Iain K. Crombie

When can odds ratios mislead

Odds ratios are a common measure of the size of an effect and may be reported in case-control studies, cohort studies, or clinical trials. Increasingly, they are also used to report the findings from systematic reviews and meta-analyses. Odds ratios are hard to comprehend directly and are usually interpreted as being equivalent to the relative risk. Unfortunately, there is a recognised problem that odds ratios do not approximate well to the relative risk when the initial risk (that is, the prevalence of the outcome of interest) is high. 1 2 Thus there is a danger that if odds ratios are interpreted as though they were relative risks then they may mislead. The advice given in many texts is unusually coy on the matter. For example: “The odds ratio is approximately the same as the relative risk if the outcome of interest is rare. For common events, however, they can be quite different.”3 How close is “approximately the same,” how uncommon does an event have to be to qualify as “rare,” and how different is “quite different”? #### Summary points If the odds ratio is interpreted as a relative risk it will always overstate any effect size: the odds ratio is smaller than the relative risk for odds ratios of less than one, and bigger than the relative risk for odds ratios of greater than one The extent of overstatement increases as both the initial risk increases and the odds ratio departs from unity However, serious divergence between the odds ratio and the relative risk occurs only with large effects on groups at high initial risk. Therefore qualitative judgments based on interpreting odds ratios as though they were relative risks are unlikely to be seriously in error In studies which show reductions in risk (odds ratios of less than one), the odds ratio …

Efficacy and tolerability of tricyclic antidepressants and SSRIs compared with placebo for treatment of depression in primary care: a meta-analysis.

PURPOSE Depression is common in primary care. There are no systematic reviews of depression treatment comparing antidepressants with placebo; hence, we do not know whether these medications are effective in primary care. METHODS We searched the Cochrane Collaboration Depression, Anxiety and Neurosis Group register of controlled trials, MEDLINE, International Pharmaceutical abstracts, PsycINFO, and EMBASE. Abstracts of potential studies were reviewed independently by 2 authors. Studies needed to include randomized controlled trials of either a tricyclic antidepressant (TCA) or selective serotonin reuptake inhibitor (SSRI), or both, and placebo in a primary care setting. The data and quality of the studies were extracted and assessed by 2 authors blind to the other’s choice. Disagreements were resolved by discussion. The main outcome measures were the standardized mean difference and weighted mean difference of the final mean depression scores, the relative risk of improvement, and the number withdrawing because of side effects. Pooling of results was done using Review Manager 4.2.2. RESULTS There were 10 studies in which TCAs were compared with placebo, 3 in which SSRIs were compared with placebo, and 2 with both compared with placebo. One half of the studies were of low methodological quality, and nearly all studies were of short duration, typically 6 to 8 weeks. Pooled estimates of efficacy data showed a relative risk of 1.26 (95% CI, 1.12–1.42) for improvement with TCAs compared with placebo; For SSRIs, relative risk was 1.37 (95% CI, 1.21–1.55). Most patients, 56% to 60%, responded well to active treatment compared with 42% to 47% for placebo. The number needed to treat for TCAs was about 4, and for SSRIs it was 6. The numbers needed to harm (for withdrawal caused by side effects) ranged from 5 to 11 for TCAs and 21 to 94 for SSRIs. Low-dose (100 mg or 75 mg) as well as high-dose TCAs were effective. CONCLUSION This systematic review is the first comparing antidepressants with placebo for treatment of depression in primary care. Both TCAs and SSRIs are effective. This review is also the first to show that low-dose TCAs are effective in primary care. Prescribing antidepressants in primary care is a more effective clinical activity than prescribing placebo.

