Descriptive characteristics of the study participants
Descriptive characteristics of the participants from the two population samples are presented in Table 1.
In the survey for the clinical sample the parents were asked to describe the main reason for why they as a family needed the treatment at the IMH unit. Of the mothers, 71% reported the main reason for needing the treatment at the IMH unit as their own difficulties, either concerning their parenting (46%) or difficulties due to mental health issues (25%), while 3% reported the main reason was difficulties for their partner. Of the fathers, 41% reported the main reason being their own difficulties (33% concerning their parenting, 8% due to mental health issues), and 36% reported difficulties for their partner as the main reason. Other main reasons were difficulties for the child (e.g., externalising, and internalising behaviours, and feeding problems), reported as the main reason by 22% of the parents in total (not shown in Table).
Table 1
Descriptive characteristics of study participants in the community (Scania Birth Cohort) and the clinical (infant mental health unit) population samples
| | Community sample | | Clinical sample |
| | Mothers N = 65 | Fathers N = 57 | | Mothers N = 100 | Fathers N = 82 |
Parental age years mean (SD) | | 31.2 (4.0) | 32.2 (5.6) | | 33.4 (4.9) | 34.9 (5.5) |
Child age months mean (SD) | | | | | 12.7 (13.2) | 10.9 (12.2) |
At T1 | | 1.6 (0.7) | 1.7 (0.6) | | - | - |
At T2 | | 6.3 (0.5) | 6.5 (0.8) | | - | - |
At T3 | | 12.0 (0.6) | 12.1 (0.5) | | - | - |
Highest education n (%) | | | | | | |
Compulsory school (9 years) | | 2 (3.1%) | 3 (5.8%) | | 0 | 3 (3.7%) |
Senior high school (2–4 years) | | 19 (29.2%) | 21 (40.4%) | | 19 (19.0%) | 23 (28.0%) |
University (≤ 3 years) | | 21 (32.3%) | 15 (28.8%) | | 21 (21.0%) | 14 (17.1%) |
University (> 3 years) | | 23 (35.4%) | 13 (25.0%) | | 54 (54.0%) | 39 (47.6%) |
Post-graduate education | | 0 | 0 | | 6 (6.0%) | 3 (3.7%) |
Cohabitation status n (%) | | | | | | |
Living with the other parent | | 60 (92.3%) | 56 (98.2%) | | 86 (86.0%) | 81 (98.8%) |
Living alone | | 3 (4.6%) | 0 | | 9 (9.0%) | 1 (1.2%) |
Living with their own parents | | 2 (3.1%) | 1 (1.8%) | | 3 (3.0%) | 0 |
Other living arrangement | | 0 | 0 | | 2 (2.0%) | 0 |
Region of birth n (%) | | | | | | |
Sweden | | 59 (90.8%) | 51 (91.1%) | | 84 (84.0%) | 65 (79.3%) |
Scandinavia (not Sweden) | | 1 (1.5%) | 0 | | 3 (3.0%) | 2 (2.4%) |
Europe (not Scandinavia) | | 3 (4.6%) | 3 (5.4%) | | 7 (7.0%) | 5 (6.1%) |
Outside of Europe | | 2 (3.1%) | 2 (3.6%) | | 6 (6.0%) | 10 (12.2%) |
Information missing | | 0 | 0 | | 0 | 1 (1.2%) |
SD = standard deviation. T1–T3 = Postpartum data collection timepoints in the community sample.
PIBS internal consistency, and descriptive statistics related to score interpretability
In the community sample, the PIBS internal reliability coefficients were generally higher using the McDonald’s ω method and varied from high (ω = 0.86) to low (ω = 0.49) between timepoints (T1–T3). For the mothers they were the highest at T1 (ω = 0.85) and for the fathers at T2 (ω = 0.86). Close-to-acceptable internal consistency emerged for the fathers at T1 (ω = 0.67) and for the mothers at T3 (ω = 0.69). In the clinical sample, the PIBS internal reliability coefficients were all above 0.70 and the results were similar between the two methods Cronbach’s α and McDonald’s ω. Coefficients ranged between 0.76 and 0.89 and were somewhat higher for mothers than for fathers (Table 2).
