Background
Systematic review methods
Search strategy and selection criteria: IQ tests
Search strategy and selection criteria: AB scales
IQ and general ability tests in people with DS
Tests
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 |
Participant samples
Floor effects
Comparison between IQ test scores
Age-equivalent scores
Standardised test scores
Raw test scores
AB scales in people with DS
Tests
Study | AB scale | Score type(s) provided | Participants | Participant ages | Raw scores | Standardised scores | Floor effects |
---|---|---|---|---|---|---|---|
Gilmore et al., [28] | Vineland ABS 2nd Edition (VABS-II) | Adaptive Behavior Composite score | 21 | 24.83 (1.20) | NR | 51.86 (15.29) | NR |
Hartley et al. [14]* | Vineland ABS 2nd Edition (VABS-II) | Adaptive Behavior Composite score | 58 | 37.6 (6.8; ≥ 30) | NR | 183.67 (47.65) | NR |
Tomaszewski et al., [15] | Vineland ABS 2nd Edition (VABS-II) | Adaptive Behavior Composite score and three individual subscale scores | 31 | 25.9 (5.92) | NR | 52.6 (15.8) (Adaptive Behavior Composite); 45.7 (22.2) (Communication Standard Score); 55.5 (14.4) (Daily Living Skills Standard Score); 64.6 (13.7) (Socialisation Standard Score) | NR |
Dressler et al. [22] | Vineland ABS (Italian version) | Age equivalent scores | 49 | 28.8 (8.4; 19–52) | NR | Total, 7.26 (3.35; 3.06–10.0); Communication sub-domain, 7.18 (3.51); Daily living skills sub-domain, 7.36 (2.62); Socialisation sub-domain, 7.62 (4.32) | NR |
Ghezzo et al. [8] | Vineland ABS | 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) | The following scales (including subscales) for each of the three adult age groups: Communication, Daily living skills, Socialisation, Motor skills. See paper for details. | |||
Kishnani et al., [29]** | Vineland ABS | “Composite Supplemental Norm Score” | 53 (donepezil group); 59 (placebo group) | 24.2 (5.1; 18–36) (donepezil group); 26.0 (5.5; 18–38) (placebo group) | NR | 57.4 (10–99) (donepezil group at baseline); 64.1 (30–99) (placebo group at baseline) | NR |
Witts and Elders [30] | Vineland ABS | Age equivalent scores | 33 | 36 (8.9; 22–53) | NR | 8.5 (3.7; 3.67–18.5) | NR |
Kay et al. [19] | ABS | Raw scores | 85 | 38.2 | 157.5 (59.8; 34–270) Median, 165 | NR | NR |
de Sola et al. [17] | ABAS-II | Raw scores | 86 | 23.3 (4.3; 16–34) | Total, 635.9 (90.9; 220–627); Communication sub-domain, 80.3 (12.7); Community Use sub-domain, 61.5 (13.2); Functional Academics sub-domain, 67.4 (17.9); Home Living sub-domain, 64.3 (12.1); Health and Safety sub-domain, 57.8 (9.5); Leisure sub-domain, 68.2 (11.5); Self-care sub-domain, 87.5 (8.3); Self-direction sub-domain, 73.5 (14.7); Social Skills sub-domain, 75.3 (14.7) | NR | No subscales showed floor effects |
Strydom et al. [23] | ABAS | Raw scores | 32 | 32.59 (6.78; 18–45) | 377 (139.53; 98–589) | NR | NR |
Startin et al. [16] | Short-ABS | Raw scores | 130 aged 36+ years without dementia | 47.77 (7.01; 36–71) | Total, 71.89 (23.39; 14–111); SABS P, 26.74 (6.07; 0–33); SABS C, 24.57 (12.06; 0–47); SABS PS, 20.78 (6.97; 3–32) | NR | Total, 0%; SABS P, 0.9%; SABS C, 0.9%; SABS PS, 0% |
51 aged 36+ years with dementia | 54.20 (6.95; 38–67) | Total, 42.23 (24.51; 3–92); SABS P, 17.02 (9.70; 0–33); SABS C, 10.00 (15.00; 0–31); SABS PS, 13.00 (11.00; 1–28) | NR | Total, 0%; SABS P, 2.3%; SABS C, 2.3%; SABS PS, 0% | |||
124 aged 16–35 years | 25.24 (5.53; 16–35) | Total, 79.03 (19.73; 28–112); SABS P, 28.91 (4.55; 14–33); SABS C, 27.74 (10.36; 4–47); SABS PS, 22.53 (6.49; 7–32) | NR | Total, 0%; SABS P, 0%; SABS C, 0%; SABS PS, 0% |
Floor effects
Comparisons between AB scales
Comparisons between IQ tests and AB scales
Discussion
Conclusions
Recommendations for individual studies of adults with DS | |
1. The use of raw scores for certain IQ tests, particularly the K-BIT2, can minimise floor effects and may therefore be particularly useful in longitudinal studies to track change in cognitive ability over time. | |
2. Non-verbal/performance IQ tests may be useful in multi-site international studies involving populations speaking different languages. | |
3. The use of more common IQ tests (e.g. KBIT, BPVS, WISC-R, RCPM) and AB tests (e.g. VABS, VABS-II, ABS, ABAS) should be encouraged more broadly in both research and clinical settings. Practical implications of this are extremely valuable for detecting changes in ability. | |
4. Studies may benefit from the use of both IQ and AB scales, particularly if participants include individuals with a broad range of abilities. | |
Recommendations for the DS research community | |
1. The development of reporting standards would increase the ability of different study findings to be compared, for example reporting both raw and standardised scores, full floor effects, and separately reported results for individual DS subpopulations. | |
2. Sharing of data from published studies would allow comprehensive comparison between different IQ tests and between different AB tests, in addition to correlations between these two measures for different DS subpopulations. |