Informant Questionnaire on Cognitive Decline in the Elderly

Transient Ischemic Attack (TIA)/Stroke: (van Nieuwkerk et al., 2021; n = 1068; mean age = 72.9 (12.3), male = 52.3%; 16-item IQCODE)

• The optimal cut-off score of IQCODE for assessing prestroke dementia was > 3.48 (sensitivity 89.7%, specificity 84.2%).
  • Optimal cut-off score was nonsignificantly higher for major stroke (NIH Stroke Scale score >= 3) than minor stroke (> 3.85 vs. > 3.47), but was similar for patients with first-ever stroke (> 3.48; sensitivity 85.7%, specificity 84.8%).

Acute Stroke: (Tang et al., 2003; n = 189; mean age = 74.2 (10.4) years; female = 52.9%; mean National Institute of Health Stroke Scale score = 11.9 (10.6); time since stroke 14.3 (1.4) weeks; Chinese sample and translation of 26-item IQCODE).

• The optimal cut-off point of the IQCODE for assessing post-stroke dementia was ≤ 3.40 (sensitivity 88%; specificity 75%) 

Acute Stroke: (Hénon, Pasquier, Durieu, Godefroy, Lucas, Lebert, Leys, 1997; n = 202, median age = 75 years; age range = 42-101; female = 52.0%; French sample and translation of 26-item IQCODE).

• Dementia cut-off IQCODE score >= 104

Transient Ischemic Attack (TIA)/Stroke: (van Nieuwkerk et al., 2021)

• Mean item score for all IQCODES = 3.23 (0.55) with median (IQR) = 3.13 (3.00 – 3.38)
  • Mean item score for participants identified with pre-event dementia was 4.34 (0.59) vs. 3.15 (0.46) for those with no dementia (p < 0.0001)

Acute Stroke: (Tang et al., 2003; n = 189).

• Excellent: Cronbach's alpha = 0.95*

Post-Stroke: (Othman et al., 2015; n = 50, mean age = 42.7 (11.6) years, age range = 21-68 years, female = 64%, caregivers of elderly (age > 60) post-stroke outpatients, Malay sample and translation of 16-item IQCODE).

• Excellent:  Cronbach’s alpha = 0.94*

*Scores higher than 0.9 may indicate redundancy in the scale questions.

Predictive validity:

Transient Ischemic Attack (TIA)/Stroke: (van Nieuwkerk et al., 2021)

• Excellent predictive ability of IQCODE for detecting pre-event dementia (AUC = 0.94, 95% C.I. 0.90-0.97, p < 0.001)
  • Significant differences among all 16 IQCODE items for patients with vs. without pre-event dementia, both overall and after stratification for event severity (p < 0.001)

Acute Stroke: (Tang et al., 2003; n = 189).

• Adequate predictive validity (AUC = .88)
• Low positive predictive value (33%) for detecting post-stroke dementia

“The content validity was acceptable as judged by the content experts involved.” (Othman et al., 2015, p. 261) 

After checking the ease of understanding and interpretation of all items, face validity was judged as satisfactory. (Othman et al., 2015, p. 261) 

Alzheimer’s Disease: (Ding et al., 2018; n = 394; mean age = 70.01 (9.77) years; age range = 43-91 years; female = 53.2%; 16-item IQCODE).

• Cut-off between mild to moderate dementia: 65 (sensitivity 66.1%, specificity 59.8%)
• Cut-off between moderate to severe dementia: 75 (sensitivity 73.9%, specificity 67.7%)  

Progressive Dementia: (Perroco, et al., 2008; n = 49; mean age = 70.5 years; female = 49%; 9 classified as Clinical Dementia Rating (CDR) of 0, 11 as CDR = 0.5, and 29 as CDR >= 1; Brazilian sample and translation of 16-item IQCODE).

• Cut-off score between participants with mild cognitive impairment and dementia: 4.0 – 4.1

Progressive Dementia: (Perroco, et al., 2008; n = 49; Brazilian sample and translation of 16-item IQCODE).

Mean scores on the 16-item IQCODE according to Clinical Dementia Rating (CDR) classification

n

CDR

IQCODE

Mean (SD)

10

0

3.37 (0.90)

11

0.5

3.75 (0.42)

17

1

4.32 (0.39) 

9

2

4.61 (0.33)

2

3

5.00 (--)

Alzheimer’s Disease: (Ding et al., 2018; n  = 394).

• Excellent inter-rater reliability (k = 0.894, p < 0.001).

Convergent validity:

Alzheimer’s Disease: (Ding et al., 2018; n = 394).

• Poor area under the curve (AUC) for the IQCODE discriminating between mild and moderate dementia (AUC = 0.666, 95% CI: 0.601-0.732)
• Adequate area under the curve (AUC) for the IQCODE discriminating between moderate and severe dementia (AUC = 0.768, 95% CI: 0.715–0.822)
• Adequate convergent validity between IQCODE scores and neuropsychological measures for those with moderate dementia (CDR = 2) and for all dementia groups:
  • Mini-Mental State Exam (MMSE) (r = -0.409 for moderate, -0.528 for all)
  • Mattis Dementia Rating Scale (r = -0.324 for moderate, -0.436 for all)
  • Alzheimer’s Disease Assessment Scale – Cognitive subscale (r = -0.370 for moderate, -0.477 for all)
  • The above findings suggest that IQCODE is more accurate for assessing moderate dementia than for assessing mild or severe dementia (p. 149).

