Six hundred and twelve women received an invitation to the survey after completing an online screening survey, with 331 participants starting the actual survey. Forty-four participants dropped out of the survey; their responses were not retained for this analysis because those respondents did not complete the anger measure (the outcome variable of interest). A further 9 cases were excluded because of evidence of participant ineligibility (e.g., having an infant with health problems or premature delivery). Participants who were excluded because they withdrew or were ineligible did not differ significantly from other participants with respect to maternal age, infant age, parity, education, or income; however, excluded participants tended to be employed, and this bordered on significance (χ² (1, [N = 326]) = 3.719, p = 0.054).
Univariate Analyses
Sample Characteristics. The final sample consisted of 278 women between the ages of 23 to 44 years of age (M = 32.6, SD = 3.77) living across Canada, with the majority (77%, n = 220) being 30 years of age and over (Table 1). The sample represented high socioeconomic backgrounds with 73.0% (n = 203) holding a university degree or higher and 69.8% (n = 194) having household incomes of ≥ $90,000 CAD. All but 3 participants were partnered and just over half (53.8%, n = 149) were first-time mothers.
Research Question 1. To answer the question about the proportions of women who experienced intense anger, depressive symptoms, and poor sleep quality: 30.6% of women (n = 85) reported high levels of anger; 26% of women (n = 73) indicated probable depression (depressive symptoms above cut-off on the EPDS); and 73.3% of women (n = 204) reported global PSQI scores above cut-off, indicating problematic sleep. Of the 85 women who had high anger levels, almost 50% (n = 39) experienced probable depression, however, it is noteworthy that a large proportion of women (n = 46) had high levels of anger but did not have depressive symptoms above cut-off. When responding to a single question about sleep quality (using the PSQI item on perception of sleep quality), 52% of women (n = 144) felt their sleep quality was poor (either fairly bad or very bad).
Bivariate Analyses
In support of our hypothesis that depressive symptoms (EPDS scores >12) would be associated with higher anger levels, a chi-square test demonstrated that women who had depressive symptoms were nearly 4 times more likely to experience high levels of anger relative to those who did not have symptoms above cut-off (OR = 3.96, 95% CI [2.25 – 6.98], p < 0.001) (Figure 1). Contrary to our hypothesis, women who had a PSQI score >5 had lower odds of having high anger levels (OR = 0.49, 95% CI [0.26 – 0.92], p = 0.036). In support of our hypothesis that perceived sleep quality would be associated with anger, women who perceived their sleep as poor (fairly bad or very bad), were 2.9 times more likely to have high levels of anger compared to mothers who perceived their sleep as good (fairly good or very good) (OR = 2.88, 95% CI [1.68 – 4.96], p < 0.001) (Figure 1).
Participants who had high anger levels (n = 85, M = 33 ± 6.3) had more children, t(152.8) = 2.8, p < 0.01, and had higher scores on depressive symptoms, t(160.1) = 6.3, p < 0.01, fatigue t(212.2) = 6.01, p < 0.01, perceptions of infant sleep problems, χ2 (1, n = 278) = 11.9, p < 0.01, cognitions about infant sleep, t(168.1) = 3.76, p < 0.01, and anger about infant sleep t(144.1) = 6.03, p < 0.01. They also reported lower education levels, χ2 (3, n = 278) = 12.9, p < 0.01, income, χ2 (3, n = 277) = 11.18, p = 0.01, and perceived sleep quality, χ2 (1, n = 278) = 14.2, p < 0.01 (Table 1).
Table 2 delineates the bivariate correlations between anger scores and demographic variables, maternal-infant sleep quality, fatigue, depressive symptoms, angry cognitions about infant sleep, and social support.
Table 1
Sample Characteristics.