There were no consistent patterns of internal reliability coefficients being significantly altered after deletion of single items in either parent or population group, e.g., deleting single items for the community mothers at T1 yielded McDonald’s ω coefficients ranging between ω = 0.81 and ω = 0.86. Specifically, deleting the item “Dissatisfied” (Olust in Swedish) decreased the coefficient from ω = 0.85 to ω = 0.81, while deleting either “Resentful” (Motvilja) or “Protective” (Beskyddande) increased it to ω = 0.86 (not shown in Table).
PIBS floor effects, i.e., more than 15% of participants with the lowest possible score (Terwee et al., 2007) were evident in both parent groups in both samples, with higher percentages of lowest possible score in the community compared to the clinical sample (Table 2).
Table 2
Parent-to-Infant Bonding scale (PIBS) internal reliability coefficients, central tendencies, and variability, and percentages of scale missing data and lowest possible score in mothers and fathers in the community and clinical population samples
| | Community sample (Scania Birth Cohort) | | Clinical sample (infant mental health unit) |
PIBS version | | PIBS first weeks | PIBS currently | PIBS currently | | PIBS first weeks | PIBS currently |
Child age | | T1 1 month | T2 6 months | T3 12 months | | 1–50 monthsa |
Parent group No. of participants, Nb | | Mothers N = 61 | Fathers N = 54 | Mothers N = 56 | Fathers N = 49 | Mothers N = 35 | Fathers N = 33 | | Mothers | Fathers | Mothers | Fathers |
Mothers N = 100 and Fathers N = 82 |
Internal reliability coefficient | | α | ω | α | ω | α | ω | α | ω | α | ω | α | ω | | α | ω | α | ω | α | ω | α | ω |
| .79 | .85 | .54 | .67 | .51 | .49 | .79 | .86 | .59 | .69 | .43 | .62 | | .89 | .89 | .81 | .82 | .84 | .85 | .76 | .79 |
Mean (SD) | | 1.3 (2.4) | 1.3 (1.6) | 0.4 (0.8) | 0.8 (1.7) | 0.6 (1.2) | 0.7 (1.0) | | 5.6 (5.5) | 3.7 (4.1) | 3.3 (3.5) | 2.2 (2.5) |
Median (quartiles: Q1, Q3) | | 0 (0, 1.75) | 1 (0, 3) | 0 (0, 0) | 0 (0, 1) | 0 (0, 1) | 0 (0, 1) | | 4 (1, 7.75) | 2 (0, 6) | 2 (1, 5) | 1 (0, 4) |
No. of respondingc; % missing | | 60; 1.6% | 52; 3.7% | 55; 1.8% | 48; 2.0% | 35; 0% | 32; 3.0% | | 92; 8.0% | 79; 3.7% | 99; 1.0% | 80; 2.5% |
Percent lowest possible score | | 58.3% | 46.2% | 80.0% | 60.4% | 74.3% | 59.4% | | 18.5% | 25.3% | 24.2% | 33.8% |
PIBS = Parent-to-Infant Bonding Scale. PIBS first week = reflect bonding in the first weeks (retrospectively). PIBS currently = reflect bonding in current time.
T1–T3 = Postpartum data collection timepoints for the community sample. amean child age in the clinical sample: mothers: 12.7 months; fathers: 10.9 months.
b N=No. of participants who filled in the questionnaire. α = Cronbach’s alpha coefficient. ω = McDonald’s omega coefficient. cNo. of respondents with complete PIBS data. % missing = percentage of scale missing data.
Internal consistency of the comparator instruments, and PBQ descriptive statistics related to score interpretability
McDonald’s ω coefficients for the PBQ total scale and subscales in the clinical sample were 0.70 or above except for the anxiety about care subscale (ω = 0.61 in mothers and ω = 0.66 in fathers). Percentages of lowest possible PBQ total or subscale score in mothers and fathers in the clinical sample were all < 15% (Table 3).
