Associations between psychiatric disorders and cancer incidence are inconsistent, with studies reporting cancer rates in psychiatric patients that are higher, similar, or lower than the general population. Exploration of these associations is complicated by difficulties in establishing the timing of onset of psychiatric disorders and cancer, and the associated possibility of reverse causality. Some studies have dealt with this problem by excluding patients with cancers pre-dating their psychiatric illness; others have not considered the issue.
We examined associations between psychiatric hospitalization and cancer incidence in a cohort of 1,165,039 Swedish men, and explored the impact of different analytical strategies on these associations using real and simulated data.
Relative to men without psychiatric hospitalization, we observed consistent increases in smoking-related cancers in those with psychiatric hospitalizations, regardless of analytical approach (for example, hazard ratio (95% confidence interval): 1.73 (1.52, 1.96)). However, associations with nonsmoking-related cancers were highly dependent on analytical strategy. In analyses based on the full cohort, we observed no association or a modest increase in cancer incidence in those with psychiatric hospitalizations (1.14 (1.07, 1.22)). In contrast, analyses excluding men whose cancer predated their psychiatric hospitalizations, resulted in a reduction in future cancer incidence in psychiatric patients (0.72; 0.67, 0.78). Results from simulated data suggest that even modest exclusions of this type can lead to strong artefactual associations.
Psychiatric disorder-cancer incidence associations are complex and influenced by analytical strategy. A greater understanding of the temporal relationship between psychiatric disorder and cancer incidence is required.
Mental disorders have been associated with increased mortality, but the evidence is primarily based on hospital admissions for psychoses. The underlying mechanisms are unclear.
To investigate whether the risks of death associated with mental disorders diagnosed in young men are similar to those associated with admission for these disorders, and to examine the role of confounding or mediating factors.
Prospective cohort study in which mental disorders were assessed by psychiatric interview during a medical examination on conscription for military service at a mean age of 18.3 years and data on psychiatric hospital admissions and mortality during a mean 22.6 years of follow-up were obtained from national registers.
1,095,338 men conscripted between 1969 and 1994.
Main outcome measure
All-cause mortality according to diagnoses of schizophrenia, other non-affective psychoses, bipolar or depressive disorders, neurotic/adjustment disorders, personality disorders, alcohol-related or other substance use disorders at conscription and on hospital admission.
Diagnosis of mental disorder at conscription or on hospital admission was associated with increased mortality. Age-adjusted hazard ratios (95% confidence intervals) according to diagnoses at conscription ranged from 1.81 (1.54, 2.10) (depressive disorders) to 5.55 (1.79, 17.2) (bipolar disorders). The equivalent figures according to hospital diagnoses ranged from 5.46 (5.06, 5.89) (neurotic/adjustment disorders) to 11.2 (10.4, 12.0) (other substance use disorders) in men born 1951-8 and increased in men born later. Adjustment for early-life socioeconomic status, body mass index and blood pressure had little effect on these associations, but they were partially attenuated by adjustment for smoking, alcohol intake, intelligence, education and late-life socioeconomic position. These associations were not primarily due to deaths from suicide.
The increased risk of premature death associated with mental disorder is not confined to those whose illness is severe enough for hospitalisation or to those with psychotic or substance-use disorders.
There is growing evidence of an inverse association between intelligence (IQ) and unintentional injuries.
Analyses are based on a cohort of 1,109,475 Swedish men with IQ measured in early adulthood. Men were followed-up for an average 24 years and hospital admissions for unintentional injury were recorded.
198,133 (17.9%) men had at least one hospital admission for any unintentional injury during follow-up. The most common cause of unintentional injury was falling, followed by road accidents, poisoning, fire and drowning. In addition, 14,637 (1.3%) men had at least one admission for complications of medical care. After adjusting for confounding variables, lower IQ scores were associated with an elevated risk of any unintentional injury (Hazard ratio (95% confidence interval) per standard deviation decrease in IQ: 1.15 (1.14, 1.15)), and of cause-specific injuries other than drowning (poisoning (1.53 (1.49, 1.57)), fire (1.36 (1.31, 1.41)), road traffic accidents (1.25 (1.23, 1.26)), medical complications (1.20 (1.18, 1.22)), and falling (1.17 (1.16, 1.18)). These gradients were stepwise across the full IQ range.
