Table 1 Demographics and descriptive characteristics (N = 491)
|
Variable
|
Mean (SD)†
|
Range
|
Age (years)
|
64.9 (4.2)
|
60 to 86
|
60 to 64 years – n (%)
|
278 (56.6%)
|
|
65 to 69 years – n (%)
|
139 (28.3%)
|
|
70 to 75 years – n (%)
|
61 (12.4%)
|
|
75 years and older – n (%)
|
13 (2.6%)
|
|
Sex – n (%)
|
|
|
Female
|
310 (63.1%)
|
–
|
Education
|
|
|
Total years spent in school and higher education
|
15.0 (3.2)
|
8 to 26
|
Current country of residence – n (%)
|
|
|
United Kingdom
|
287 (58.5%)
|
–
|
United States
|
143 (29.1%)
|
–
|
Canada
|
10 (2.0%)
|
–
|
Ireland
|
3 (0.6%)
|
|
France
|
3 (0.6%)
|
|
Australia
|
2 (0.4%)
|
|
Italy
|
2 (0.4%)
|
|
Greece
|
2 (0.4%)
|
|
Chile
|
2 (0.4%)
|
|
Other (Austria, Estonia, Netherlands, Portugal, Spain, Sweden)
|
6 (1.2%)
|
–
|
Not reported
|
31 (6.3%)
|
|
Subjective cognitive decline assessed continuously
|
|
|
Self-perceived cognitive function (Neuro-QoL)
|
32.7 (5.8)
|
11 to 40
|
Subjective cognitive decline assessed categorically
|
|
|
Memory complaints – n (%)
|
119 (24.2%)
|
–
|
Worried about memory complaints – n (%)
|
79 (16.1%)
|
–
|
Medical professional sought for memory complaints – n (%)
|
16 (3.3%)
|
–
|
Repetitive negative thinking‡ (PTQ)
|
23.6 (10.7)
|
0 to 60
|
Rumination (RRS-10)
|
17.6 (5.3)
|
10 to 36
|
Worry (PSWQ-8)
|
19.5 (8.9)
|
8 to 40
|
Purpose in life (Ryff’s wellbeing subscale)
|
27.8 (6.6)
|
6 to 36
|
Openness to experience (BFI-10)
|
3.75 (0.94)
|
1 to 5
|
Conscientiousness (BFI-10)
|
3.95 (0.91)
|
1 to 5
|
Extraversion (BFI-10)
|
3.00 (1.15)
|
1 to 5
|
Agreeableness (BFI-10)
|
3.67 (0.85)
|
1 to 5
|
Neuroticism (BFI-10)
|
2.59 (1.12)
|
1 to 5
|
Regular meditation practice – n (%)
|
43 (8.8%)
|
–
|
Meditation experience (years)
|
13.2 (14.6)
|
1 month to 50 years
|
Abbreviations: SD, standard deviation; PTQ, Perseverative Thinking Questionnaire; RRS-10, 10-item Rumination Response Scale; PSWQ-8, 8-item Penn State Worry Questionnaire; BFI-10, 10-item Big Five Inventory.
†All statistics are mean (SD) unless otherwise specified.
‡n=490
|
Measures
Participants were asked to indicate demographic details (i.e., age, sex, education, country of residence).
SCD was assessed continuously via a measure of self-perceived cognitive function, namely, the Cognition Function– Short Form from the Neuro-QoL Item Bank v2.0 (40). This 8-item measure assesses memory, attention, and reasoning difficulties using a 5-point Likert scale ranging from 1 (very often/cannot do) to 5 (never/none). Four items ask about the past 7 days (e.g., “I had to read something several times to understand it”); and four items ask about how much difficulty participants currently have performing certain activities (e.g., “Planning for and keeping appointments that are not part of your weekly routine”). Total scale scores are computed by summing all item scores with higher scores reflecting higher levels of self-perceived cognitive function. The Neuro-Qol Item Bank v2.0 has displayed adequate psychometric properties (40). In the present study, Cronbach’s alpha for the 8-item Cognition Function– Short Form was 0.90.
SCD was assessed categorically via questions about memory complaints because an impaired memory is the most frequently reported complaint in research on SCD (e.g., 1, 41, 42) and because previous cross-sectional research has utilised similar approaches to classifying SCD (e.g., 43, 44). Participants answered the following question: “Do you have memory complaints?”. If participants reported memory complaints, they were asked “Do these complaints worry you?”. If they reported being worried, they were also asked “Have you seen a medical professional for your memory complaints?". In the context of this study, participants with memory complaints were classified as having SCD. In other words, the answer to the question “Do you have memory complaints?” was used as a binary outcome variable capturing SCD.