Table 3
Postpartum Bonding Questionnaire (PBQ) internal reliability coefficients, central tendencies, and variability, and percentages of scale missing data and lowest possible score in the clinical sample. Mothers N = 100, Fathers N = 82
PBQ total or subscale | | PBQ total | PBQ IB | PBQ RA | PBQ AC | | PBQ total | PBQ IB | PBQ RA | PBQ AC |
Parent group | | Mothers | | Fathers |
Internal reliability coefficient | | α | ω | α | ω | α | ω | α | ω | | α | ω | α | ω | α | ω | α | ω |
| .90 | .91 | .85 | .86 | .80 | .81 | .59 | .61 | | .89 | .89 | .82 | .83 | .68 | .70 | .62 | .66 |
Mean (SD) | | 24.4 (13.5) | 13.1 (7.5) | 6.1 (4.6) | 5.2 (3.2) | | 17.7 (11.7) | 9.8 (6.6) | 4.5 (3.5) | 3.5 (2.9) |
Median (quartiles: Q1, Q3) | | 23 (14.75, 31) | 13 (7, 17) | 5 (3, 9) | 9 (3, 7) | | 15 (8.5, 24) | 8.5 (5, 13.25) | 4 (1, 7) | 2 (1, 5) |
No. of respondinga; % missing | | 90; 10% | 91; 9.0% | 97; 3.0% | 100; 0% | | 77; 6.1% | 78; 4.9% | 79; 3.7% | 81; 1.2% |
Percent lowest possible score | | 1.1% | 1.1% | 8.2% | 2.0% | | 3.9% | 2.6% | 12.7% | 9.9% |
PBQ total = Postpartum Bonding Questionnaire total scale (23 items). IB = impaired bonding (12 items). RA = rejection and anger (7 items). AC = anxiety about care (4 items).
α = Cronbach’s alpha coefficient. ω = McDonald’s omega coefficient.
aNo. of respondents with complete PBQ data. % missing = percentage of scale missing data.
In the community sample at T1–T3, all internal reliability coefficients (Cronbach’s α and McDonald’s ω) of the EPDS, DASS-D, and DASS-A were above 0.70, ranging between 0.73 and 0.93. In the clinical sample, the DASS-D and DASS-A internal reliability coefficients ranged between 0.83 and 0.89 (not shown in Table).
PIBS correlations in the clinical population sample
The PIBS currently scores correlated strongly with the PBQ total scores, and with scores of the PBQ impaired bonding, and rejection and anger subscales in both mothers and fathers, rs=0.74 to rs=0.80, all p < 0.001. The correlations between the PIBS and PBQ anxiety about care scores were lower, rs=0.35 for mothers, and rs=0.49 for fathers, both p < 0.001 (Table 4).
The correlations between PIBS first weeks and PIBS currently scores in the clinical sample were rs=0.51 for mothers, and rs=0.66 for fathers, both p < 0.001 (not shown in Table).
PIBS correlations with the EPDS, DASS-D, and DASS-A
In the community and clinical samples, the correlations between PIBS scores and EPDS, DASS-D, and DASS-A scores, respectively, for mothers and fathers were all < 0.60 (Table 5).
Table 4
Correlations between the PIBS and PBQ total and subscale scores in the clinical sample. Correlation coefficients for mothers (N = 100) and fathers (N = 82) are displayed below and above the diagonal, respectively
| PIBS currently | PBQ total | PBQ IB | PBQ RA | PBQ AC |
PIBS currently | - | .76*** | .74*** | .80*** | .49*** |
PBQ total | .76*** | - | .95*** | .88*** | .80*** |
PBQ IB | .76*** | .95*** | - | .78*** | .67*** |
PBQ RA | .76*** | .92*** | .82*** | - | .57*** |
PBQ AC | .35*** | .62*** | .46*** | .45*** | - |
PIBS currently = Parent-to-Infant Bonding Scale reflecting bonding in current time.