Progressive Dementia: (Perroco et al., 2008; n = 49).

• Excellent convergent validity between IQCODE-S scores and Clinical Dementia Rating (r = 0.65, p < 0.001)
• Excellent convergent validity between IQCODE-S scores and Clinical Dementia Rating controlled by age and education (r = 0.61, p < 0.001)

Discriminant validity:

Progressive Dementia: (Perroco et al., 2008; n = 49).

• Adequate discriminant validity between IQCODE-S scores and years of schooling (r = -0.33, p = 0.021).

Alzheimer’s Disease: (Ding et al., 2018; n = 394).

• Dementia of different severities had significantly different IQCODE scores for items, except the third item
• The total scores from the mild, moderate and severe groups were 63.38 (±9.49), 68.39 (±8.73) and 75.96 (±3.52), and the differences were significant (p < 0.01).

Older Adults: (Jansen et al., 2008; n = 4823; female = 50.5%; mean age = 76 (6.6) years; Netherlands sample; Dutch language translation of self-report 16-item IQCODE-SR).

• Cut-off score for dementia screening = 3.6

Older Adults: (Phung et al., 2015; n = 236; age = 65 years or older and their informants; Arabic-speaking sample and translation of 16-item IQCODE).

• Cut-off score = 3.34 (sensitivity 92.5, specificity 94.4)

Elderly: (Lourenço & Sanchez, 2014; n  = 417; female = 71.9%; mean age = 79.3 (7.3) years; Brazilian sample and translation of IQCODE into IQCODE-BR)

• Cut-off score = 3.26 (sensitivity 89%, specificity 72%) 

Elderly: (Foroughan et al., 2019; n = 95; age = 60 or greater; Iranian sample; Farsi translation of 16-item IQCODE).

• Acceptable test-retest reliability: (ICC = 0.81)

Elderly: (Jorm & Jacomb, 1989; n = 309 informants who were current caregivers; mean age of subjects = 74 (8.0), female = 61%; 26-item IQCODE)

• Adequate test-retest reliability: (ICC = 0.75) 

Older Adults: (Jansen et al., 2008; n = 4823).

• Excellent: Cronbach’s alpha = .94
• Range of Item-total correlations: r = 0.62 – 0.72
• Range of item-item correlations: r = 0.36 – 0.71 

Older Adults: (Phung et al., 2015; n = 236).

• Excellent:  Cronbach’s alpha = .97

Elderly: (Foroughan et al., 2019; n = 95).

• Excellent: Cronbach’s alpha = .93

Elderly: (Jorm & Jacomb, 1989; n = 613 informants from general population)

• Excellent Internal consistency: Cronbach’s alpha = .95

Concurrent validity:

Elderly: (Jorm et al., 1989; n = 362 informants who were current caregivers; mean age of subjects = 74 (8.0), female = 61%; 26-item IQCODE).

• Excellent concurrent validity between IQCODE and the Mini-Mental State Examination (MMSE) (r  = 0.78).

Elderly: (Isella, Villa, Frattola, & Appollonio, 2002; n = 45; female = 45%; mean age = 67.7(4.9) years; Italian sample and translation of 26-item IQCODE).

• Good concurrent validity between IQCODE and MMSE (0.71).

Predictive validity:

Elderly: (Lourenço & Sanchez, 2014; n = 417).

• Adequate  predictive validity: AUC = 0.88 (95% CI: 0.837-0.917)

Older Adults: (Phung et al., 2015; n = 236).

• Excellent  predictive validity: AUC = 0.96 (95% CI: 0.94-0.99).

Older Adults: (Khobragade et al., 2024; n = 4028, mean age = 69.710 years, age range = 60 – 105, female = 53.8%; informants close family members or friends age 18 years or older; Hindi language used for assessments in 7 states – for the remaining states the assessments were translated into 11 different regional languages and back-translated into English; and 10 participants were assessed in English, for a total of 13 languages; 16-item IQCODE)

• A strong negative association between the full IQCODE and the Hindi Mental State Examination (HMSE): each 1-point increase in IQCODE score was associated with a 3.03-point lower score on the HMSE after controlling for age, gender, and urbanicity.
  • Significant interaction in the association between IQCODE score and HMSE with urbanicity (interaction coefficient = 0.57, p = 0.04): a 1-point difference in IQCODE score was associated with a 3.41-point difference in HMSE score among respondents in urban settings, but a 2.84-point difference in HMSE score among respondents in rural settings.
• Removal of items with high proportions of missing values -- that may be a sign of cultural irrelevance – did not affect criterion validity.
• All criterion validity findings using the HMSE were replicated using the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) Word List Memory Test, an alternative objective measure of cognition. 

Convergent validity:

Elderly: (Lourenço & Sanchez, 2014; n = 417).