Cut and thrust : antecedent surgery and trauma among patients attending a chronic pain clinic

&NA; Surgery and trauma are recognised as important causes of chronic pain, although their overall contribution has not been systematically studied. This paper reports on the contribution of surgery and trauma to chronic pain among 5130 patients attending 10 outpatient clinics located throughout North Britain. Surgery contributed to pain in 22.5% of patients, and was particularly associated with the development of pain in the abdomen and with anal, perineal and genital pain. Trauma was a cause of pain in 18.7% of patients, and was most common in pain in the upper limb, the spine and the lower limb. Patients with chronic pain associated with trauma are on average younger than those with chronic post‐surgical pain. Further, and unusually for pain conditions, the trauma patients show an excess of males over females. These findings indicate that it can be unhelpful for pain classification systems to combine surgery and trauma in a single category. The results also point to areas for potentially fruitful research into the aetiology of chronic pain. In particular, studies are needed to identify the operative procedures associated with the development of pain so that preventive measures can be implemented.

Reviewing audit: barriers and facilitating factors for effective clinical audit

Objective—To review the literature on the benefits and disadvantages of clinical and medical audit, and to assess the main facilitators and barriers to conducting the audit process. Design—A comprehensive literature review was undertaken through a thorough review of Medline and CINAHL databases using the keywords of “audit”, “audit of audits”, and “evaluation of audits” and a handsearch of the indexes of relevant journals for key papers. Results—Findings from 93 publications were reviewed. These ranged from single case studies of individual audit projects through retrospective reviews of departmental audit programmes to studies of interface projects between primary and secondary care. The studies reviewed incorporated the experiences of a wide variety of clinicians, from medical consultants to professionals allied to medicine and from those involved in unidisciplinary and multidisciplinary ventures. Perceived benefits of audit included improved communication among colleagues and other professional groups, improved patient care, increased professional satisfaction, and better administration. Some disadvantages of audit were perceived as diminished clinical ownership, fear of litigation, hierarchical and territorial suspicions, and professional isolation. The main barriers to clinical audit can be classified under five main headings. These are lack of resources, lack of expertise or advice in project design and analysis, problems between groups and group members, lack of an overall plan for audit, and organisational impediments. Key facilitating factors to audit were also identified: they included modern medical records systems, effective training, dedicated staff, protected time, structured programmes, and a shared dialogue between purchasers and providers. Conclusions—Clinical audit can be a valuable assistance to any programme which aims to improve the quality of health care and its delivery. Yet without a coherent strategy aimed at nurturing effective audits, valuable opportunities will be lost. Paying careful attention to the professional attitudes highlighted in this review may help audit to deliver on some of its promise. (Quality in Health Care 2000;9:23–36)

Efficacy and tolerability of selective serotonin reuptake inhibitors compared with tricyclic antidepressants in depression treated in primary care: systematic review and meta-analysis

Abstract Objective: To compare the efficacy and tolerability of tricyclic antidepressants with selective serotonin reuptake inhibitors in depression in primary care. Design: Systematic review and meta-analysis of randomised controlled trials. Data sources: Register of the Cochrane Collaborations depression, anxiety, and neurosis group. Reference lists of initial studies and other relevant review papers. Selected authors and experts. Selection of studies: Studies had to meet minimum requirements on: adequacy of sample size, adequate allocation concealment, clear description of treatment, representative source of subjects, use of diagnostic criteria or clear specification of inclusion criteria, details regarding number and reasons for withdrawal by group, and outcome measures described clearly or use of validated instruments. Main outcome measures: Standardised mean difference of final mean depression scores and relative risk of response when using the clinical global impression score. Relative risk of withdrawing from treatment at any time, and the number withdrawing due to side effects. Results: 11 studies (2951 participants) compared a selective serotonin reuptake inhibitor with a tricyclic antidepressant. Efficacy between selective serotonin reuptake inhibitors and tricyclics did not differ significantly (standardised weighted mean difference, fixed effects 0.07, 95% confidence interval −0.02 to 0.15; z=1.59, P<0.11). Significantly more patients receiving a tricyclic withdrew from treatment (relative risk 0.78, 95% confidence interval 0.68 to 0.90; z=3.37, P<0.0007) and withdrew specifically because of side effects (0.73, 0.60 to 0.88; z=3.24, P<0.001). Most studies included were small and supported by commercial funding. Many studies were of low methodological quality or did not present adequate data for analysis, or both, and were of short duration, typically six to eight weeks. Conclusion: The evidence on the relative efficacy of selective serotonin reuptake inhibitors and tricyclic antidepressants in primary care is sparse and of variable quality. The study setting is likely to be an important factor in assessing the efficacy and tolerability of treatment with antidepressant drugs. What is already known on this topic Previous meta-analyses have included comparatively large numbers of secondary care based studies that indicate no significant differences in efficacy between selective serotonin reuptake inhibitors and tricyclics Previous meta-analyses are conflicting regarding the relative tolerability between selective serotonin reuptake inhibitors and tricyclics, but do suggest a small but significant difference in favour of selective serotonin reuptake inhibitors Such meta-analyses show notable heterogeneity What this study adds Selective serotonin reuptake inhibitors are better tolerated than tricyclics by primary care patients and may be better tolerated by primary care patients than secondary care patients Study setting seems to be important and should be considered before licences are given to specific antidepressants Although there are limited high quality data, available evidence shows that the most commonly prescribed classes of antidepressants in primary care (selective serotonin reuptake inhibitors and tricyclics) are equally effective in the short term for primary care patients, but the literature has many gaps

