Strengths and Limitations of the Edinburgh Postnatal Depression Scale

How good are we at finding postnatally depressed women so we can offer support and/or treatment? If we use gut instinct or professional or clinical judgement we find a combined misdiagnosis rate — women assessed as depressed when they are not and vice versa — of 40 per cent. Briscoe⁽¹⁾ found this with health visitors in the 1980s. We found similar results in Cambridge in the 1990s⁽²⁾ A small study in a group of seven general practices in Bolton; found similar high levels of misdiagnosis.

However, Hearn⁽³⁾ also reported that without the EPDS, 13 women were classed as depressed by the primary health care team and that, later, 30 were found to be depressed by using the EPDS. They concluded the EPDS should be used routinely in primary care.

So what is this EPDS?

Women are asked to read each of the 10 statements and then underline the response that best fits how they have been feeling over the past seven days. So it is a self-rating scale. It rates the severity of some symptoms of depression and anxiety.

Its scoring system is such that:

• lowest severity of symptoms scores zero
• maximum possible score for worst severity of symptoms is 30

The EPDS was designed by Cox, Holden and Sagovsky⁽⁴⁾ in the 1980s to be used by health professionals in primary care. It takes into account the physical changes women encounter during pregnancy and postnatally. However, it doesn't include all the criteria for diagnosis of clinical depression and only focuses on one week, instead of the two demanded by diagnostic criteria for depression.

Strengths of the EPDS

• It consists of only 10 items, so for most clients it takes only a few minutes to complete. This is important, as concentration is often impaired during pregnancy, postnatally and in depression.
• Usually clients understand well what is being asked, but of course that does not mean that understanding should not be checked out with mothers.
• With proper preparation and presentation the EPDS is highly acceptable to women
• Where it is refused, the difficulty is often around ownership. Whose bit of paper is it? Are we offering it in order to find out if this client is depressed, or to facilitate discussion at the emotional level? Some of our clients, who view us as the "health police", may be understandably suspicious of our motives. There is still widespread belief that we will take the baby away from the mother.
• It offers the potential of providing equity of service: a screening programme necessarily involves all the population at which it is aimed. We now know of many instances where women who have not been offered the EPDS seek out their health visitor and ask for it. Many women want this opportunity to discuss their feelings.
• There are many questionnaires used as aids in detecting depression (for example, the Beck Depression Inventory, BDI) but the EPDS is the only one specifically designed for this population, and for primary care use.
• It has been validated by a number of studies — both during pregnancy and postnatally — the largest of which was the Cambridge one published in 1990⁽⁵⁾.

Validation of the EPDS

A validation study assesses the ability of a questionnaire to detect symptoms compared with a structured psychiatric interview. The validity of the instrument (in this case the EPDS questionnaire) is expressed by such measures as.

• 'sensitivity': the percentage of depressed women correctly identified
• 'specificity': the percentage of non-depressed women correctly identified
• 'positive predictive value': the percentage of women identified as depressed who are truly depressed.

This validation study is derived from a community sample in Cambridge in 1986-88⁽⁶⁾. Women were approached on the postnatal ward. Only 1.3 per cent declined to participate. The EPDS was mailed to them some six weeks later. There was a very impressive 97 per cent return rate, highlighting its acceptability to women.

Taking the usual EPDS cut-off of 12-13, a sensitivity of 67.7 per cent was found and positive predictive value of 66.7 per cent. That is to say about two out of three women scoring over this cut-off are correctly identified as depressed leaving one out of three who are not depressed (false positives).

At a cut-off of seven to eight, the sensitivity is "given as 93 per cent that is, seven per cent of those who are depressed score below this cut-off (false negatives), a very small number, but no less important than being depressed with a higher score. No current scale can offer 100 per cent detection rate.

Limitations of the EPDS

The scale is only as good as the person interpreting it. Where there is no, or inadequate, training individual health visitors will use it as best they can, but this may not be good enough.

We have already looked at the problem of false positives and negatives, by the use of cut-off scores which exclude clinical judgement, but there are other difficulties.

• Literacy: some people have difficulty reading, do they always tell us? The scale was never meant to be read out to women, but occasionally it is.
• Cultural issues: there are well known problems with the EPDS used by other cultures
• Misinterpretation of some of the questions: this is where understanding needs to be checked out, particularly in question 10. Self-blame and thoughts of self-harm are common in depression and may highlight the individual's ability to downplay the severity of symptoms.
• Misuse: over the years the EPDS has been used in a number of ways never originally intended.
  
  For example:
  
  
  • being left in the house to be completed and either brought back to clinic or collected at some later date. Who completed it? The mother or the mother and another person?
  • given out in clinic, with the risk of a public emotional collapse.
  • filed away in the notes (or somewhere else) without discussion with the client.

There are others. I have heard that in one area, all women saying anything positive on question 10 must be referred to the child protection team. What better way to make sure women don't feel free to be honest and share their anxieties and concerns, particularly about this most important of issues?