National Perinatal Epidemiology Unit, University of Oxford, UK
Department of Psychology, University of Reading UK
National Perinatal Epidemiology Unit, University of Oxford, UK
Correspondence: Dr Stavros Petrou, National Perinatal Epidemiology Unit, Institute of Health Sciences, University of Oxford, Old Road, Headington, Oxford OX37LF, UK. Tel: +44 (0) 1865 226829; fax: +44 (0) 1865 227002; e-mail: stavros.petrou{at}perinat.ox.ac.uk
Funding was provided by the NHS Executive South East, the Department of Health and the Tedworth Charitable Trust.
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ABSTRACT |
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Aims To estimate the economic costs of post-natal depression in a geographically defined cohort of women at high risk of developing the condition.
Method Unit costs were applied to estimates of health and social care resource use made by 206 women recruited from antenatal clinics and their infants. Net costs per motherinfant dyad over the first 18 months post-partum were estimated.
Results Mean motherinfant dyad costs were estimated at £2419.00 for women with post-natal depression and £2026.90 for women without post-natal depression, a mean cost difference of £392.10 (P=0.17). The mean cost differences between women with and without post-natal depression reached statistical significance for community care services (P=0.01), but not for other categories of service. Economic costs were higher for women with extended experiences of the condition.
Conclusions The results of this study should be used to facilitate the effective planning of services by different agencies.
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INTRODUCTION |
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METHOD |
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Study sample
Consecutive primiparous women attending antenatal clinics at 26-28 weeks of
gestation in the town of Reading, south-east England, during the period May
1997 to April 1999 were screened using a predictive index for post-natal
depression (Cooper et al,
1996). The index contained 17 items and covered women's
experiences of pregnancy, previous depressive episodes, relationships with
their current partner and mother, educational qualifications and satisfaction
with the area lived in. Women identified as being at high risk of developing
post-natal depression (index score 24) were approached by a member of the
research team and their consent to participate in the study was sought.
Consenting women resident in Reading South were entered into a randomised
controlled trial of a preventive intervention for post-natal depression
delivered by trained health visitors, whereas those resident in Reading North
were observed over the same study period and assessed using the same clinical,
psychological and economic instruments. Further details of the design and
conduct of the trial conducted in Reading South are reported elsewhere
(Cooper & Murray, 1996).
For the purposes of the economic study reported here, all economic data were
pooled across the two geographical areas and included women in the trial and
in the observational study. An independent researcher, blind to intervention
status, assessed the mental state of all women at 8 weeks, 18 weeks, 12 months
and 18 months post-partum using the Structured Clinical Interview for
DSMIIIR diagnoses (SCIDII;
First et al, 1995).
Ethical approval for the study was obtained from the relevant local ethics
committees.
Resource-use data
Data about the use of resources for all women enrolled in the study and
about the subsequent care received by their infants were obtained during the
course of three face-to-face interviews with the women. The interviews were
held at a university psychology department at 18 weeks, 12 months and 18
months post-partum. As part of all three interviews, the women were asked a
series of structured close-ended questions by one of two trained interviewers.
The interview held at 18 weeks post-partum recorded total service utilisation
over the previous 18 weeks, including all health (hospital and community) and
social care services. The interviews held at 12 months and 18 months
post-partum recorded total service utilisation over the period since the last
interview. The following information was recorded at each interview: the
professional and agency that provided the service; its location; the frequency
of use; and the duration of each service contact. Any misunderstandings about
service encounters for either the woman or infant were resolved following
discussion between the interviewer and each woman. All resource-use data were
entered directly from the research instruments completed by the interviewers
into a purpose-built data collection program with in-built safeguards against
inconsistent entries and then verified by dual coding. Estimates of service
provision were derived from these data and usually expressed in terms of
contact hours. For all hospital admissions, estimates of service provision
were expressed in terms of patient days, with part of a day at each level of
care counted as a 24-hour period.
