In my role as an APC assessor, I have found there are many common errors that are made when submitting a report for a submission for APC, when marked against the marking criteria.
The fourth common error is around calculating the composite score for Phonological Memory as part of the CTOPP-2 (ages 7-24). Correct calculation of scores is part of marking criterion 5 where it states:
Information in the report reflects that tests have been administered correctly and all scores are calculated, converted and reported with 100%. accuracy.
I have observed instances where the confidence interval used for Phonological Memory has been 8 (which is the value used for Phonological Awareness, Rapid Symbolic Naming and Alternative Phonological Awareness), but it should be 12. I surmise that people may have overlooked the fact that this one composite score has a different Standard Error of Measurement (SEM) from the others in the Composite Performance section.
There is not such as emphasis on confidence intervals in the new SASC formatting but SASC are very insistent that, even though Confidence Intervals do not need to be used, we need to know how to work them out. As the SASC Additional Guidance explains, confidence intervals may be included to indicate test reliability. However, confidence intervals cannot be used to compare test scores unless tests are co-normed.
Calculating the confidence interval for Phonological Memory: CTOPP 2
- Look at the front of the CTOPP-2 booklet (ages 7-24- blue)
- Find Section 3: Composite Performance
- Look at Phonological Memory and work across until you see SEM.
- You will see a number: SEM 6
- To work out the confidence interval at 95% use the standard formula which is given on page 52 of the CTOPP-2 manual:
95% confidence interval = SEM x 1.96
(and round up or down to nearest whole number).
In other words: 6 x 1.96 = 11.76 which is rounded to 12.
So, the confidence interval for Phonological Memory is +/-12
If your composite standard score is 80 for Phonological Memory (for example), the Confidence Interval will be 68-92.
To avoid the common misconceptions associated with their use, confidence intervals should be explained carefully in Appendix 1 of your report. This helps with accessibility, which is part of marking criterion 15 in the APC Review Proforma.
In this way, you have demonstrated that this confidence interval is calculated correctly, which is part of marking criterion 5 in the APC Review Proforma that all SpLD APC awarding bodies are using when reviewing an APC (The Dyslexia Guild, BDA and PATOSS).