Low IQ scores in early adulthood were associated with a subsequently increased risk of unintentional injury. A greater understanding of mechanisms underlying these associations may provide opportunities and strategies for prevention.
IQ; injury; socioeconomic status; cohort
Adult height, a marker of early-life environment, has been sporadically associated with suicide risk. We have examined adult height and attempted suicide risk in a cohort of 1,102,293 Swedish men and, in fully-adjusted analyses, found decreasing stepwise associations between height and attempted suicides by any means and most specific means.
Attempted suicide; Height; Cohort
Lower IQ individuals have an increased risk of psychological disorders, mental health problems, and suicide; similarly, children with low IQ scores are more likely to have behavioural, emotional and anxiety disorders. However, very little is known about the impact of parental IQ on the mental health outcomes of their children.
To determine whether maternal and paternal IQ score is associated with offspring conduct, emotional and attention scores.
Members of 1958 National Child Development Study and their offspring. Of 2,984 parent-offspring pairs, with non-adopted children aged 4+ years, 2,202 pairs had complete data on all variables of interest and were included in the analyses.
Offspring conduct, emotional and attention scores based on Behavioural Problems Index for children aged 4-6 years or the Rutter A scale for children aged 7 and over.
There was little evidence of any association of parental IQ with conduct or emotional problems in younger (aged 4-6) children. However, among children aged 7+, there was strong evidence from age- and sex-adjusted models to support a decrease in conduct, emotional and attention problems in those whose parents had higher IQ scores. These associations were linear across the full IQ range. Individual adjustments for socioeconomic status and child’s own IQ had limited impact while adjustments for Home Observation for Measurement of the Environment (HOME) scores and parental malaise attenuated associations with mother’s IQ but, again, had little impact on associations with father’s IQ. Strong associations were no longer evident in models that simultaneously adjusted for all four potential mediating variables.
Children whose parents score poorly on IQ tests may have an increased risk of conduct, emotional and attention problems. Home environment, parental malaise, and child’s own IQ may have a role in explaining these associations.
There is growing evidence of an association between low intelligence (IQ) and increased risk of assault. However, previous studies are relatively small, do not adjust for socioeconomic status, and have not examined method-specific assaults.
Cox proportional hazards regression was used to explore IQ associations with assault by any means and by four specific methods in a large prospective cohort of 1,120,988 Swedish men. Study members had IQ measured in early adulthood and were well characterised for socioeconomic status in childhood and adulthood. Men were followed-up for an average of 24 years and hospital admissions for injury due to assault were recorded.
16,512 (1.5%) men had at least one hospital admission for injury due to assault by any means during follow-up. The most common assault was during a fight (N=13,144), followed by stabbing (N=1,211), blunt instrument (N=352), and firearms assaults (N=51). After adjusting for confounding variables, lower IQ scores were associated with an elevated risk of hospitalisation for assaults by any means (Hazard ratio (95% confidence interval) per standard deviation decrease in IQ: 1.51 (1.49, 1.54)), and for each of the cause-specific assaults (fight: 1.48 (1.45, 1.51); stabbing: 1.68 (1.58, 1.79); blunt instrument: 1.65 (1.47, 1.85); and firearms: 1.34 (1.00, 1.80)). These gradients were stepwise across the full IQ range.
Low IQ scores in early adulthood were associated with a subsequently increased risk of assault. A greater understanding of mechanisms underlying these associations may provide opportunities and strategies for prevention.
IQ; assault; socioeconomic status; cohort
Individuals scoring poorly on tests of intelligence (IQ) have been reported as having increased risk of morbidity, premature mortality, and risk factors such as obesity, high blood pressure, poor diet, alcohol and cigarette consumption. Very little is known about the impact of parental IQ on the health and health behaviours of their offspring.
We explored associations of maternal and paternal IQ scores with offspring television viewing, injuries, hospitalisations, long standing illness, height and BMI at ages 4 to 18 using data from the National Child Development Study (1958 birth cohort).
