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. Author manuscript; available in PMC: 2012 Oct 9.
Published in final edited form as: School Psych Rev. 2012 Fall;41(1):3–22.

Table 1.

Technical Adequacy of Concordance-Discordance Method

Ignorable
Differencea 		Important
Differenceb 		Base
Rate %c 		Sensitivityd Specificitye PPVf NPVg E1h E2i
.01   .25 .6 .51 .85 .02 .99 99.4% 84.4%
  .5 .5 .65 .85 .02 .99 99.5% 84.6%
  .75 .3 .79 .85 .02 .99 99.7% 84.6%
1.0 .2 .86 .85 .01 .99 99.8% 84.6%
1.25 .1 .92 .85 .01 .99 99.9% 84.5%
.05   .25 3.0 .52 .86 .10 .98 97.0% 84.6%
  .5 2.3 .65 .86 .09 .99 97.2% 85.1%
  .75 1.5 .78 .85 .08 .99 98.5% 85.3%
1.0 1.0 .87 .85 .05 .99 99.0% 85.2%
1.25 .6 .93 .85 .03 .99 99.4% 84.9%
.15   .25 8.8 .53 .88 .30 .95 91.2% 84.9%
  .5 6.5 .66 .88 .27 .97 93.5% 86.5%
  .75 4.4 .78 .87 .22 .99 95.6% 86.9%
1.0 2.7 .88 .86 .15 .99 97.3% 86.5%
1.25 1.5 .93 .86 .09 .99 98.5% 85.7%
.25   .25 14.1 .52 .90 .47 .92 85.9% 85.1%
  .5 10.3 .65 .90 .43 .96 89.7% 87.6%
  .75 6.9 .78 .89 .35 .98 93.1% 88.3%
1.0 4.2 .87 .88 .24 .99 95.8% 87.5%
1.25 2.4 .91 .86 .14 .99 97.6% 86.4%
.5     .5 17.9 .62 .94 .71 .92 82.1% 88.6%
  .75 11.9 .73 .92 .56 .96 88.1% 89.9%
1.0 7.1 .81 .89 .37 .98 92.9% 88.8%
1.25 3.9 .85 .87 .21 .99 96.1% 87.2%
.75   .75 14.7 .67 .93 .63 .94 85.3% 89.4%
1.0 8.7 .74 .90 .41 .97 91.3% 88.6%
1.25 4.7 .78 .88 .24 .99 95.3% 87.1%
1.0   1.0 9.5 .69 .90 .42 .97 90.5% 88.1%
1.25 5.1 .74 .88 .24 .98 94.9% 86.9%

Note. These results apply to the 221,285 cases out of 1,000,000 that remained after applying achievement (<90) and mental ability (>69) cutoffs. At the observed level there were 34,465 cases (15.6%) of SLD and 186,820 (84.4%) of Not SLD. This is the same over all latent definitions.

a

Ignorable Difference is the latent z score difference that is small enough to ignore.

b

Important Difference is the latent z score difference that is large enough to be considered a cause of SLD.

c

Base Rate % is percentage of cases in the sample selected for low achievement but of average mental ability classified as SLD at the latent level.

d

Sensitivity is the proportion of true SLD cases identified as such by the method.

e

Specificity is the proportion of true Not SLD cases identified as such by the method.

f

PPV is Positive Predictive Value or the probability of being truly SLD given a positive test result.

g

NPV is Negative Predictive Value or the probability of being truly Not SLD given a negative test result.

h

E1 is the efficiency or percent of correct classifications made without applying the test. It is equal to 1- Base Rate %.

i

E2 is the efficiency or percent of correct classifications made when the test is used and is the sum of the percent of True Positives and True Negatives.