Unit costs
Unit costs for resources used by the women and infants who participated in
the study were obtained from a variety of sources. All unit costs employed
followed recent guidelines on costing health and social care services as part
of economic appraisal (Drummond et
al, 1997). The calculation of these costs was underpinned by
the concept of opportunity cost. An average cost per hospital in-patient day
was calculated using information made available by local hospital finance
departments. All staff costs included salary information obtained from the
finance departments, as well as national insurance costs, superannuation
costs, other employer on-costs and revenue and capital overheads. Drug costs
were obtained from the British National Formulary
(British Medical Association & Royal
Pharmaceutical Society of Great Britain, 2000). The unit costs of
community health and social services were largely derived from national
sources (Netten & Curtis,
2000), and took account of time spent by professionals on indirect
activities such as travelling and paper work. However, the unit costs of some
community health services were calculated from first principles using
established accounting methods (Allen &
Beecham, 1993). Unit costs were combined with resource volumes to
obtain a net cost per motherinfant dyad over the study period. All
costs are expressed in pounds sterling and valued at 2000 prices.
Statistical methods
A detailed statistical analysis plan was followed. First, women resident in
Reading South who were randomised to receive the preventive intervention were
compared with the remainder of the women in the study in order to establish
whether receipt of the intervention significantly altered resource
utilisation. It was established that women resident in Reading South receiving
the preventive intervention received significantly more visits from their
health visitor, but did not differ significantly in terms of any other aspect
of resource utilisation. It was decided, therefore, to transpose the level of
health visitor support received by these women with the mean number of health
visitor contacts made by women resident in Reading South and allocated to
receive routine primary care, and to test the implications of this assumption
in a rigorous sensitivity analysis. Otherwise, all estimates of resource use
incorporated into the baseline statistical analyses were derived from
information provided by the women during the course of the interviews.
The primary analysis was of total costs, but results are also given by individual resource-use and cost components and by cost sector. Comparisons were made between groups of women according to whether they experienced post-natal depression or not at any time point, as measured by the SCIDII, and according to the number of times that post-natal depression was diagnosed. The statistical approach developed by Lin et al (1997) was used to simulate costs for 15 women for whom one of the economic questionnaires was not completed and whose responses could therefore be described as censored. This involved dividing the cost data-set into discrete periods and then applying the KaplanMeier method to estimate costs for each period on the basis of the uncensored cases. Costs accruing beyond the first year post-partum were reduced to present values using the 6% discount rate currently recommended for the public sector in Great Britain (National Institute for Clinical Excellence, 2001).
All results are reported as mean values with standard deviations, and mean differences in costs with 95% confidence intervals (CIs) where applicable. As the data for costs were skewed, in addition to Student t-tests of cost differences, assuming equality of variances, we used bootstrap estimation to derive 95% CIs of mean cost differences between the groups (Dixon, 1993). Each of these confidence intervals was calculated using 2000 bias-corrected bootstrap replications. Furthermore, a multiple regression model was constructed in order to identify clinical and socio-demographic predictors of economic costs. Total motherinfant dyad costs acted as the dependent variable in the regression model; a diagnosis of post-natal depression during the study period, maternal age, educational level, employment status, socio-economic status, living arrangements and the experience of problems with the partner, finance, accommodation and local area acted as explanatory variables. All analyses were performed with a micro-computer using the Statistical Package for the Social Sciences (SPSS version 7.5; SPSS Inc., Chicago, IL, USA) and SAS (SAS Institute Inc., Cary, NC, USA) software.
Sensitivity analysis
A series of multi-way sensitivity analyses was undertaken to explore the
implication of uncertainty on the base-case cost estimates. Changes in four
key variables were considered and the resulting effects on care costs were
estimated. First, three alternative scenarios of community service utilisation
were tested in response to a tendency, on the part of women, to underreport
community service utilisation that had been revealed by an earlier pilot study
(Petrou et al, 2002).
In scenario 1, community service utilisation by the motherinfant dyads
was assumed to be 10% greater than reported by the women. In scenario 2,
community service utilisation by the motherinfant dyads was assumed to
be 20% greater than reported by the women, whereas in scenario 3, community
service utilisation was assumed to be 30% greater. Second, two alternative
scenarios of per diem costs for in-patient care were tested to reflect
variations in the relative price structures of resource inputs in other
hospital settings (Drummond et
al, 1997). In scenario 1, the per diem costs for in-patient
care were assumed to be 20% less than those generated by our accounting
methods. In scenario 2, the per diem costs for in-patient care were assumed to
be 20% greater than those generated by our accounting methods. Third, two
alternative scenarios of health visitor support provided to women in Reading
South receiving the preventive intervention were tested. In scenario 1, the
level of health visitor support was set at the mean number minus one standard
deviation of health visitor contacts made by women in the Reading South
control group. In scenario 2, the level of health visitor support was set at
the mean number plus one standard deviation of health visitor contacts made by
women in the Reading South control group. Finally, we tested the impact of
four alternative discount rates (0%, 1.5%, 3% and 10%) that were applied to
costs that accrued beyond the first year post-partum.
