Spearman-Brown Prophecy Formula

[Humphrey Paulie]

Hi there,
  I have used Spearman-Brown Prophecy formula to compute the times a test should be lengthened to boost its reliability from 0.88 to 0.95.
  I have found k=259 !!.
  It's a bit large. I can't believe it.
  I'd be thankful if someone does the calculation and confirm or disconfirm my calculation.
  Thanks in advance
  Humphrey

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[Dubois, Marty A.]

 Humphrey,

  I got N = 2.59 vs your 259.

Marty

Marty Du Bois
Research Analyst
Community Health Assessment Unit
Community Epidemiology Section
Community Health Services
Lake County Health Department/Community Health Center

3012 Grand Ave.
Waukegan, IL  60085