Characteristic
|
|
All Participants
N = 278
Mean, SD /
n (%)
|
Anger Levela
|
P value
|
Low
N = 193; n (%)
|
High
N = 85; n (%)
|
Age
|
Range 23-44 years
|
32.6 ± 3.8
|
32.6 ± 3.7
|
32.7 ± 4.1
|
0.97
|
Infant age
|
Range 6-12 months
|
8.6 ± 1.9
|
8.5 ± 2.0
|
8.7 ± 1.9
|
0.43
|
Infant sex
|
Male
|
148 (53.4)
|
105 (54.4)
|
43 (50.6)
|
0.72
|
Partnered
|
Yes
|
275 (98.9)
|
192 (99.5)
|
83 (97.6)
|
0.46
|
Parity
|
Primiparous
Multiparous
Unknown
|
149 (53.6)
128 (45.0)
1 (<1)
|
1.5 (0.73)
|
1.8 (0.76)
|
<0.01
|
Employment
|
Yes
|
50 (18.0)
|
31 (16.1)
|
19 (22.4)
|
0.28
|
Immigrant
|
Yes
|
41 (14.7)
|
33 (80.5)
|
8 (19.5)
|
0.14
|
Education
|
Postgraduate
University
College
High School
|
81 (29.1)
122 (43.9)
62 (22.3)
13 (4.7)
|
64 (33.2)
84 (43.5)
41 (21.2)
4 (2.1)
|
17 (20.0)
38 (44.7)
21 (24.7)
9 (10.6)
|
<0.01
|
Household income
|
>$110K
$90,000-109,999
$60,000-89,999
<$60,000
Unknown
|
134 (48.2)
60 (21.7)
60 (21.7)
23 (8.3)
1 (<1)
|
104 (53.9)
37 (19.2)
40 (20.7)
11 (5.7)
|
30 (35.3)
23 (27.1)
20 (23.5)
12 (14.1)
|
0.01
|
Anger (SAS)
|
Range 15-53
|
24 (7.6)
|
20.0 (3.5)
|
33 (6.3)
|
< 0.01
|
Depression symptoms (EPDS)
|
Range 0-21
|
9.3 ± 4.7
|
8.2 ± 4.4
|
11.8 ± 4.3
|
< 0.01
|
|
EPDS score >12
|
Yes
|
73 (26.0)
|
34 (46.6)
|
39 (53.4)
|
< 0.01
|
Global PSQI
|
Range 1-15
|
7.1 ± 2.4
|
6.6 ± 2.2
|
8.0 ± 2.5
|
< 0.01
|
|
Global PSQI score >5
|
Yes
|
204 (73.0)
|
134 (73.4)
|
70 (25.2)
|
0.036
|
|
Maternal sleep quality
|
Range 1-4
|
2.6 ± 0.7
|
2.4 ± 0.7
|
2.8 ± 0.6
|
< 0.01
|
Fatigue (MAF)
|
Range 7-45
|
30.3 ± 8.5
|
28.5 ± 8.7
|
34 ± 6.4
|
< 0.01
|
Infant sleep problem (BISQ)
|
Yes
|
194 (69.8)
|
122 (62.3)
|
72 (37.1)
|
< 0.01
|
Maternal cognitions about infant sleep (MCISQ)
|
Range 5-69
|
34.9 (12.7)
|
33 ± 12.7
|
39 ± 2.0
|
< 0.01
|
|
Anger
|
|
6.4 (3.9)
|
5.5 ± 3.5
|
8.5 ± 4.0
|
< 0.01
|
|
Limit Setting
|
|
14.9 (6.0)
|
14.7 ± 6.1
|
15.5 ± 5.6
|
0.26
|
|
Doubts
|
|
7.0 (4.5)
|
6.5 ± 4.3
|
8.1 ± 4.6
|
< 0.01
|
|
Safety
|
|
3.2 (2.4)
|
2.9 ± 2.4
|
3.6 ± 2.4
|
0.07
|
|
Feeding
|
|
6.5 (3.7)
|
6.3 ± 3.8
|
7.0 ± 3.3
|
0.12
|
Family support scale (FSS)
total score
|
44.8 (9.4)
|
44.8 (9.4)
|
44.7 ± 9.4
|
45.0 ± 9.4
|
0.82
|
aState Anger Scale raw score of 27 (90th percentile). bMinimum 12 hours sleep per day (Paruthi et al., 2016). |
Table 2
Pearson and Spearman Correlations of Anger and Examined Variables.
