Abstract
Objectives. It has been shown that propositional density (PD), which roughly corresponds to the number of ideas expressed in a text of given length, is related to cognitive performance in the older age.
The present study investigated differences in propositional density in oral language production between healthy seniors and patients with mild cognitive impairment (MCI). MCI is generally accepted as a prodromal stage of Alzheimer's disease (AD).
Sample and setting. The sample included 33 MCI persons and 32 healthy controls (mean age 73 years).
The groups were equivalent as for the age and education. As expected, there was a significant difference between Mini-Mental State Examination (MMSE) scores between the groups, with MMSE being a simplified measure of their cognitive status.
Hypotheses. Lower PD was expected in MCI persons, as the task required recent past recall which is considered one of the early deficiencies in early AD and MCI due to AD.
Statistical analysis. Mean PD across groups was compared using the independent samples t-test.
Results. Mean propositional density in MCI persons was 48,74% (SD 5,78), and in healthy controls 53,06% (SD 4,56).
The difference was statistically significant (p<0,001). Cohen's d 0,83 represents a large effect size for the group difference.
Study limitations. The main limitation is the heterogeneity of the MCI group.
Also, the detailed cognitive status of the healthy controls is unknown. Thus the group could include persons with some cognitive impairment which has not been detected yet.