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Since , outpatient visits were also registered. Because some patients with substance abuse disorders are treated only in somatic departments, we decided to include patients in the National Hospital Register 21 who had a diagnosis of substance use disorders ICD-8 codes , Identifying deliberate self-harm in Danish registers is rather complicated because procedures have changed, and some procedures are not well complied with. We have identified deliberate self-harm in the different periods with different algorithms. After , suicide attempts were identified as people fulfilling at least 1 of the following criteria in the National Hospital Register or Danish Psychiatric Central Register:.

Any psychiatric diagnosis ICD chapter F and a comorbid diagnosis of poisoning with medication and biological compounds ICD codes T36 through T50 or nonmedical compounds, excluding alcohol and poisoning from food T52 through T60 ;. Any contact with a hospital because of poisoning with weak or strong analgesics, hypnotics, sedatives, psychoactive drugs, antiepileptics, and antiparkinsonian drugs or carbon monoxide ICD codes T39, T42, T43, and T58 ; and.

The classification of deliberate self-harm was identical to that used previously. Analyses of deliberate self-harm were only possible beginning in ; therefore, the follow-up for these analyses is no longer than 30 complete years. For each mental disorder, cohort members were followed up from their first hospital contact as inpatients or outpatients after 15 years of age until suicide, death from other causes, emigration from Denmark, disappearance, or December 31, whichever came first.

Attributable Risk & Absolute Risk Reduction

Because we aimed to study suicidal behavior among adolescents, we excluded from the analyses individuals who had their psychiatric disorder before 15 years of age. By selecting only persons born in and later, we ensured that the cohort consisted of incident cases, as the number of persons who had their first hospital contact owing to one of the mental disorders of interest before 15 years of age is very small.


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Competing risks survival analyses 15 allowed us to calculate the absolute risks of suicide or cumulative incidences as the percentages of persons in the population who had committed suicide at a given time since the onset of the disorder of interest, taking into account that people may migrate or die of other causes. These analyses were made for each sex and were subdivided according to the age at onset of the disorder of interest.

In this report, our interest is the probability of suicide. This probability, also referred to as the cumulative incidence , is not a simple function of the incidence rate of suicide; rather, it is estimated as the weighted integral of the incidence rates, in which the weights equal the survival function. In this situation, people born in contribute to the estimation of the incidence rate from time 0 to time 36, whereas people born in only contribute to the estimation of the incidence rate until 1 year after the first psychiatric contact.

To estimate the cumulative incidence of suicide among people with no history of mental illness, we adopted a slightly alternative strategy. Because this healthy population was selected at random among all 2. In addition, we performed analyses of comorbidity. Patients who had a diagnosis of substance abuse disorder plus any other mental disorder—at the same time or at different times—underwent separate analyses. Similarly, we performed analyses of comorbidity for patients with unipolar affective disorder in combination with other psychiatric disorders and any history of hospital treatment after deliberate self-harm.

This study was approved by the Danish Data Protection Agency.

What are absolute and relative risks?

The absolute risk of suicide according to diagnostic group is shown in Table 1. Among men, suicide risk was highest in bipolar disorder 7. The estimate of the suicide risk for men with anorexia is based on small numbers of cases. The cumulative incidence of suicide by time since the first psychiatric contact for each of the disorders investigated is shown in the Figure for men and women. The steepest increase in suicide incidence occurs during the first years after first contact. The cumulative incidences of suicide were virtually independent of age at onset of the different mental disorders data not shown.

In Table 2 , the cumulative incidence of suicide is presented for patients who had a diagnosis of a substance abuse disorder and a different additional mental disorders during the same contact or at different times. In all diagnostic groups, comorbidity with substance abuse disorder increased the cumulative incidence of suicide except among men with schizophrenia.

In Table 3 , the cumulative incidence of suicide is presented for patients who had a diagnosis of a unipolar affective disorder and a different additional mental disorder. For all mental disorders, comorbid occurrence of unipolar affective disorder increased the cumulative incidence of suicide. In Table 4 , the cumulative incidence for patients who had attempted suicide at least once is presented in different diagnostic groups among men and women. Overall, across all diagnostic groups, deliberate self-harm doubled the risk. The highest cumulative incidence of suicide was found among men with bipolar disorder and deliberate self-harm To our knowledge, this study has the hitherto largest sample and includes a long-term follow-up of a complete national sample from 15 to 51 years of age.

For both sexes, comorbid occurrence of substance abuse and unipolar affective disorders increased the absolute suicide risk, and co-occurrence of deliberate self-harm generally doubled the risk in each diagnostic group. The suicide risk increased steeply during the first few years after first contact with psychiatric services. Although the absolute suicide risks identified in this study are high, they are clearly lower than the often-cited figures reported by Guze and Robins 8 and Miles.

Estimates of the cumulative incidences in the literature have often ignored the fact that people may emigrate or die of other causes. The strengths of this study are the large and representative number of cases investigated, the long follow-up, and the fact that we accounted for emigration and death from other causes. The findings in our study are in agreement with the meta-analysis performed by Bostwick and Pankratz 12 and Palmer et al, 13 partly because Danish register-based studies contributed a large proportion of the patients and person-years included in their analyses.

