Biomedical Engineering Reference
In-Depth Information
2.
U
NCERTAINTY
(Almost) Everything is Uncertain .........................................................13
Uncertainty and Error ..........................................................................14
Random and Systematic Errors ............................................................15
Precision vs. Accuracy .........................................................................16
Levels of Confidence.............................................................................16
One-tailed comparisons...........................................................................18
1.5 standard deviations............................................................................19
Asymmetric uncertainties .......................................................................19
Combining Uncertainties......................................................................20
Representation of the distribution of uncertainties by a single number.....18
Uncertainty Must be Made Explicit......................................................20
How to Deal with Uncertainty..............................................................21
The measured or calculated values of almost all quantities of interest
in radiation oncology (and in most other walks of life) cannot be
known exactly, but have some degree of uncertainty associated with
them. The exceptions are the so-called “denumerable” quantities -
things which can be counted such as the number of digits on your
right hand. The analysis of the uncertainties in non-denumerable
quantities is not an academic exercise, but, rather, is central to the
conduct of radiation therapy - not least because it is a life or death
matter for patients. As you will see, the following chapters are
suffused with talk of uncertainty and the need to estimate it. It is for
this reason that I have placed this chapter near the beginning of this
topic.
While there are very many excellent topics on the application of
statistical analysis in medicine, I can recommend Mould (1998) as
being particularly clear and succinct.
(A
LMOST
)
E
VERYTHING IS
U
NCERTAIN
Each of the following important components of radiation therapy has
many aspects with a significant level of uncertainty:
13