PBQ total = Postpartum Bonding Questionnaire total scale (23 items). IB = impaired bonding (12 items). RA = rejection and anger (7 items). AC = anxiety about care (4 items).
The mothers’ correlation coefficients are displayed below the diagonal. The fathers’ correlation coefficients are displayed above the diagonal. ***p < 0.001
Table 5
Correlations between PIBS scores and mental health measurements scores in the community and clinical samples. Correlation coefficients for mothers and fathers are displayed below and above the diagonals, respectively
| | Community sample | | Clinical sample |
Child age | | 1 month Mothers N = 61 Fathers N = 54 | | 6 months Mothers N = 56 Fathers N = 49 | | 12 months Mothers N = 35 Fathers N = 33 | | 1–50 months1 Mothers N = 100 Fathers N = 82 | |
| | PIBS | EPDS | DASS-D | DASS-A | PIBS | EPDS | DASS-D | DASS-A | PIBS | EPDS | DASS-D | DASS-A | | PIBS | DASS-D | DASS-A |
PIBS | | - | .46*** | .37* | .20 | - | .31* | .29 | .23 | - | .10 | .22 | .05 | | - | .44*** | .36** |
EPDS | | .25 | - | .65*** | .44** | .17 | - | .65*** | .64*** | .10 | - | .65*** | .36* | | n/a | n/a | n/a |
DASS-D | | .37** | .76*** | - | .52*** | .19 | .74*** | - | .55*** | .31 | .77*** | - | .24 | | .54*** | - | .45*** |
DASS-A | | .28* | .64*** | .66*** | - | .04 | .58*** | .43*** | - | .25 | .41*** | .55*** | - | | .27** | .67*** | - |
1mean child age for the mothers: 12.7 months; mean child age for the fathers: 10.9 months.
PIBS = Parent-to-Infant Bonding Scale. Community sample 1-month PIBS scores reflect bonding retrospectively in the first weeks, all other PIBS scores reflect current time.
EPDS = Edinburgh Postnatal Depression Scale. DASS = Depression Anxiety Stress Scales. DASS-D = DASS depression scale. DASS-A = DASS anxiety scale
Mothers’ correlation coefficients are displayed below the diagonals. Fathers’ correlation coefficients are displayed above the diagonals.
*p < 0.05; **p < 0.01; ***p < 0.001. n/a = not applicable.
Comparisons of PIBS scores between groups and between timepoints within groups
The median PIBS first weeks as well as currently scores in the clinical sample were higher, indicating a higher risk of bonding difficulties, than PIBS scores in the community sample (T1–T3) for both mothers and fathers (Table 2), with medium to large effect sizes (r), U = 1326.50, z=-3.51, p < 0.001, r = 0.31 to U = 999.50, z=-6.81, p < 0.001, r = 0.55.
In the community sample, mean PIBS scores were higher at T1 compared with scores at T2 and T3 in both mothers and fathers (Table 2) with small to medium effect sizes (w2), F(1.7, 52.6) = 3.61, p = 0.041, w2 = 0.05, and F(1.8, 48.3) = 3.48, p = 0.044, w2 = 0.038 respectively. Planned contrasts revealed there was no significant difference between T2 and T3, but there was a significant reduction in PIBS scores between T1 and T2, F(1, 31) = 5.42, p = 0.027 for the mothers, and F(1, 27) = 6.24, p = 0.019 for the fathers.
In the clinical sample, the PIBS first weeks scores, retrospectively reflecting bonding in the first weeks, were higher than the PIBS currently scores in both mothers and fathers (Table 2), with medium effect sizes, T = 571.5, p < 0.001, r = 0.47, and T = 314.0, p < 0.001, r = 0.42 respectively. Further, the mothers reported higher PIBS first weeks, as well as currently scores than the fathers (Table 2), with small effect sizes, U = 2899.50, z=-2.29, p = 0.022, r = 0.18, and U = 3283.00, z=-2.00, p = 0.046, r = 0.15 respectively.