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Table 1 Summary of studies using intelligence tests in adults with DS. Tests are arranged into those not specifically designed for children and adolescents and those that are. AB tests not shown (see Table 2). Ages and age-equivalents given in years; where given in months in original papers these have been converted. Ages and scores given as mean (SD; range). NR indicates “not reported”

From: Assessing general cognitive and adaptive abilities in adults with Down syndrome: a systematic review

Study IQ test Score type(s) provided Participants Participant ages Raw scores Standardised scores Floor effects
Tests not specifically designed for children and adolescents (most recent first)
 Lao et al., [26] PPVT-IV Standardised score and age-equivalent score 52 37.3 (6.6; 30–50) NR 56.6 (17.2) standardised score; 8.19 (3.44) age-equivalent score NR
 Hartley et al. [14]* PPVT-IV Age-equivalent score 58 37.6 (6.8; ≥ 30) NR 8.10 (3.34) NR
 Tomaszewski et al. [15] Stanford Binet 5th Ed Full IQ score 31 25.9 (5.92) NR 46.6 (9.1) NR
 Sinai et al. [11] KBIT-2 Raw scores for verbal and non-verbal subscales 30 no dementia 50.9 (4.83) Total, 23.17 (19.50; 3–63);
Verbal, 16.37 (13.33; 1–47);
Non-verbal, 6.8 (6.92; 0–15)
NR Verbal, 0%;
Non-verbal, 16.7%
19 diagnosed or possible dementia 55.6 (6.77) Total, 9.74 (11.06; 1–49);
Verbal, 6.53 (7.16; 0–34);
Non-verbal, 3.21 (4.16; 0–20)
NR Verbal, 5.3%;
Non-verbal, 21.1%
 Startin et al. [16] KBIT-2 Raw scores for verbal and non-verbal subscales; full IQ scores floor effects only 130 aged 36+ years without dementia 47.77 (7.01; 36–71) Verbal, 30.55 (17.47; 2–80);
Non-verbal, 12.55 (6.57; 0–32);
NR Verbal raw, 0%;
Verbal IQ, 66.7%;
Non-verbal raw, 6.7%;
Non-verbal IQ, 39.4%
51 aged 36+ years with dementia 54.20 (6.95; 38–67) Verbal, 18.68 (13.77; 1–51);
Non-verbal, 8.29 (6.45; 0–19)
NR Verbal raw, 0%;
Verbal IQ, 84.0%;
Non-verbal raw, 16.7%;
Non-verbal IQ, 62.5%
124 aged 16–35 years 25.24 (5.53; 16–35) Verbal, 35.03 (16.77; 2–82);
Non-verbal, 14.98 (6.9; 0–32)
NR Verbal raw, 0%;
Verbal IQ, 50.8%;
Non-verbal raw, 4.1%;
Non-verbal IQ, 33.9%
 de Sola et al. [17] KBIT (Spanish version) Full IQ score; combined verbal and non-verbal standardised KBIT score 86 23.3 (4.3; 16–34) NR Full IQ median, 41;
Standardised KBIT score, 105 (17.8; 80–180)
41.9%
 Ghezzo et al. [8] WAIS-R Full IQ score; verbal IQ score; performance IQ score 36 adults with DS (of a larger sample of 67 participants which included children) 18–29 years.: n = 24, 22.34 (3.40)
30–39 years.: n = 17, 34.27 (3.04)
≥ 40: years. n = 18, 49.34 (6.91)
NR Total IQ
18–29 years., 49.71 (12.69)
30–39 years., 48.80 (11.84)
≥ 40, 33.20 (19.60)
Verbal IQ
18–29 years., 53.43 (13.02)
30–39 years., 51.60 (12.91)
≥40, 33.60 (20.02)
Performance IQ
18–29 years., 51.38 (12.49)
30–39 years., 52.90 (12.44)
≥40, 36.20 (23.72)
NR
 Breia et al. [18] WAIS-III (Portuguese version) Full IQ score; verbal IQ score; non-verbal IQ score 26 (of a larger sample of 209) Full sample, 32.6 (8.58) NR Full scale IQ, 49.65 (4.93; 45–61);