Our study population includes all the Danish patients included in the meta-analyses; in our study, they were followed up longer than in previous studies. There are some limitations in a register-based study compared with a population-based survey. The study population includes only persons who have received some kind of treatment in psychiatric treatment facilities, and outpatient treatment was recorded only since However, most other studies have the same limitations. Another limitation is that we were able to identify incident cases of mental illness only among people born in or later and to follow up these individuals until , that is, people who had received a diagnosis of a mental illness before 51 years of age.

We can only speculate whether the absolute risks reported are applicable to people with later onset of a mental disorder. Based on our material, we cannot estimate lifetime risk because the cohort was followed up until, at most, 51 years of age. Also, because the design of the study exploits the advantages of including the longest possible historical period, there is a risk that changes in suicide risk occurred during the period investigated. Prior investigations have previously demonstrated that suicide rates for patients with schizophrenia, 26 affective disorder, and substance abuse 27 decreased and can be influenced by a range of conditions related to the treatment, as well as to other factors, such as availability of dangerous means.

The number of persons with bipolar disorder in our sample is much lower than the number of cases of schizophrenia. The explanation for the smaller figures is that many cases classified as bipolar II disorder in DSM terms will not be classified as bipolar disorders in ICD-8 and ICD and also that the incidence of bipolar disorder peaks at a later age 28 compared with schizophrenia. All persons in this study were classified according to the clinical diagnosis given at first contact with mental health services after 15 years of age.

Diagnostic switch between, for instance, schizophrenialike disorder and schizophrenia or a switch between unipolar affective disorder and bipolar disorder is therefore not taken into account. Theoretically, persons who later switched from one group to another could have a different risk than those who remained in the same group, thereby artificially leveling out differences between diagnostic groups. However, diagnostic switch cannot be taken into account without introducing survival bias healthy- worker effect.

Large prospective studies of first-onset cases with a long follow-up, such as the present study and the recent British year follow-up of first-episode psychosis cases, 30 provide good estimates of suicide risk. However, an inherent problem with such studies is that, by the time the results become available, the risk for new patients with first-episode psychosis may have changed because of changes in treatment and other factors. We did find higher figures than Dutta et al 5 , 30 in their study of patients with first-episode psychosis, which can be partly explained by differences between the 2 countries in classification of suicide, with higher suicide rates in Denmark.

It is a limitation that the data are only available from Denmark, which might limit generalization of our findings to other countries. In the s, Denmark had extraordinarily high suicide rates, most likely because of a large number of suicides with barbiturates. Despite these limitations, it is beyond doubt that the risk of suicide is high in all the investigated mental disorders, and suicide preventive measures should be a mandatory part of treatment programs, not only for affective disorders but also for schizophrenia and related disorders, for substance abuse, and for anorexia.

In addition, as underlined in recent findings from a large Swedish study, 35 attempted suicide should be considered a very important risk factor among patients with different mental disorders. The fact that the steepest increase in suicide risk occurs during the initial years after first contact with mental health services can serve as an argument for intensive early-intervention services.

By establishing closer contact and closer monitoring of symptoms, we hope that such services can reduce suicide risk in this high-risk period and thereby ensure that the long-term risk of suicide may be influenced positively. Submitted for Publication: January 24, ; final revision received April 10, ; accepted May 20, Author Contributions: All authors had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Role of the Sponsors: The funding organization had no influence on the design or conduct of the study. All Rights Reserved. Download PDF Comment. View Large Download. Table 1. Table 2. Table 3. Table 4. Psychiatric illness and risk factors for suicide in Denmark. Suicide risk in relation to psychiatric hospitalization: evidence based on longitudinal registers.

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Suicide as an outcome for mental disorders: a meta-analysis. Br J Psychiatry. Mental disorders and suicide prevention. Psychiatry Clin Neurosci. Reassessing the long-term risk of suicide after a first episode of psychosis. Schizophrenics kill themselves too: a review of risk factors for suicide.

Schizophr Bull.

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Conditions predisposing to suicide: a review. J Nerv Ment Dis. Suicide and primary affective disorders. Down-rating lifetime suicide risk in major depression. Acta Psychiatr Scand. Lifetime suicide risk in major depression: sex and age determinants. J Affect Disord. Affective disorders and suicide risk: a reexamination. Am J Psychiatry. The lifetime risk of suicide in schizophrenia: a reexamination. Lifetime risk of suicide for affective disorder, alcoholism and schizophrenia. Statistical Models Based on Counting Processes.


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Corrected ed. The Danish Civil Registration System: a cohort of eight million persons. Dan Med Bull. The Danish Registers of Causes of Death.


  1. Lifetime risk.
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  5. The Danish Psychiatric Central Register. World Health Organization. Copenhagen: Danish National Board of Health; Copenhagen: Munksgaard Danmark; The Danish National Hospital Register: a valuable source of data for modern health sciences. Frequent change of residence and risk of attempted and completed suicide among children and adolescents. Youth suicide attempts and the dose-response relationship to parental risk factors: a population-based study.