Data were available for 1,446 mother-offspring and 822 father-offspring pairs. After adjusting for potential confounding/mediating factors, the children of higher IQ parents were less likely to watch TV (odds ratio (95% confidence interval) for watching 3+ vs. <3 hours per week associated with a standard deviation increase in maternal or paternal IQ: 0.75 (0.64, 0.88) or 0.78 (0.64, 0.95) respectively) and less likely to have one or more injuries requiring hospitalisation (0.77 (0.66, 0.90) or 0.72 (0.56, 0.91) respectively for maternal or paternal IQ).
Children whose parents have low IQ scores may have poorer selected health and health behaviours. Health education might usefully be targeted at these families.
Intelligence; Life course; Birth cohort; Trans-generational
Socioeconomic differentials in mortality are increasing in many industrialised countries.
This study aims to examine the role of behaviours (smoking, alcohol, exercise, and diet) in explaining socioeconomic differentials in mortality and whether this varies over the life course, between cohorts and by gender.
Analysis of two representative population cohorts of men and women, born in the 1950s and 1930s, were performed. Health behaviours were assessed on five occasions over 20 years.
Health behaviours explained a substantial part of the socioeconomic differentials in mortality. Cumulative behaviours and those that were more strongly associated with socioeconomic status had the greatest impact. For example, in the 1950s cohort, the age-sex adjusted hazard ratio comparing respondents with manual versus non-manual occupational status was 1.80 (1.25, 2.58); adjustment for cumulative smoking over 20 years attenuated the association by 49 %, diet by 43 %, drinking by 13 % and inactivity by only 1%.
Health behaviours have an important role in explaining socioeconomic differentials in mortality.
Mortality; Socioeconomic status; Health behaviours; Cohort
The adverse effects of advancing maternal age on offspring's health and development are well understood. Much less is known about the impact of paternal age.
We explored paternal age-offspring cognition associations in 772 participants from the West of Scotland Twenty-07 study. Offspring cognitive ability was assessed using Part 1 of the Alice Heim 4 (AH4) test of General Intelligence and by reaction time (RT).
There was no evidence of a parental age association with offspring RT. However, we observed an inverse U-shaped association between paternal age and offspring AH4 score with the lowest scores observed for the youngest and oldest fathers. Adjustment for parental education and socioeconomic status somewhat attenuated this association. Adjustment for number of, particularly older, siblings further reduced the scores of children of younger fathers and appeared to account for the lower offspring scores in the oldest paternal age group.
We observed a paternal age association with AH4 but not RT, a measure of cognition largely independent of social and educational experiences. Factors such as parental education, socioeconomic status and number of, particularly older, siblings may play an important role in accounting for paternal age-AH4 associations. Future studies should include parental intelligence.
An evaluation of progress with participatory approaches for improvement of health knowledge and health experiences of disadvantaged people in eight Districts of Eastern Nepal has been undertaken.
A random selection of Village Development Committees and households, within the eight Districts where participation and a Rights-based Approach had been promoted specifically by local NGOs were compared with similar villages and households in eight Districts where this approach had not been promoted. Information was sought by structured interview and observation by experienced enumerators from both groups of householders. Health knowledge and experiences were compared between the two sets of households. Adjustments were made for demographic confounders.
Complete data sets were available for 628 of the 640 households. Health knowledge and experiences were low for both sets of households. However, health knowledge and experiences were greater in the participatory households compared with the non-participatory households. These differences remained after adjustment for confounders.
The study was designed to evaluate progress with participatory processes delivered by non-governmental organisations over a five year period. Improvements in health knowledge and experiences of disadvantaged people were demonstrated in a consistent and robust manner where interventions had taken place.