Verbal IQ, 52.27 (5.65; 45–64);
Non-verbal IQ, 50.77 (5.06; 45–62)
NR
 Iacono et al. [13] PPVT-III Age-equivalent score 55 38 (19–58) NR 5.17 (2.17; 1.67–9.75) NR
RCPM Raw score 55 38 (19–58) 10.65 (3.95; 4–20) NR NR
 Kay et al. [19] PCFT Raw scores 85 38.2 88.0 (61.9; 0–224)
Median 97
NR NR
 Patel et al. [20] Five subtests from the early-development battery of the WJTCA-R Raw scores 82 females (58 pre-menopausal, 24 post-menopausal), 80 males Total range 21–57; premenopausal females 34.7 (6.8), postmenopausal females 49.7 (4.2) Pre-menopausal females, 468.7 (15.9); age-matched males, 462.2 (17.7)
Post-menopausal females; 446.2 (19.0 SD); age-matched males, 453.1 (23.3 SD)
NR NR
Tests designed for children and adolescents (most recent first)
 de Knegt et al. [21] WPPSI-R Age-equivalent score 244 38.1 (11.1) NR 5.0 (1.5) NR
 d’Ardhuy et al. [10] Leiter-R (full) Non-verbal IQ score 41 22.7 (3.4; 18–30)   39.0 (6.0; 36–65) 61%
 Dressler et al. [22] RCPM** or Leiter-R Age-equivalent score 49 28.8 (8.4; 19–52) NR 4.72 (2.46; 3.06–10.0) NR
 Strydom et al. [23] BPVS-II Raw and age-equivalent score 32 (10 mild ID, 18 moderate ID, 4 severe ID) 32.59 (6.78; 18–45) 67.8 (22.89; 14–112) Mild ID, 7.8;
Moderate ID, 4.7;
Severe ID, 2.04;
Overall range 2.04–12.01
3 individuals could not complete the test
 Glenn and Cunningham [12] BPVS-II Age-equivalent score 46 19.83 (1.92; 16.17–24.33) NR 6.53 (1.98) NR
Leiter-R (brief) Non-verbal IQ; age-equivalent score 46 19.83 (1.92; 16.17–24.33) NR Non-verbal IQ, 3.3 (0.5);
Age-equivalent, 5.2 (1.0)
Majority of IQ scores were 36, with very few over 45, despite age-equivalent scores differing
 Kittler et al. [24]* WISC-R Raw scores 42 (21 females, 21 males) Female, 37.9 (5.9)
Male, 40.3 (5.7)
Verbal subtests:
Information: F 6.6 (3.7), M 7.2 (4.0)
Similarities: F 4.0 (5.3), M 3.2 (4.5)
Arithmetic: F 3.1 (2.0), M 2.7 (1.8)
Vocabulary: F 13.9 (7.2), M 17.3 (9.1)
Comprehension: F 6.7 (4.7), M 7.4 (5.0)
Non-verbal subtests:
Picture completion: F 7.8 (5.3), M 8.6 (4.4)
Picture arrangement: F 4.4 (5.1), M 2.6 (3.6)
Block design: F 9.6 (7.3), M 8.0 (6.0)
Object assembly: F 11.7 (6.1), M 8.7 (5.8)
Coding: F 22.0 (10.5), M 15.7 (9.6)
NR 40% scored 0 or 1 on Picture Arrangement; 48% scored 0 or 1 on Similarities
 Devenny et al. [25]* WISC-R Subtest raw scores 44 46.85 (6.01) Information, 6.64 (3.71);
Arithmetic, 3.00 (2.03);
Vocabulary, 15.59 (7.83);
Comprehension, 7.17 (5.14);
Picture completion, 7.67 (4.69);
Block design, 8.82 (6.90);
Object assembly, 9.68 (6.17);
Coding, 18.33 (10.82);
Digit span, 2.98 (2.25)
NR 52% scored 0 or 1 on Picture Arrangement; 66% scored 0 or 1 on Similarities
 Das et al. [7] PPVT-R** Raw score 16 younger 43.7 (2.9; 40–49) 57.75 (21.16) NR NR
16 older 55.2 (3.9; 50–62) 43.00 (40.98) NR NR
MAT Raw score 16 younger 43.7 (2.9; 40–49) 6.25 (4.67) NR “Too difficult for most participants”
16 older 55.2 (3.9; 50–62) 3.75 (3.51) NR
  1. *Only T1 data used in this review
  2. **Not designed for children and adolescents
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