To measure RNT, the Perseverative Thinking Questionnaire (PTQ) was used (45). The 15-item self-report measure uses a 5-point Likert scale ranging from 0 (never) to 4 (almost always) to capture how participants typically think about negative experiences or problems. Although RNT comprises both worry and rumination, the PTQ items are time-independent. Specifically, they do not specify whether negative thoughts are related to the past or the future. Total PTQ scores are the sum of all item scores. Higher scores reflect higher levels of repetitive negative thinking (possible range: 0 to 60). The PTQ has displayed good internal consistency and reliable factor structure across samples (45). Cronbach’s alpha in the present study was 0.95.
Worry and rumination, aspects of RNT, were measured using the 8-item Penn State Worry Questionnaire (46) and the 10-item Rumination Response Scale (47), respectively. Both measures were included to assess aspects of future- versus past-directed negative thoughts that are not directly captured by the content-independent measure of RNT (i.e., the PTQ). The 8-item Penn State Worry Questionnaire uses a 5-point Likert scale ranging from 1 (not at all typical of me) to 5 (very typical of me). The 10-item Rumination Response Scale uses a 4-point Likert scale ranging from 1 (almost never) to 4 (almost always). Total worry and rumination scores are derived by summing all the respective item scores with higher scores indicating higher levels of worry and rumination, respectively. Both scales have displayed adequate psychometric properties (46, 47). In the present study, Cronbach’s alpha for the 8-item Penn State Worry Questionnaire and the 10-item Rumination Response Scale was 0.96 and 0.84, respectively.
To measure purpose in life, the 6-item purpose in life subscale of the Well-being Scale was used (48), which has been used in previous research involving older adults (33). This measure uses a 6-point Likert scale ranging from 1 (strongly disagree) to 6 (strongly agree) to capture levels of purpose in life. Total purpose in life scores are derived by summing all item scores, with higher scores indicative of higher levels of purpose in life (possible range: 6 to 36). The purpose in life subscale has displayed good psychometric properties (45). In the present study, Cronbach’s alpha was 0.90.
To measure personality traits, the 10-item short version of the Big Five Inventory was used (49). This measure uses a 5-point Likert scale ranging from 1 (disagree strongly) to 5 (agree strongly) to capture the personality traits of openness to experience, conscientiousness, extraversion, agreeableness, and neuroticism (32). Each personality trait is captured by two items and total scores for each trait are computed by averaging the respective items scores. Higher subscale scores relate to higher levels of the respective trait. Using expert judgment and empirical item analyses, the abbreviated 10-item version was developed based on the standard 44-item Big Five Inventory (50). Despite being substantially shorter, the 10-item version of the Big Five inventory has retained significant levels of reliability and validity and was recommended for the use in time-constrained research settings (46).
Participants reported whether they “practice meditation regularly (on average at least 2-3 times per week)” without including activities such as yoga, tai chi, qigong, and prayer. Those with a regular meditation practice were further asked to indicate for how long they have been regularly practicing meditation.
Statistical analysis
We built the statistical models within a risk prediction framework. We developed a set of linear and logistic regression models with self-perceived cognitive function (i.e., SCD assessed continuously) and endorsement (yes/no) of memory complaints (i.e., SCD assessed categorically) as the continuous and binary outcome variable, respectively. We used a stepwise backwards elimination approach in which explanatory variables (i.e., all psychological risk/protective factors described above) were retained if they were associated with p < 0.01. This conservative threshold for inclusion was chosen to ensure model stability and reduce overfitting.
To that end, we first fitted univariable linear regression models to assess the unadjusted association between self-perceived cognitive function and all psychological risk/protective factors; and we fitted univariable logistic regression models to assess the unadjusted association between memory complaints (yes/no) and all psychological risk/protective factors. Second, we fitted multivariable linear and logistic regression models that included all explanatory variables that were associated with p < 0.01 in the univariable regression models. The final prediction models retained all explanatory variables that were associated with p < 0.01 in the multivariable models. Age, sex, and education were retained in all models based on their established association with cognitive decline and dementia. Sensitivity logistic regression analyses were conducted that only included participants who reported worries about their memory complaints (yes/no) because worries about memory complaints have been identified as a high-risk feature of the SCD-plus classification (1). All analyses were conducted using Stata 13.0 (51).
Given the absence of previous studies on the relationship between RNT and self-perceived cognitive function or memory complaints in older adults at the time of data collection, no effect size estimates were available on which to base a formal power analysis for sample size determination. Given the novelty of this research question, we considered a large sample size of at least 450 participants to be a conservative estimate for informing hypothesis-generation in the context future of longitudinal studies.