Questioning the Meaning of a Change on the Alzheimer’s Disease Assessment Scale–Cognitive Subscale (ADAS-Cog): Noncomparable Scores and Item-Specific Effects Over Time

Abstract

Longitudinal invariance indicates that a construct is measured over time in the same way, and this fundamental scale property is a sine qua non to track change over time using ordinary mean comparisons. The Alzheimer’s Disease Assessment Scale–cognitive (ADAS-Cog) and its subscale scores are often used to monitor the progression of Alzheimer’s disease, but longitudinal invariance has not been formally evaluated. A configural invariance model was used to evaluate ADAS-Cog data as a three correlated factors structure for two visits over 6 months, and four visits over 2 years (baseline, 6, 12, and 24 months) among 341 participants with Alzheimer’s disease. We also attempted to model ADAS-Cog subscales individually, and furthermore added item-specific latent variables. Neither the three-correlated factors ADAS-Cog model, nor its subscales viewed unidimensionally, achieved longitudinal configural invariance under a traditional modeling approach. No subscale achieved scalar invariance when considered unidimensional across 6 months or 2 years of assessment. In models accounting for item-specific effects, configural and metric invariance were achieved for language and memory subscales. Although some of the ADAS-Cog individual items were reliable, comparisons of summed ADAS-Cog scores and subscale scores over time may not be meaningful due to a lack of longitudinal invariance.

State, trait, and accumulated features of the Alzheimer's Disease Assessment Scale Cognitive Subscale (ADAS‐Cog) in mild Alzheimer's disease

“…In total, 341 subjects with mild AD who had baseline ADAS‐Cog scores available were included as reported previously. 20 At baseline, participants were, on average, 75 years old (standard deviation [SD] = 5), 55% male, and had 15 years of education (SD = 3). The percentage of apolipoprotein E ε4 carriers was 66%.…”

“…In a mild AD population, a recent study evaluated the ADAS‐Cog for longitudinal invariance, a statistical criterion required before means can be compared from one moment of assessment to the next 20 . Those results raised concerns that the different items might track AD progression differently over time.…”

“…In a mild AD population, a recent study evaluated the ADAS‐Cog for longitudinal invariance, a statistical criterion required before means can be compared from one moment of assessment to the next. 20 Those results raised concerns that the different items might track AD progression differently over time. Although typically the ADAS‐Cog items are summed to arrive at total or subdomain scores, that analysis also suggested that this might be discouraged because the items did not inform an underlying cognitive factor, or underlying subdomain factors (e.g., memory, praxis, language) uniformly from one visit to the next.…”

A Multidomain Intervention Program for Older People with Dementia: A Pilot Study

“…Assessment Scale-Cognitive (ADAS-Cog) 13-item version 47 The 13-item version of the ADAS-Cog is allowed for calculation of the 13-item total score, where a higher score indicates poorer performance and greater impairment. ADAS-Cog 13item version was validated in translation in Vietnam.…”

A Multidomain Intervention Program for Older People With Dementia: a Pilot Study

“…Alzheimer's Disease Assessment Scale-Cognitive (ADAS-Cog) 13item version [40] The 13-item version of the ADAS-Cog is allowed for calculation of the 13-item total score, where a higher score indicates poorer performance and greater impairment Clinical Dementia Rating (CDR) [29] The CDR is a widely utilized clinical tool for grading the relative severity of dementia. The CDR-Sum of Boxes score is obtained by summing each of the domain box scores, with scores ranging from 0 to 18 [41].…”