Influence of State Anxiety on the Relationship Between Sleep Disturbances and Depressive Symptomology

...

from Monash University, participants were made aware that voluntary completion of the questionnaires provided implied consent. All data collected was anonymous and confidential and access to free counselling service following participation was provided.

Participants were asked to voluntarily complete two online questionnaires, DASS-21 and PSQI in their own time over a two-week period. In the PSQI, participants were asked to answer questions relating to usual sleep habits over the past 30 days. In the DASS-21 participants were required to answer 21 questions using a 4-point frequency scale to rate the extent to which they have experienced each given state over the past week. The data from both questionnaires was collated and incomplete responses were removed from the data set.

Design

This study used a non-experimental design to determine whether there was a correlation between sleep disturbances and depression and anxiety symptomology and whether a relationship still exists between sleep disturbance and depression when anxiety is controlled for. Anxiety and depression were operationalized as scores on the DASS-21 anxiety and depression subscales respectively. Sleep disturbances were operationalized as a score from the PSQI, with a score greater than five indicating ‘poor sleep’.

Data Analysis

A one-tailed Pearson’s correlation was used to assess the relationship between depression and sleep quality. A partial correlation was used to assess whether this relationship was still significant after controlling for anxiety. An alpha level of .01 was used for all statistical analyses.

Results

Descriptive statistics were used to determine the population demographics and variability in the sample.

Table 1

Descriptive statistics for sleep, PSQI and DASS-21 subscales

Measurement Minimum Maximum Mean Std. Deviation

Hours of sleep 4.00 10.50 7.30 1.17

PSQI 3.00 15.00 6.88 2.12

DASS-Depression .00 19.00 3.94 4.04

DASS-Anxiety .00 17.00 3.08 3.06

Age 19 60 24.18 7.70

N = 321

Frequency tables were calculated for PSQI scores to determine the proportion of ‘good’ and ‘poor’ sleepers. As seen in table 1, the majority of participants fell into the category of ‘poor’ sleepers, with a PSQI score >5. In order to then show if there was an existing relationship between depression and sleep disturbances, a one-way Pearson correlation was conducted using an alpha level of .01 to show a positive significant relationship between scores for the PSQI and DASS-21 depression subscale (r(319)= .342, p<.001, one-tailed). Subsequently a partial correlation was conducted between the PSQI and DASS-21 depression scores and remained significant when controlling for anxiety (r(318) = .243, p<.001, one-tailed). SPSS version 20 was used to analyze the data and calculate the descriptive and inferential statistics relevant to this study.

Table 2

Pittsburgh Sleep Quality Index

Frequency Percent Valid Percent Cumulative Percent

Valid 3.00 12 3.7 3.7 3.7

4.00 29 9.0 9.0 12.8

5.00 43 13.4 13.4 26.2

6.00 58 18.1 18.1 44.2

7.00 67 20.9 20.9 65.1

8.00 51 15.9 15.9 81.0

9.00 30 9.3 9.3 90.3

10.00 14 4.4 4.4 94.7

11.00 7 2.2 2.2 96.9

12.00 5 1.6 1.6 98.4

13.00 3 .9 .9 99.4

14.00 1 .3 .3 99.7

15.00 1 .3 .3 100.0

Total 321 100.0 100.0

As seen in table 2, 26.1% of participants obtained a score <5 on the PSQI and were defined as having ‘good sleep’ while 73.9% obtained a score >5 and were consequently defined as having ‘poor sleep’. This was used to categorize and interpret sleep quality.

Discussion

This study aimed to address the gap in research regarding the impact of state anxiety on the relationship between sleep disturbance and depressive symptomology in a non-clinical population. As expected the present study demonstrated a significant relationship between sleep disturbance (PSQI score) and depressive symptoms (DASS-21 depression subscale), which was maintained independent of state anxiety (DASS-21 anxiety subscale) influence. Therefore there is a definite and independent relationship between sleep disturbance and depressive symptoms in non-clinical populations. However, the strength of the correlation between sleep disturbance and depression was decreased when anxiety was controlled for, indicating that anxiety did have some confounding effect on sleep disturbances.

Consistent with past findings, this study has demonstrated that a definite and independent relationship exists between depression and sleep disturbances. Slaughter (2005) acknowledges that the high co-occurrence may be explained by the excessive neuronal cell loss caused by depression, which interferes with sleep initiation. In turn, the sleep disturbances dampen normal brain metabolism and restoration during sleep. This study has also suggested that there is a positive correlational relationship between increasing depressive symptoms and greater sleep disturbance. Soehner, Kaplan and Harvey (2014) have further confirmed that the more severe the level of depressive symptoms, the greater the level and quantity of sleep disturbances and the more clinical help required. Despite the overwhelming research supporting the existence of a relationship between sleep disturbance and depression, our study also showed that anxiety did have some contribution to the severity of sleep disturbance.

The smaller effect size in the partial correlation when anxiety was controlled indicates that both depression and anxiety contribute to sleep disturbances. This is consistent with previous findings of the high level of comorbidity between these two mental disorders of up to 90% (Tiller, 2012). These results support previous research that has suggested