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APPENDIX

Teachers’  College,  are  a  great  convenience  for  the  beginner.
A  comprehensive  treatment  may  be  found  in  E.  L.  Thorndike’s
“Mental  and  Social  Measurements”  and  a  very  concise  presentation ­
  in  Guy  M.  Whipple’s  “Manual  of  Mental  and  Physical ­
  Tests  ”,  Vol.  I.  The  practical  psychologist  will  find  that
the  slightly  greater  accuracy  of  the  Pearson  formula  is  more
than  compensated  for  by  the  greater  flexibility  and  simplicity
of  the  Spearman  formula.  It  takes  about  six  times  longer  to
work  out  the  Pearson  formula  than  the  Spearman  formula
(differences  squared).  In  the  treatment  of  employment  tests
it  is  much  more  important  to  obtain  a  large  number  of  correlations ­
  than  to  spend  time  trying  to  increase  the  refinement  of
a  few.  Two  indices  in  which  there  is  an  inaccuracy  of  even  5
points  have  a  greater  practical  significance  than  one  correlation ­
  which  is  absolutely  accurate.
Where  groups  of  more  than  20  rankings  are  to  be  compared,
the  Spearman  “footrule”  is  sufficiently  accurate,  and  extremely
convenient.  Extensive  use  of  this  formula  was  made  in  the
course  of  the  experiments  described  here.  Where  “  n”  was  less
than  20,  the  longer  Spearman  formula  was  used.
Probable  errors  are  not  given  in  connection  with  the  indices
of  correlation  in  the  body  of  the  book  for  two  reasons:  first,
because  they  would  confuse  the  ordinary  reader;  secondly,  the
practical  psychologist  can  tell  almost  at  a  glance  what  the
probable  error  is.  Knowing  the  number  of  individuals  and  the
size  of  the  correlation,  the  P.  E.  can  easily  be  deduced.
B.  GENERAL  PROCEDURE
When  an  individual  applies  for  work,  his  application  is  taken
in  the  employment  office  and  the  information  placed  on  a  permanent ­
  employment  record  card.  This  card  is  then  taken  into
the  psychological  examination  room  where  it  serves  as  an  announcement ­
  of  the  applicant’s  readiness  to  be  examined.  It
also  tells  the  examiner  the  kind  of  work  for  which  the  applicant
is  asking  and  gives  him  certain  other  essential  information.