Variable
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
9
|
|
|
|
|
|
|
|
|
|
|
1. Anger
|
1.000
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2. Parity
|
0.17**
|
1.000
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
3. Education
|
-0.20**
|
-0.17**
|
1.000
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
4. Income
|
-0.18**
|
0.03
|
0.23**
|
1.000
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
5. Depression symptoms
|
0.42**
|
-0.04
|
-0.20**
|
-0.21**
|
1.000
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
6. Global PSQIa
|
0.26**
|
-0.02
|
-0.27**
|
-0.18**
|
0.37**
|
1.000
|
|
|
|
|
|
|
|
|
|
|
|
|
|
7. Perceived sleep qualityb
|
0.32**
|
0.10
|
-0.13*
|
-0.15*
|
0.27**
|
0.66**
|
1.000
|
|
|
|
|
|
|
|
|
|
|
|
|
8. Fatigue
|
0.38**
|
0.04
|
-0.04
|
-0.21**
|
0.50**
|
0.47**
|
0.54**
|
1.000
|
|
|
|
|
|
|
|
|
|
|
|
9. MCISQ anger
|
0.42**
|
-0.03
|
-0.09
|
-0.14*
|
0.32**
|
0.28**
|
0.32**
|
0.42**
|
1.000
|
|
|
|
|
|
|
|
|
|
|
10. Support
|
-0.02
|
0.08
|
0.14*
|
0.06
|
-0.11
|
-0.07
|
-0.05
|
-0.10
|
-0.06
|
Note. * indicates p < 0.05. ** indicates p < 0.01. aGlobal PSQI total score (>5 indicates problematic sleep). bPSQI item on perceived sleep quality. |
Multivariate Analyses
Research Question 2. Preliminary model building was carried out using linear regression (Table 3) to answer the second question about variables associated with maternal anger. A priori variables that were tested included income, education, immigration status, depressive symptoms, fatigue, maternal sleep quality, angry cognitions about infant sleep, and social support. Parity was included because maternal report of the number of children demonstrated a significant correlation with anger. The single item capturing maternal perception of sleep quality was chosen over the PSQI global score because the extant literature has indicated that mood disturbances (e.g., depression) are better predicted by individuals’ perceptions of sleep quality [58–60]. In the first step, demographic variables explained a small but significant proportion of the variance in anger, with income and parity demonstrating significant associations, R2 = 0.084, F (4, 271) = 6.23, p < 0.001. In the second step, depressive symptoms, sleep quality, fatigue, anger about infant sleep, and social support contributed to a model that explained 34% of the variance in maternal anger, R2 = 0.341, F (9, 261) = 15.03, p < 0.001; parity, depressive symptoms, and anger about infant sleep were significantly associated with maternal anger. Given that large standard errors were identified for fatigue and sleep quality and that these constructs have theoretical overlap, in the third step of model development, when maternal fatigue was removed, sleep quality was significantly associated with maternal anger (with worse perceived sleep quality associated with greater anger), R2 = 0.330, F (8, 265) = 16.35, p < 0.001.
Examination of the residuals in the second and third linear models revealed moderate violations of the assumptions of equal variances (heteroscedasticity) and normality. While moderate degrees of non-normality can generally be tolerated in linear regression, heteroscedasticity can lead to biased standard errors and significance values [57, 61]. Robust regression was employed to improve the accuracy of beta coefficient and significance estimates in the final model (Table 4). In partial support of our hypothesis that socioeconomic status indicators would be associated with anger, income was associated with anger in the robust regression model (b = -0.83, p < 0.05). Education (b = -0.28, p = 0.29) and immigration status (b = -0.71, p = 0.43) were not significantly associated with maternal anger. Consistent with our hypothesis, maternal sleep quality (b = 1.08, p = 0.02) and anger about infant sleep (b = 0.5, p < 0.01) were associated with maternal anger. Contrary to our expectations, social support was not associated with anger in our model (b = 0.05, p = 0.11).
