1. THE PERCENTAGE OF WORDS KNOWN IN A TEXT AND READING COMPREHENSION
Norbert Schmitt
University of Nottingham
Xiangying Jiang
West Virginia University
William Grabe
Northern Arizona University

2. Reading Performance and Vocabulary Knowledge are Strongly Related
(Laufer, 1992)
(Qian, 1999)
(Qian, 2002)

3. The Ability to Read Requires A Large Vocabulary
How Much?
Early Research
3,000 word families (Laufer, 1992)
5,000 individual words (Hirsh and Nation, 1992)
5,000 words Laufer (1989)

4. The Ability to Read Requires A Large Vocabulary
How Much?
Recent Research
8,000-9,000 word families (Hu and Nation 2000; Nation, 2006)
1st 1,000 word families average about 6 members (types per family)
9th 1,000 frequency level average 3 members
SO 8,000 word families = 34,660 individual word forms

5. Why Different Estimates? 3,000 vs 9,000 Word Families
Different criteria of ‘adequate’ comprehension (Laufer – 55%)
Short texts
Small participant numbers (66)
Old frequency counts (Dutch)
Determination of unknown words

6. Vocabulary Coverage
Laufer (1989) found 95% coverage was point which best distinguished ‘comprehenders’ vs. ‘noncomprehenders’
95%  3,000 word families
Hu and Nation (2000) tested comprehension at various coverages
80% = No learners had adequate comprehension
90% = Only a few
95% = %
At 95% coverage, less than half of the students were successful, so required coverage is higher: 98-99%
98-99%  8,000-9,000 word families

7. Vocabulary Coverage
So the vocabulary coverage requirement is critical:
3,000 vs 9,000 word families
This study will directly explore the relationship between vocabulary coverage and reading comprehension

8. Vocabulary Coverage / Reading Comprehension

9. Vocabulary Coverage / Reading Comprehension

10. Vocabulary Coverage / Reading Comprehension

11. Features of Our Study Longer texts (582 and 757 words)
Extensive vocabulary test
Extensive reading comprehension tests
Controlled for background knowledge of texts
664 participants from different L1s

12. Selection of Reading Passages
CLIMATE
MICE
Length
757 words
582 words
Content
Climate change and global warming
A study on the relationship between exercise and mental acuity
Prior knowledge
With much prior knowledge
With little prior knowledge
Difficulty
Flesch-Kincaid Grade Level: 9.8
Flesch-Kincaid Grade Level: 9.7

13. Development of the Vocabulary Test
a checklist format (check the words they know)
120 target words sampled from the texts and 30 nonwords
deleted anybody with over 3 nonwords checked (≥2 nonwords same result)
high sampling rate for a good estimate of how much vocabulary each learner knew in each text

14. Development of the Reading Comprehension Tests
A two-part reading test for each passage
14 multiple-choice items
16 graphic organizer completion items
graphic organizers were created to reflect the major discourse structures of the text
fill in partially-completed graphic organizers

15. Participants L1 # Levels Turkish 292 IEP 135 Chinese 180 Freshman 270
Arabic
101
Sophomore
143
Spanish 33
Junior 43
Hebrew 26
Senior 50
Other lgs 32
Graduate 23
Total
664

16. Procedure 100 minutes for the entire test battery
Biodata survey (5 mins.)
Vocabulary checklist (15 mins.)
Reading the Climate passage and answer comprehension items (40 mins.)
Reading the Mice passage and answer comprehension items (40 mins.)

17. Initial Screening
Eliminated participants who checked more than 3 nonwords
Eliminated participants who attempted less than 5 items in the graphic organizer task for either passage

18. Scoring Vocabulary percentage
automatically calculated by entering checklist selections into an EXCEL spreadsheet
Multiple-choice reading comprehension test
1 point for each correct answer, 0 for incorrect ones
Graphic organizer reading comprehension test
1 point for each acceptable answer and 0 for unacceptable ones
Interrater reliability .99

19. Reliability Estimates of the Reading Test
.82 for the entire reading test
.79 for the Climate reading test
.65 for the Mice reading test
.59 for the multiple-choice items
.81 for the graphic organizer items
Note: based on KR-21, possible underestimation

20. Vocabulary Coverage vs Reading Comprehension

21. The Influence of Background Knowledge

22. Graphic Organizer vs Multiple-Choice Tests

23. Conclusions
The vocabulary coverage / comprehension relationship is essentially linear between 90% - 100% coverage
So coverage requirements depends on comprehension goals
98% coverage is probably necessary, as 70% comprehension is desirable
But even 90% coverage leads to 50% comprehension
100% coverage only lead to 75% comprehension, so successful reading requires more than vocabulary, but high vocabulary levels are clearly a key requirement
Higher background knowledge lead to about 10 percentage-points better comprehension
There is a large amount of variation among learners