Background: In developing the PB-50 word lists, J. P. Egan suggested five developmental principles,
two of which were “equal average difficulty” and an “equal range of difficulty” among
the lists (page 963). Egan was satisfied that each of the 20 PB-50 lists had equivalent
ranges of recognition performances and that the lists produced the same average performances.
This was accomplished in preliminary studies that measured the recognition performance
of each word and eliminated words that were always or never correct. In preparing
for studies of interrupted words, we needed to know the range of difficulty inherent
in the speaker specific NU-6 and Maryland CNC materials we planned to use when those
words were not interrupted. There were only a few studies in the literature that touched
on the range of difficulty characteristic of the word-recognition materials in common
usage. The paucity of this information prompted this investigation whose scope broadened
to include the CID W-22, Maryland CNC, NU-6, and PB-50 materials spoken by a variety
of speakers.
Purpose: The purpose was to evaluate the homogeneity with respect to intelligibility of the
words that comprise several of the common word-recognition materials used in audiologic
evaluations.
Research Design: Both retrospective (10) and prospective (3) studies were involved. Data from six
of the retrospective studies were from our labs. The prospective studies involved
both listeners with normal hearing for pure tones and listeners with sensorineural
hearing loss.
Study Sample: The sample sizes for the 13 data sets ranged from 24 to 1,030, with 24 the typical
number for listeners with normal hearing.
Data Collection and Analysis: The retrospective data were from published studies and archived data from our laboratories.
The prospective studies involved presentation of the word-recognition materials to
the listeners at a comfortable level. An item analysis was conducted on each data
set with descriptive statistics used to characterize the data. Additionally, skewness
coefficients were calculated on the distributions of word performances and the interquartile
range was used to determine minor and major outliers within each set of 200 words
and their component 50-word lists (300 words for the Maryland CNCs).
Results: For listeners with normal hearing the majority of performances on the words within
a 50-word list were better than the mean performance, which produced negatively skewed
distributions with outlier performances in every list. For listeners with sensorineural
hearing loss the performances on the words within a 50-word list were evenly distributed
above and below the mean performance, which yielded essentially normal distributions
with few outliers. There were a few words on which performances were better by the
listeners with hearing loss.
Conclusions: Every list of word-recognition materials has a few words on which recognition performances
are noticeably poorer than performances on the majority of the remaining words. If
the intention of an experiment is to evaluate performance at the word level, then
identifying these “outliers” becomes a necessity. Although not evaluated in this report,
the implications for 25-word lists are they should be based on recognition-performance
data and not compiled arbitrarily.
Key Words
Auditory perception - hearing loss - homogeneity - speech - speech perception - word
recognition