Table 3
Linear Model Building Explaining Maternal Anger
|
Linear Model 1
|
Model 2
|
Model 3
|
Variable
|
B (SE)
|
CI
|
t
|
p
|
B (SE)
|
CI
|
t
|
p
|
B (SE)
|
CI
|
t
|
p
|
(Intercept)
|
.07 (.48)
|
[-.87, 1.02]
|
-.15
|
.88
|
-.16 (.42)
|
[-.67, .98]
|
.38
|
.707
|
-.22 (.42)
|
[-.61, 1.04]
|
.51
|
.607
|
Income
|
-1.14 (.4)
|
[-2.0, -0.5]
|
-2.61
|
.009
|
-.37 (.39)
|
[-1.14, .4]
|
-.94
|
.348
|
-.49 (.39)
|
[-1.25, .27]
|
-1.27
|
.206
|
Immigrant-Yes
|
-.50 (1.3)
|
[-2.9, 2.0]
|
-.40
|
.691
|
-1.05 (1.2)
|
[-3.32, 1.2]
|
-.91
|
.363
|
-1.16 (1.1)
|
[-3.40, 1.07]
|
-1.02
|
.307
|
Education
|
-.72 (.33)
|
[-1.4, -.07]
|
-2.17
|
.031
|
-.33 (.30)
|
[-.92, .26]
|
-1.1
|
.270
|
-.26 (.30)
|
[-.84, .32]
|
-.87
|
.385
|
Parity
|
1.6 (.62)
|
[.41, 2.84]
|
2.64
|
<.009
|
1.6 (.54)
|
[.49, 2.63]
|
2.87
|
.004
|
1.66 (.54)
|
[.59, 2.72]
|
3.06
|
.002
|
Depression
|
|
|
|
|
.44 (.10)
|
[.25, .63]
|
4.48
|
<.001
|
.46 (.09)
|
[.29, .64]
|
5.17
|
<.001
|
Sleep Quality
|
|
|
|
|
1.11 (.67)
|
[-.21, 2.42]
|
1.65
|
.099
|
1.35 (.60)
|
[.17, 2.53]
|
2.24
|
.026
|
Fatigue
|
|
|
|
|
.07 (.06)
|
[-.06, .19]
|
1.05
|
.296
|
|
|
|
|
Infant sleep anger
|
|
|
|
|
.52 (.11)
|
[.31, .74]
|
4.74
|
<.001
|
.55 (.11)
|
[.33, .76]
|
5.07
|
<.001
|
Support
|
|
|
|
|
.03 (.04)
|
[-.05, .12]
|
.71
|
.476
|
.02 (.04)
|
[-.06, .11]
|
.51
|
.607
|
Observations
|
276
|
271
|
274
|
R2 / R2 adjusted
|
.08 / .07
|
.341 / .319
|
.33 / .31
|
Note: Beta coefficients are unstandardized. Bolding indicates statistical significance.
|
Table 4
Robust Regression Model Explaining Maternal Anger
|
Robust Model
|
Variable
|
B (SE)
|
CI
|
t
|
p
|
(Intercept)
|
-.16 (.46)
|
[-1.76, .04]
|
-1.87
|
.062
|
Income
|
-.83 (.37)
|
[-1.56, -.09]
|
-2.21
|
.028
|
Immigrant-Yes
|
-.71 (.90)
|
[-2.47, 1.1]
|
-.79
|
.431
|
Education
|
-.28 (.27)
|
[-.81, .24]
|
-1.06
|
.292
|
Parity
|
2.08 (.52)
|
[1.06, 3.10]
|
4.00
|
<.001
|
Depression
|
.35 (.08)
|
[.18, .51]
|
4.11
|
<.001
|
Sleep Quality
|
1.08 (.67)
|
[.15, 2.0]
|
2.29
|
.023
|
Infant sleep anger
|
.50 (.12)
|
[.27, .72]
|
4.24
|
<.001
|
Support
|
.05 (.03)
|
[-.01, .12]
|
1.60
|
.111
|
Observations
|
274
|
R2 / R2 adjusted
|
.390 / .371
|
Note: Beta coefficients are unstandardized. Bolding indicates statistical significance.
|