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RESULTS |
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Table 1 presents the baseline socio-demographic and clinical characteristics of the 206 study participants. The age profile of these women closely resembled national norms for new mothers (Macfarlane & Mugford, 2000). A total of 70 women were diagnosed with post-natal depression using the SCID-II at one or more time points during the study period: 34 were diagnosed at 8 weeks post-partum; 37 at 18 weeks post-partum; 28 at 12 months post-partum; and 18 at 18 months post-partum. Study participants with (n=70) and without (n=136) post-natal depression were similar in terms of the majority of baseline characteristics, with the exception of their educational qualifications (P=0.01) and degree of satisfaction with the area lived in (P=0.03).
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Costs
Resource-use values were combined with unit costs
(Table 2) to generate estimates
of mother-infant care costs between delivery and 18 months post-partum.
Table 3 presents the mean costs
and mean cost differences per motherinfant dyad through the duration of
the study according to cost category and post-natal depression group. The
arithmetic mean cost of community care provided to the mother was estimated at
£786.20 for study participants with post-natal depression and
£505.70 for study participants without post-natal depression: a mean
cost difference of £280.50 that reached statistical significance
(P=0.01). The arithmetic mean cost difference between the post-natal
depression groups tended towards statistical significance for community mental
health care services (P=0.07) and reached statistical significance
for other community care services (P < 0.01). There were no
statistically significant differences between study participants with and
without post-natal depression in terms of the arithmetic mean cost of day care
(P=0.77), hospital out-patient care (P=0.42) and hospital
in-patient care (P=0.50) provided to the mother, and in terms of the
arithmetic mean cost of paediatric and child care (P=0.82). The
arithmetic mean motherinfant dyad cost was estimated at £2419.00
for study participants with post-natal depression and £2026.90 for study
participants without post-natal depression (mean cost difference
£392.10, P=0.17).
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The cost of health and social care increased with the number of diagnoses of post-natal depression; the arithmetic mean cost difference increased from £354.40 when women with a diagnosis of post-natal depression at one time point was used as the reference group (P=0.33) to £824.70 when women with a diagnosis of post-natal depression at two time points was used as the reference group (P=0.09). In addition, the multiple regression analysis showed that, following adjustments for potentially confounding factors, a diagnosis of post-natal depression was associated significantly with total motherinfant dyad costs (P=0.04). All other variables incorporated into the multiple regression analysis, including maternal age, educational level, employment status, socio-economic status, living arrangements and the experience of problems with the partner, finance, accommodation and local area failed to show a significant association with total motherinfant dyad costs.
Sensitivity analysis
The effects of plausible variations in the values of variables over which
there was a degree of uncertainty are presented in
Table 4. Assuming that
community service utilisation by the motherinfant dyads was greater
than reported by the women had the effect of increasing the cost difference
between the post-natal depression groups. The cost difference between women
with and without post-natal depression increased by £28.10 (from
£392.10 to £420.20) when community service utilisation was assumed
to be 10% greater than reported by the women. The cost difference increased by
£56.10 (from £392.10 to £448.20) when community service
utilisation was assumed to be 20% greater than reported by the women and by
£84.20 (from £392.10 to £476.30) when community service
utilisation was assumed to be 30% greater. A 20% reduction and increase in the
per diem cost for in-patient care had the effect of reducing and increasing
the cost difference between the post-natal depression groups by £9.70.
Reducing and increasing by one standard deviation the mean level of health
visitor support provided to women in Reading South receiving the preventive
intervention had the effect of increasing the cost difference between the
post-natal depression groups by £7.50 and £9.80, respectively.
Finally, variations in the rate at which costs that accrued beyond the first
year post-partum were discounted to present values had a marginal effect, the
largest of which was a £9.50 increase in the cost difference between the
post-natal depression groups when these costs were left undiscounted.
