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. 2018 May 14:10:372-381.
doi: 10.1016/j.dadm.2018.04.003. eCollection 2018.

Underdiagnosis of mild cognitive impairment: A consequence of ignoring practice effects

Jeremy A Elman  1   2 , Amy J Jak  1   3 , Matthew S Panizzon  1   2 , Xin M Tu  4 , Tian Chen  5 , Chandra A Reynolds  6 , Daniel E Gustavson  1   2 , Carol E Franz  1   2 , Sean N Hatton  1   2 , Kristen C Jacobson  7 , Rosemary Toomey  8 , Ruth McKenzie  8 , Hong Xian  9   10 , Michael J Lyons  8 , William S Kremen  1   2
Affiliations

Underdiagnosis of mild cognitive impairment: A consequence of ignoring practice effects

Jeremy A Elman et al. Alzheimers Dement (Amst). .

Abstract

Introduction: Longitudinal testing is necessary to accurately measure cognitive change. However, repeated testing is susceptible to practice effects, which may obscure true cognitive decline and delay detection of mild cognitive impairment (MCI).

Methods: We retested 995 late-middle-aged men in a ∼6-year follow-up of the Vietnam Era Twin Study of Aging. In addition, 170 age-matched replacements were tested for the first time at study wave 2. Group differences were used to calculate practice effects after controlling for attrition effects. MCI diagnoses were generated from practice-adjusted scores.

Results: There were significant practice effects on most cognitive domains. Conversion to MCI doubled after correcting for practice effects, from 4.5% to 9%. Importantly, practice effects were present although there were declines in uncorrected scores.

Discussion: Accounting for practice effects is critical to early detection of MCI. Declines, when lower than expected, can still indicate practice effects. Replacement participants are needed for accurately assessing disease progression.

Keywords: Cognitive change; Longitudinal testing; Mild cognitive impairment; Practice effects; Repeat testing; Serial testing.

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Figures

Fig. 1
Fig. 1
Practice effects by cognitive domain. Practice effects are presented in standard deviation (SD) units for each cognitive ability composite. Bars represent practice effects calculated from unadjusted scores, scores adjusted for education, and scores adjusted for age 20 AFQT. Asterisks indicate significant practice effects (P < .05) as determined by permutation testing. Unadjusted practice effects are likely to be biased upward due to significant group differences in age 20 AFQT and education, thus adjusted scores reflect more accurate estimates. Abbreviation: AFQT, Armed Forces Qualification Test.
Fig. 2
Fig. 2
Impact of practice effect adjustment on diagnosis of MCI. (A) Rate of MCI at each time point before and after correction for PEs. (B) Rates of change in MCI from wave 1 to wave 2 before and after correction for PEs. Abbreviations: MCI, mild cognitive impairment; PE, practice effect.
Fig. 3
Fig. 3
Impact of PEs on individual episodic memory tests. Individual test score composites of the Episodic Memory ability at wave 1 and wave 2. Before correcting for PEs, the scores on the CVLT showed little change, scores on Logical Memory went down, and scores on Visual Reproduction went up. After PE adjustment, all tests showed decreases at wave 2. *Indicates significant (P < .001) difference compared to wave 1 score. Abbreviations: CVLT, California Verbal Learning Test; PE, practice effect.
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