_inline8552 . Some of the results of this partial adjustment are worth further consideration as follows. The resolutions for the adjustment by tex2html_wrap_inline8550 and for the partial adjustment removing tex2html_wrap_inline8546 are:

eqnarray1187

showing - as we suspected - that tex2html_wrap_inline8550 alone is not a good source of information: its effect is at best to reduce uncertainty by less than 5%; and that most of the information is contained wholly in tex2html_wrap_inline8546 : when we remove tex2html_wrap_inline8552 we also remove nearly all of our capability to reduce uncertainty in tex2html_wrap_inline8554 .

The evaluated adjusted expectations for the adjustment by tex2html_wrap_inline8550 solely are

eqnarray1198

representing fairly large changes ( tex2html_wrap_inline9484 standard deviations) from the initial values of 4.16 and 6.25 respectively. Although these are fairly large changes, they correspond to only small reductions in uncertainty about tex2html_wrap_inline8580 and tex2html_wrap_inline8582 . Informally it is as though the prior and posterior distributions for tex2html_wrap_inline8580 and tex2html_wrap_inline8582 are quite flat, so that large changes in expectation can correspond to small changes in uncertainty.

  figure4664
Figure 3:  Sizes for the adjustments tex2html_wrap_inline8550 and tex2html_wrap_inline8552

The sizes of the adjustments are shown in figure 3 and display two remarkable features. Firstly, the size ratio for the simple adjustment by tex2html_wrap_inline8550 is more than five times as large as expected; and secondly the size ratio for the partial adjustment after adjusting by tex2html_wrap_inline8546 additionally is very much smaller than expected. The former feature is more or less expected, given the sizes for the similar adjustment shown in figure 2. The latter feature may be interpreted as showing that a partial adjustment by tex2html_wrap_inline8546 in addition to tex2html_wrap_inline8550 is expected to enable changes in expectation that simply don't materialise.

Comparing figure 3 with figure 2, we see a size ratio of tex2html_wrap_inline9506 for the simple tex2html_wrap_inline8550 adjustment, and a size ratio of tex2html_wrap_inline9510 for the partial adjustment by tex2html_wrap_inline8548 . Thus, the size ratio for the simple tex2html_wrap_inline8550 adjustment is larger than the size ratio for the adjustment where tex2html_wrap_inline8546 has been extracted. This might suggest that although we have identified tex2html_wrap_inline8550 (with its observation tex2html_wrap_inline8768 ) above as having some peculiar features, this is also true of the portion of tex2html_wrap_inline8546 that is common to tex2html_wrap_inline8550 .


next up previous
Next: Review of the example Up: Adjusting beliefs in stages Previous: The bearing and path

David Wooff
Thu Oct 15 12:20:04 BST 1998