Simultaneous variation of the key economic variables did not significantly
affect the results of the sensitivity analysis (data available from the
authors upon request).
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DISCUSSION |
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Study limitations
The study does have limitations, which should be borne in mind. By focusing
on the cost of health and social care services provided to women and their
infants, this study has adopted a public sector perspective. Adopting a
broader, societal perspective would have allowed us to measure the direct
non-medical costs (e.g. travel and child care costs), indirect costs (e.g.
lost productivity) and intangible costs (e.g. costs of fear, pain and
suffering) attributable to the condition. A second limitation is the 18-month
time frame on which the economic study is based. Although the effects of
post-natal depression are felt most acutely during the first 18 months
post-partum, it is likely that the condition has longer-term consequences in
terms of health status and health service utilisation over the mother's and
infant's lifetime (Civic & Holt,
2000) and in terms of the child's educational requirements
(Sinclair & Murray, 1998; Hay et al, 2001). If
this is the case, then longer-term observational research is required to
provide a complete assessment of the condition's economic implications. A
third limitation relates to the focus of the economic study on women at high
risk of developing post-natal depression. A separate audit of the
health-seeking behaviour of women at low risk of developing post-natal
depression, conducted in the same geographical area, showed that women not at
high risk had fewer antenatal and post-natal hospital contacts and admissions
than the study participants (Murray et
al, 2000). This suggests that the high-risk population from
which the study participants were drawn might be heavier users of public
services than the primiparous population as a whole. However, there is no
evidence to suggest that the mean difference in care costs between the
post-natal depression groups (i.e. the costs that can be attributed to the
condition) is affected by the selection of the study population. Another
limitation is that the primary out-put of the statistical analyses was an
incremental cost attributable to each case of post-natal depression,
regardless of its duration. Secondary analyses showed that economic costs were
heightened among women with more than one diagnosis of post-natal depression
during the study period. As part of our future research, we hope to estimate
the economic costs of post-natal depression by overall duration of experience.
A final limitation is that the number of health visitor contacts made by
approximately one-half of the women resident in Reading South was affected by
participation in a randomised controlled trial and had to be transposed with
an alternative estimate of health visitor contacts. However, the cost of
health visitor support formed less than 1% of total public sector costs.
Furthermore, a rigorous sensitivity analysis revealed that the assumed level
of health visitor contacts had a marginal effect on overall care costs and
cost differences between the post-natal depression groups
(Table 4). Therefore, we are
confident that the assumption made does not diminish the validity of the study
conclusions.
Policy and research implications
Despite the limitations of our study, the results have important
implications for service providers. The study generated a mean cost
differential involving health and social care of £392.10 between women
with and without post-natal depression. Given that approximately 700 000 women
give birth in Great Britain each year
(Macfarlane & Mugford,
2000) and that approximately 13% of these women will subsequently
experience post-natal depression (O'Hara
& Swain, 1996), these data suggest that the national economic
burden of the condition to the public services amounts to approximately
£35.7 million per annum (sensitivity analysis range
£34.4£43.3 million). Furthermore, the economic costs of
post-natal depression are heightened among women with extended experiences of
the condition. It is imperative that public sector providers recognise the
overall economic impact of the condition in their service planning and that
particular care is taken to target services at the psychologically
vulnerable.
The prevention of mental health problems in the perinatal period and their deleterious consequences is regarded as a priority both politically (Secretary of State for Health, 1998) and professionally (Royal College of Paediatrics and Child Health, 1998). The British Government has published a number of documents that emphasise the need for effective strategies for preventing mental health problems during this period (Home Office, 1998; Department of Health, 2000). In recent years, the efficacy of a number of secondary prevention interventions for post-natal depression has been demonstrated by randomised controlled trials (Holden et al, 1989; Appleby et al, 1997; O'Hara et al, 2000). In addition, studies of a number of primary prevention interventions show promising results, but these remain to be tested in trials that are appropriately sized and comply with internationally accepted design and reporting guidelines. A feature of all the studies aimed at preventing or alleviating the effects of post-natal depression is their failure to collect detailed economic information and, therefore, to assess the cost-effectiveness of the interventions. It is imperative that economic evaluations of these interventions are conducted and that resources in this area are allocated in a manner that is both clinically and cost effective.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication May 8, 2002. Revision received July 16, 2002. Accepted for publication July 31, 2002.
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