Need Question Answered

[Steven L. Wertheim]

>>On 6 May 93 ltorre at eis.calstate.edu asked:
>>>Can someone out there help me distinguish between the scientific terms:
>>>		-Accuracy
>>>		-Reliability
>>>		-Validity

>In article <9305080126.AA59210 at itsa.ucsf.EDU> jharper at ITSA.UCSF.EDU (M. Jane Harper) writes:
>>
>>"Reliability" means the extent to which an
>>instrument reproduces results given the same analysand.  In other words, if
>>you and I (or Machine A and Machine B) rate someone (or some thing) on a
>>characteristic and we get identical or closely correlated results, the tool
>>we used to perform the rating has a high reliability.  
>>"Validity" is a related
>>concept which refers to the extent to which an instrument measures what it is
>>intended to measure.  If I stick a thermometer in someone's mouth, I will get
>>a temperature, not a blood pressure; the thermometer is a valid measure of
>>temperature and an invalid measure of blood pressure.
>>

In article <1993May10.210403.4926 at alw.nih.gov> arm at helix.nih.gov (Andrew Mitz
) writes:>
>Good answer.  Let me add that sometimes Accuracy is used to distinguish from
>precision.  In this case, precision means the same as "reliability" as defined
>above.  Accuracy would mean the difference between a measurement and the
>actual value being measured.


Just one more clarification to the many excellent reponses.  Precision is the
smallest numerical gradation that a device can measure.  This says nothing
about its accuracy.  If the thermometer above has a marking every .1 degrees,
but has the wrong amount of mercury inside, it still has .1 degree precision
even though it may be (reliably) several degrees off (inaccurate).

Steve


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Steven L. Wertheim, Ph.D.                       Internet: stevew at athena.mit.edu
Harvard Medical School                         Voice-net: (508) 624-8117 
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