Syntactic differences between older adults with and without depressive disorders: a pilot study in Thailand

Abstract

Background: Late-life depression is a prevalent mental health condition among older adults, impacting emotional and cognitive functions including language expression. In depression, semantics such as conveying feelings of sadness or hopelessness, are commonly affected, while syntax, involving sentence structure, has received limited attention in the context of late-life depression. This study aims to investigate syntactic differences between older individuals with and without major depressive disorder (MDD). Additionally, we explore the association between syntax ability scores and depression severity, along with differences in cognitive ability scores between the two groups.

Methods: A total of 104 participants aged 60 years and above were recruited for this study. Participants receiving a diagnosis of MDD formed the case group, while those without MDD comprised the control group. All participants demonstrated cognitive intactness as assessed using the Mini Cog test. The final sample consisted of 22 individuals in each group. Demographic information including sex, age, marital status, residence location, income and medical history via questionnaires were collected.

All participants completed the Thai version of the Geriatric Depression Scale (TGDS). Licensed clinical psychologists administered composite tests drawn from the Stanford

Binet Intelligence Scales, Fifth Edition (SB5) and the Wechsler Adult Intelligence Scale, Fourth Edition including the Early Reasoning subtest and the verbal comprehension index (comprising vocabulary, similarities and comprehension). The outcomes included syntax scores and cognitive ability scores. We also recorded reaction times for each test.

Descriptive statistics using frequency, mean and standard deviation for sociodemographic and clinical data were conducted. Student’s t-test was applied to assess group differences in the test scores using the 2000 bootstrapping method. Cohen’s d effect size was provided. Pearson's correlation was used to examine the relationship between syntax scores and depression severity. Significance levels were set at p <0.05. IBM SPSS, Version 22, was used to analyze data.

Results: The mean age of participants was 67.22 (SD 6.32) for the case group and 67.86 (SD 5.21) for the control group, with 59% being female. No significant differences were observed in age, sex, education level, dialect spoken, income level or marital status between the case and control groups. While no disparity was noted regarding Mini-Cog scores, TGDS scores were significantly higher in the case group compared with those in the control group (t (42) = 3.086, p <.01), with a large effect size (Cohen's d = 4.0), indicating that only depressive symptoms, and not cognitive function, differed between the two groups.

Regarding performance on cognitive tests, the case group performed lower across all tests, but only the early reasoning part showed a statistically significant difference between the groups, with a moderate to large effect size (Cohen's d = 0.646-0.785). The case group had a mean score of 1.53 (SD = 0.40) on the early reasoning part, while the control group recorded a mean score of 1.76 (SD 0.28), p <.05. Scores on the other tests including the similarity subtest, vocabulary test and comprehension subtest were lower in the case group but not significantly so (p >.05). In exploring the relationship between depression severity and syntax scores, a significant correlation was observed concerning the early reasoning test (r = -0.426 (bootstrap 95% CI = -0.639, -0.143), p <.01). Furthermore, significant differences in reaction times were noted for some early reasoning subtests.

Conclusion: Participants with depressive disorders demonstrated lower syntactic ability. However, only specific tests showed sensitivity in detecting differences between the two groups. The relatively small sample size may have limited our ability to detect subtle differences in some tests. Nevertheless, these findings could inform future research aimed at develop more effective tools for depression screening among older adults using syntactical analysis.