Control of blood pressure in Scotland: the rule of halves.

OBJECTIVE--Audit of detection, treatment, and control of hypertension in adults in Scotland. DESIGN--Cross sectional survey with random population sampling. SETTING--General practice centres in 22 Scottish districts. SUBJECTS--5123 Men and 5236 women aged 40-59 in the Scottish heart health study, randomly selected from 22 districts throughout Scotland, of whom 1262 men and 1061 women had hypertension (defined as receiving antihypertensive treatment or with blood pressure above defined cut off points). MAIN OUTCOME MEASURE--Hypertension (assessed by standardised recording, questionnaire on diagnosis, and antihypertensive drug treatment) according to criteria of the World Health Organisation (receiving antihypertensive treatment or blood pressure greater than or equal to 160/95 mm Hg, or both) and to modified criteria of the British Hypertension Society. RESULTS--In half the men with blood pressure greater than or equal to 160/95 mm Hg hypertension was undetected (670/1262, 53%), in half of those in whom it had been detected it was untreated (250/592, 42%), and in half of those receiving treatment it was not controlled (172/342, 50%). In women the numbers were: 486/1061, 46%; 188/575, 33%; and 155/387, 40% respectively. Assessment of blood pressure according to the British Hypertension Societys recommendations showed an improvement, but in only a quarter of men and 42% of women was hypertension detected and treated satisfactorily (142/561, 215/514 respectively). IMPLICATIONS--The detection and control of hypertension in Scotland is unsatisfactory, affecting management of this and other conditions, such as high blood cholesterol concentration, whose measurement is opportunistic and selective and depends on recognition of other risk factors.

Advising parents of asthmatic children on passive smoking: randomised controlled trial

Abstract Objective: To investigate whether parents of asthmatic children would stop smoking or alter their smoking habits to protect their children from environmental tobacco smoke. Design: Randomised controlled trial. Setting: Tayside and Fife, Scotland. Participants: 501 families with an asthmatic child aged 2-12 years living with a parent who smoked. Intervention: Parents were told about the impact of passive smoking on asthma and were advised to stop smoking or change their smoking habits to protect their childs health. Main outcome measures: Salivary cotinine concentrations in children, and changes in reported smoking habits of the parents 1 year after the intervention. Results: At the second visit, about 1 year after the baseline visit, a small decrease in salivary cotinine concentrations was found in both groups of children: the mean decrease in the intervention group (0.70 ng/ml) was slightly smaller than that of the control group (0.88 ng/ml), but the net difference of 0.19 ng/ml had a wide 95% confidence interval (−0.86 to 0.48). Overall, 98% of parents in both groups still smoked at follow up. However, there was a non-significant tendency for parents in the intervention group to report smoking more at follow up and to having a reduced desire to stop smoking. Conclusions: A brief intervention to advise parents of asthmatic children about the risks from passive smoking was ineffective in reducing their childrens exposure to environmental tobacco smoke. The intervention may have made some parents less inclined to stop smoking. If a clinician believes that a childs health is being affected by parental smoking, the parents smoking needs to be addressed as a separate issue from the childs health. Key messages Many asthmatic children are exposed to high levels of environmental tobacco smoke A brief intervention informing parents of asthmatic children on the harmful effects of passive smoking did not lead to a reduction in exposure of their children to tobacco smoke Low rates of smoking cessation were found in both the intervention group and the control group Some parents may have been less inclined to stop smoking after the intervention Brief interventions requesting smokers to stop for another persons health seem ineffective