Associations between body mass index (BMI) and attempted (nonfatal) suicide have recently been reported. However, the few existing studies are relatively small in scale, the majority cross-sectional, and results contradictory. The authors have explored BMI–attempted suicide associations in a large cohort of 1,133,019 Swedish men born between 1950 and 1976, with BMI measured in early adulthood. During a mean follow-up of 23.9 years, a total of 18,277 (1.6%) men had at least 1 hospital admission for attempted suicide. After adjustment for confounding factors, there was a stepwise, linear decrease in attempted suicide with increasing BMI across the full BMI range (per standard deviation increase in BMI, hazard ratio = 0.93, 95% confidence interval: 0.91, 0.94). Analyses excluding men with depression at baseline were essentially identical to those based on the complete cohort. In men free from depression at baseline, controlling for subsequent depression slightly attenuated the raised risk of attempted suicide, particularly in lower weight men. This study suggests that lower weight men have an increased risk of attempted suicide and that associations may extend into the “normal” BMI range.
body mass index; cohort studies; depression; social class; suicide, attempted
Objectives To explore associations between IQ measured in early adulthood and subsequent hospital admissions for attempted suicide and to explore the role of psychosis and examine associations of IQ with specific methods of attempted suicide.
Design Cohort study.
Participants 1 109 475 Swedish men with IQ measured in early adulthood followed up for an average 24 years.
Main outcome measures Hospital admission for attempted suicide.
Results 17 736 (1.6%) men had at least one hospital admission for attempted suicide by any means during follow-up. After adjustment for age and socioeconomic status, lower IQ scores were associated with an elevated risk of attempted suicide by any means (hazard ratio per standard deviation decrease in IQ=1.57, 95% confidence interval 1.54 to 1.60), with stepwise increases in risk across the full IQ range (P for trend<0.001). Similar associations were observed for all specific methods of attempted suicide. Separate analyses indicated that associations between IQ and attempted suicide were restricted to participants without psychosis and that IQ had no marked impact on risk of attempted suicide in those with psychosis.
Conclusions Low IQ scores in early adulthood were associated with a subsequently increased risk of attempted suicide in men free from psychosis. A greater understanding of the mechanisms underlying these associations may provide opportunities and strategies for prevention.
Falls are common and often preventable in older people. This short report describes substantial unmet need in relation to falls. Although falling, nearly falling, fear of falling, and activity restriction are common, many people do not seek assistance from healthcare professionals. Only 2% of those who had attended their general practioner (GP), a casualty department, or had been admitted to hospital after a fall were taking drugs to protect against osteoporosis. People who have fallen or are at a risk of falling need to be identified, and local policies and information regarding treatment for osteoporosis are needed.
The present review introduces nonparametric methods. Three of the more common nonparametric methods are described in detail, and the advantages and disadvantages of nonparametric versus parametric methods in general are discussed.
nonparametric methods; sign test; Wilcoxon signed rank test; Wilcoxon rank sum test
The present review introduces the commonly used t-test, used to compare a single mean with a hypothesized value, two means arising from paired data, or two means arising from unpaired data. The assumptions underlying these tests are also discussed.
comparison of two means; paired and unpaired data; t test
The present review introduces the notion of statistical power and the hazard of under-powered studies. The problem of how to calculate an ideal sample size is also discussed within the context of factors that affect power, and specific methods for the calculation of sample size are presented for two common scenarios, along with extensions to the simplest case.
statistical power; sample size
The present review introduces the general philosophy behind hypothesis (significance) testing and calculation of P values. Guidelines for the interpretation of P values are also provided in the context of a published example, along with some of the common pitfalls. Examples of specific statistical tests will be covered in future reviews.
hypothesis testing; null hypothesis; P value
The previous review in this series introduced the notion of data description and outlined some of the more common summary measures used to describe a dataset. However, a dataset is typically only of interest for the information it provides regarding the population from which it was drawn. The present review focuses on estimation of population values from a sample.
confidence interval; normal distribution; reference range; standard error
Statistics is increasingly used in all fields of medicine but is often poorly understood and incorrectly applied. Critical Care is therefore launching a series of articles aimed at providing a simple introduction or refresher to some of the more commonly used statistical tools and ideas. This series does not aim to be an exhaustive review of medical statistics but rather a starting point to inform readers and stimulate more thought and investigation as to the most appropriate statistical methods to use and the theory and assumptions behind them.
