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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