Urinary electrolyte excretion, alcohol consumption, and blood pressure in the Scottish heart health study

As part of a study of risk factors for coronary heart disease 24 hour urine collections were obtained from 7354 men and women aged 40-59 selected at random from 22 districts throughout Scotland (Scottish heart health study). The mean of two standardised measurements of blood pressure was related to the reported consumption of alcohol and measurements of height, weight, pulse rate, and electrolyte excretion. Several significant correlations were found with both systolic and diastolic pressure, but only the coefficients for age, body mass index, and pulse rate were greater than 0.1. Alcohol consumption showed a weak positive correlation with blood pressure in men. Sodium excretion showed a weak positive correlation with blood pressure in both sexes, and potassium excretion showed weak negative correlations. In multiple regression analysis age, pulse rate, body mass index, alcohol consumption, and potassium excretion had significant independent effects but sodium excretion did not. Although measuring blood pressure twice on one occasion and 24 hour urinary sodium excretion only once may have weakened any potential correlation, the most likely explantation of these results is that the relation between sodium and blood pressure in the population is weak and that potassium and alcohol are of greater importance.

Assessing the quality of care

Measuring well supported processes may be more enlightening than monitoring outcomes Everyone wants information on clinical outcomes.1 These measures have an intuitive appeal: high quality care should be reflected by good outcomes. Therefore, poorer outcomes should indicate deficiencies in care, including missed opportunities or wasted resources. The hope is that data on outcomes will provide a barometer for health care, indicating the effectiveness and efficiency of service delivery. Many purchasers are pushing to include outcomes criteria in their contracts as a means of assessing effectiveness. In clinical audit, measurement of outcome is generally considered superior to audits that simply assess the process of care.2 But perhaps this emphasis on outcomes is being overplayed. Are outcomes data always so enlightening? Outcome measures have a major weakness: interpretation. Suppose a hospital reported that patients admitted with coronary heart disease in 1994 had a 30 day mortality of 25%. This can be interpreted only by comparison with …

Weight loss interventions in young people (18 to 25 year olds): a systematic review.

This systematic review assesses weight loss interventions in young adults (18–25 years), who are vulnerable to weight gain. This age group experience critical life course points (leaving home for higher studies or job, pregnancy, cohabitation) and develop/establish lifestyle and behavioural patterns making this an opportune intervention period. Medline, Embase, Cinahl, PsychINFO and Cochrane Library were searched (1980 to March 2008). All trials and cohort studies with control groups that assessed weight loss interventions in this specific age group were included finally identifying 14 studies. Before and after comparison of behavioural/motivational interventions (−2.40 kg; 95% CI −5.4 to 0.6) and combination interventions (−2.96; 95% CI −4.4 to −1.5) consistently showed weight loss. Behavioural/motivational interventions increased self‐efficacy, the desire to control weight, boosted self‐esteem, and increased satisfaction with body areas and appearance. Interventions also showed improvements in HDL cholesterol, insulin, glucose and maximum oxygen uptake. However, recruitment to participation in interventions was a barrier for this age group with small sample sizes and short‐term interventions. There may be gender differences in preference to participation in certain type of interventions. Further research to understand attitudes towards healthy lifestyle and preferences of interventions is needed to develop suitable interventions for this vulnerable age group.