data analysis; medical statistics
The present review is the first in an ongoing guide to medical statistics, using specific examples from intensive care. The first step in any analysis is to describe and summarize the data. As well as becoming familiar with the data, this is also an opportunity to look for unusually high or low values (outliers), to check the assumptions required for statistical tests, and to decide the best way to categorize the data if this is necessary. In addition to tables and graphs, summary values are a convenient way to summarize large amounts of information. This review introduces some of these measures. It describes and gives examples of qualitative data (unordered and ordered) and quantitative data (discrete and continuous); how these types of data can be represented figuratively; the two important features of a quantitative dataset (location and variability); the measures of location (mean, median and mode); the measures of variability (range, interquartile range, standard deviation and variance); common distributions of clinical data; and simple transformations of positively skewed data.
interquartile range; mean; median; range; standard deviation; transformations; unimodal distributions
Objective and design
To relate UK national trends since 1950 in smoking, in smoking cessation, and in lung cancer to the contrasting results from two large case-control studies centred around 1950 and 1990.
Hospital patients under 75 years of age with and without lung cancer in 1950 and 1990, plus, in 1990, a matched sample of the local population: 1465 case-control pairs in the 1950 study, and 982 cases plus 3185 controls in the 1990 study.
Main outcome measures
Smoking prevalence and lung cancer.
For men in early middle age in the United Kingdom the prevalence of smoking halved between 1950 and 1990 but the death rate from lung cancer at ages 35-54 fell even more rapidly, indicating some reduction in the risk among continuing smokers. In contrast, women and older men who were still current smokers in 1990 were more likely than those in 1950 to have been persistent cigarette smokers throughout adult life and so had higher lung cancer rates than current smokers in 1950. The cumulative risk of death from lung cancer by age 75 (in the absence of other causes of death) rose from 6% at 1950 rates to 16% at 1990 rates in male cigarette smokers, and from 1% to 10% in female cigarette smokers. Among both men and women in 1990, however, the former smokers had only a fraction of the lung cancer rate of continuing smokers, and this fraction fell steeply with time since stopping. By 1990 cessation had almost halved the number of lung cancers that would have been expected if the former smokers had continued. For men who stopped at ages 60, 50, 40, and 30 the cumulative risks of lung cancer by age 75 were 10%, 6%, 3%, and 2%.
People who stop smoking, even well into middle age, avoid most of their subsequent risk of lung cancer, and stopping before middle age avoids more than 90% of the risk attributable to tobacco. Mortality in the near future and throughout the first half of the 21st century could be substantially reduced by current smokers giving up the habit. In contrast, the extent to which young people henceforth become persistent smokers will affect mortality rates chiefly in the middle or second half of the 21st century.
To investigate the association between suicide and area based measures of deprivation and social fragmentation.
633 parliamentary constituencies of Great Britain as defined in 1991.
Main outcome measures
Age and sex specific mortality rates for suicide and all other causes for 1981-92.
Mortality from suicide and all other causes increased with increasing Townsend deprivation score, social fragmentation score, and abstention from voting in all age and sex groups. Suicide mortality was most strongly related to social fragmentation, whereas deaths from other causes were more closely associated with Townsend score. Constituencies with absolute increases in social fragmentation and Townsend scores between 1981 and 1991 tended to have greater increases in suicide rates over the same period. The relation between change in social fragmentation and suicide was largely independent of Townsend score, whereas the association with Townsend score was generally reduced after adjustment for social fragmentation.
Suicide rates are more strongly associated with measures of social fragmentation than with poverty at a constituency level.
Key messagesPlace of residence may affect health, and mortality from most common diseases tends to be higher in areas characterised by low socioeconomic positionResearch dating back over 100 years suggests that social fragmentation may influencesuicideIn the 1980s and 1990s, parliamentary constituencies with high levels of social fragmentation had high rates of suicide, independent of deprivationConstituencies with the greatest increases in social fragmentation between 1981 and 1991 also had the greatest increases in suicide rates over the same periodAny targeting of suicide prevention may be more effective if aimed at socially fragmented rather than deprived areas