    Psychol Med. No evidence of time trends in the urban-rural differences in schizophrenia risk among five million people born in Denmark from to SAS macros for estimation of the cumulative incidence functions based on a Cox regression model for competing risks survival data. Comput Methods Programs Biomed. Change in suicide rates for patients with schizophrenia in Denmark, nested case-control study. Trends in suicide risk associated with hospitalized psychiatric illness: a case-control study based on Danish longitudinal registers.

    J Clin Psychiatry. A comparison of selected risk factors for unipolar depressive disorder, bipolar affective disorder, schizoaffective disorder, and schizophrenia from a Danish population-based cohort. Young males have a higher risk of developing schizophrenia: a Danish register study. Early risk factors for suicide in an epidemiological first episode psychosis cohort.

    Schizophr Res. Prevention of suicide and attempted suicide in Denmark: epidemiological studies of suicide and intervention studies in selected risk groups. The comparability of suicide rates. Restrictions in means for suicide: an effective tool in preventing suicide: the Danish experience. Rose 7 called attention years ago to the fact that the baseline risk of individuals participating in primary prevention trials was less than that of patients recruited in secondary prevention trials.

    This explains to a great extent why the benefit of the intervention is usually smaller in primary prevention trials than in secondary prevention trials. In fact, this principle must be considered before making any recommendations about prevention on a large scale..

    Various authors have demonstrated the advantages of presenting the results of studies of therapeutic effectiveness as the absolute reduction of risk ARR or NNT instead of the relative reduction of risk RRR , since RRR does not take the baseline level of risk of the subjects into consideration, as was commented above.

    This can be easily verified by comparing the same treatment in two situations with different levels of risk: moderate and mild arterial hypertension AHT. ARR simply expresses the benefit specifically attributable to the therapeutic intervention. On the other hand, as its name indicates, NNT is an index derived from the previous concept, which estimates how many patients must undergo the intervention proposed to avoid an episode.

    Laupacis et al 8 have calculated the individual benefits NNT of treating various cardiovascular conditions, comparing different factors and cardiovascular diseases Table An additional advantage of the NNT index is the possibility of applying it in an individualized way to any patient with any level of risk, whether greater or smaller than that of the patients included in the clinical trial of reference.

    For example, imagine that we have calculated that a patient has approximately one-half of the risk of the patients in the reference trial using a risk equation. This adjustment can also be made for factors like, for example, follow-up time, which allows therapeutic regimens of different duration to be compared.. The NNT can also be used to calculate the risk-benefit ratio of a treatment or as guidance to choose between several therapeutic alternatives.

    For example, consider any situation in which there are two treatment options, both of which produce the same results but are of different utility for the patient. An area of research of special interest at present is the treatment of medical information by clinicians and its influence on decision making. Recent studies, such as the one mentioned above, demonstrate consistently that the degree of enthusiasm of physicians with certain preventive treatments, such as AHT, depends fundamentally on how the results of the most relevant trials published are presented..

    Similar studies made with patients have demonstrated that the patients, like the physicians, were more inclined to accept the proposed treatment when the information on its potential benefit was presented as RRR. The authors concluded that the idea that many patients have of preventive treatment is determined by the way in which it is presented.

    These results indicate that many patients might not accept treatment even if the findings of published trials were presented in a clear and comprehensible way by physicians. In fact, communication of the potential effects beneficial and harmful of treatment to patients has special importance, particularly in primary prevention, where subjects are usually symptomatic and the benefits, if there are any, can only be expected in the long term.

    There are no studies in which, after informing patients about the potential benefits and drawbacks of the intervention, the probability of acceptance is measured in relation to the way in which this information is presented RRR, ARR or NNT. In addition, it is necessary to incorporate results that have not been considered much to date and have only been recently incorporated in trials, such as measurements of the quality of life..

    Finally, it would be very interesting to know if the active participation of patients in the process of therapeutic decision-making produces a benefit increased satisfaction, better quality of life, etc. To date, only testimonial evidence sustains the hypothesis that the active participation of patients in therapeutic decision-making can improve the clinical results of intervention. On the other hand, there is fear that this participation can negatively affect the doctor-patient relation.. See article. Correspondence: Dr. Hospital Universitario de la Princesa.

    E-mail: rgsanchez hup.

    Studying Studies: Part I - relative risk vs. absolute risk - Peter Attia

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    Calculating absolute risk and relative risk

    Article information. TABLE 1. Benefits of treating five cardiovascular problems. Number of patients needed to treat NNT. That is to say that to make a correct therapeutic decision it is not enough to know that the intervention has a beneficial effect, it is also necessary to know the magnitude of this effect. In fact, this principle must be considered before making any recommendations about prevention on a large scale. Laupacis et al 8 have calculated the individual benefits NNT of treating various cardiovascular conditions, comparing different factors and cardiovascular diseases Table 1.

    Rev Esp Cardiol, 55 , pp. Measured enthusiasm: does the method of reporting trial results alter perceptions of therapeutic effectiveness?. Ann Intern Med, , pp.