• Adequate convergent validity between IQCODE and Cambridge Cognitive Examination score (r = - .46)
• Adequate convergent validity between IQCODE and MMSE score (r = -.58)
• Adequate convergent validity between IQCODE and Instrumental Activity of Daily Living score (r = -.32)
• Adequate  convergent validity between IQCODE and Functional Activities Questionnaire scores (r = 0.59)

Older Adults: (Jansen et al., 2008; n = 4823).

• Adequate convergent validity between IQCODE and instrumental activities of daily living (IADL) (r = 0.34)
• Poor convergent validity between IQCODE and activities of daily living (ADL) (r = 0.27)

Elderly: (Foroughan et al., 2019; n = 95).

• Excellent convergent validity between IQCODE and MMSE (r = -0.647, p < 0.01)
• Excellent convergent validity between IQCODE and Abbreviated Mental Test score (r = -0.641, p < 0.01) 

Elderly: (Foroughan et al., 2019; n = 95).

• To evaluate the content validity and appropriateness of the Farsi version of the IQCODE, an expert panel of seven persons -- three linguists, two psychiatrists, a psychometrist, and a neuropsychologist -- supervised all the steps of translation and adaption of the test, first individually and then in group meetings.
• The finalized version all panel members agreed upon was used for the fieldwork.

Older Adults: (Phung et al., 2015; n = 236).

• IQCODE could effectively discriminate between normal cognition, mild dementia, and moderate dementia (p < 0.0005). 

Elderly: (Lourenço & Sanchez, 2014; n = 417).

• Multivariate analysis showed that there was no statistically significant association between the IQCODE-BR scores and the informants’ mental state, presence of depressive symptoms, as well as living in the same household and being the primary caregiver.
• IQCODE was accurate in assessing the cognitive ability of elderly participants, comparing present and past cognition and functionality

Systemic Lupus Erythematosus (SLE): (Chalhoub & Luggen, 2019; SLE patients fulfilling the updated 1997 American College of Rheumatology Classification Criteria; n  = 78, mean age = 45.9 (11.2); female = 91%; mean disease duration = 10.4 (6.9) years; 16-item IQCODE)

• At the standard cutoff score of >= 3.2 to indicate greater cognitive decline, 26% were identified by the IQCODE as being impaired
• >= 3.1 was the best cutoff for normal controls across all definitions of cognitive dysfunction (CD) from CD1 to CD4 (sensitivity 53%, specificity 52%)
• >= 3.1 was also the best cutoff for rheumatoid arthritis patients (sensitivity 32%, specificity 47%) for CD1 only (number of patients meeting the criteria for CD2, CD3, and CD4 were too low to make reliable assessments. 

Systemic Lupus Erythematosus (SLE): (Chalhoub & Luggen, 2019)

• Poor concurrent validity between total throughput score (TTS) of the Automated Neuropsychologic Assessment Metrics (ANAM) and IQCODE scores (r = -0.034, p = 0.8152)
• No Significant correlations were found between IQCODE scores and any of the individual ANAM subtests. 

Down Syndrome (DS): (Mattar, et al., 2022; n = 92, mean age = 42.43 (8.48) years, age range = 30 – 64), female = 34 (36.9%); inclusion criteria = diagnosed with DS according to ICD-10, code Q90; age >= 30, in daily contact with informant for at least 10 years; diagnostic assessment of dementia made using Cambridge Examination for Mental Disorders of Older People with Down’s Syndrome and Others with Intellectual Disabilities (CAMDEX-DS), with classification into stable condition (n  = 62), mild cognitive impairment (prodromal dementia) (n = 17), and AD (dementia) (n = 13); Portuguese translation of 26-item IQCODE)

• >= 3.14 was the optimal cutoff score for dementia vs. stable condition (sensitivity 100%, specificity 96.8%)
• >=3.11 was the optimal cutoff score for prodromal dementia + dementia vs. stable condition (sensitivity 93.3%, specificity 91.9%)

Predictive validity:

Down Syndrome (DS): (Mattar, et al., 2022; n = 92; Portuguese translation of 26-item IQCODE)

• Excellent predictive ability of IQCODE for dementia vs. stable condition (AUC = 0.993, p < 0.001)
• Excellent predictive ability of IQCODE for prodromal dementia + dementia vs. stable condition (AUC = 0.975, p < 0.001)

Concurrent validity:

Down Syndrome (DS): (Mattar, et al., 2022; n = 92; Portuguese translation of 26-item IQCODE)

• Adequate correlation of IQCODE Score with Cambridge Cognitive Examination adapted for individuals with DS (CAMCOG-DS) total score and domains:
  • Total score (r = -0.333, p = 0.002)
  • Memory domain (r = -0.374, p < 0.001)
  • Attention domain (r = -0.302, p = 0.005)
  • Perception domain (r = -0.338, p = 0.001)
• Poor correlation of IQCODE Score with Cambridge Cognitive Examination adapted for individuals with DS (CAMCOG-DS) domains:
  • Orientation domain (r = -0.214, p = 0.048)
  • Language domain (r = -0.297, p = 0.006)
  • Praxis domain (r = -0.295, p = 0.006)
  • Abstract thinking domain (r = -0.104, p = 0.341)