Alissa Beath

Guided by the research design: choosing the right statistical test

hoosing the right statistical test or model can be baffling for researchers, and if it is not conCducted correctly, the results from statistical analyses can be misleading. This article covers some common medical research designs, ranging from simple to more complicated, and provides an outline of which statistical test to apply in each instance. In these contexts, data are collected from a sample that is assumed to be representative of a wider population, and the conclusions drawn from the analyses apply to the wider population.

Factors Associated With Response to Placebo in Patients With Irritable Bowel Syndrome and Constipation

BACKGROUND & AIMS: A high proportion of patients with irritable bowel syndrome (IBS) respond to placebo in clinical trials (estimated at about 40%). We aimed to identify factors that contribute to the high placebo response rate using data from a placebo‐controlled trial of patients with IBS. METHODS: We performed a retrospective analysis of 599 women with IBS with constipation who were in the placebo group of a 12‐week, randomized, double‐blind, phase 3 trial of the experimental medication renzapride. Primary analyses evaluated frequency of abdominal pain in patients who received placebo, defined as ≥30% pain improvement from baseline for ≥6 of the 12 study weeks. We performed backward elimination regression with bootstrapping to identify factors associated with response to placebo. RESULTS: In the placebo group, 29.0% of the patients had an abdominal pain response. Factors associated with a response to placebo were baseline variation in abdominal pain (odds ratio [OR], 1.71), maximum baseline pain severity (OR, 1.34), and placebo response in study week 2 (OR, 2.23) or week 3 (OR, 3.69). Factors associated with lack of response to placebo were number of baseline complete spontaneous bowel movements (OR, 0.73; P = .019) and final baseline pain ratings (OR, 0.73; P < .001). CONCLUSIONS: We identified factors associated with a response in abdominal pain to placebo using original data from an IBS clinical trial. Baseline factors associated with the placebo response in women with IBS and constipation included variation in baseline pain symptoms, severity of baseline symptoms, and early improvement of abdominal pain. These findings have significant implications for clinical trial design.

Understanding statistical hypothesis tests and power

edical researchers often attempt to understand whether a risk factor is involved in the aetiology Mof disease or whether an intervention reduces disease; this has been the subject of another article in this series. We typically do this by proposing scientific hypotheses fromwhich testable statistical hypotheses can be developed. For example, our scientific hypothesis could be that people with irritable bowel syndrome (IBS) have higher risk of depression compared with those who do not have IBS. A small studymight show that one in ten in the control group have depression, comparedwith two in ten in the IBS group. This might reflect a real difference in the rate of depression between IBS and non-IBS populations, or the difference of one person between groups might simply be the play of chance. An empirical approach to answering this question might be to repeat the studymultiple times,with larger numbers, and to look at the consistency of the results. Unfortunately, this is an expensive and time-consuming solution.

An integrated approach examining the relationship of coping and psychological factors with gastrointestinal symptom burden

A systematic review of randomized controlled trials studying the preventive effects of physical exercise, manual and behavioural treatments in acute low back pain and neck painIntroduction: The global financial crisis has left governments struggling to reduce their budget deficits. Loans and taxes are two important financial instruments for governments to close their budget gaps. According to models of temporal discounting and expected utility individuals should experience loans as a greater loss than taxes, depleting psychological resources and reducing individuals’ capacity to cope with stressors. The present research examined patterns of cardiovascular (CV) reactivity associated with exposure to loans or taxes. Methods: We randomised 73 students to one of three groups: loans, taxes, control (baseline). Participants in the experimental groups imagined finishing university with debts and having to repay the sums outstanding as a proportion of their salaried income over the next 30 years either via a loan repayment, or via taxes. Participants in the control group imagined finishing university, and then working in salaried employment over the next 30 years. All participants then performed a variant of the Trier Social Stress Test (TSST), whilst CV responses were monitored [BP (blood pressure), ECG (electrocardiogram), ICG (impedance cardiogram)]. Results: Compared to the control group, participants in the loan group exhibited maladaptive CV responses during the stress task (higher BP and higher total peripheral resistance [TPR]). Conversely, participants in the taxes group exhibited more adaptive CV responses and did not differ from the control group. Conclusions: Economic considerations have dominated debates surrounding macro-financial performance. The present research highlights the need to consider the psychological costs and benefits of tax-based and loan-based financial instruments.

Somatization is key in the overlap between functional gastrointestinal disorders and other functional somatic syndromes

A systematic review of randomized controlled trials studying the preventive effects of physical exercise, manual and behavioural treatments in acute low back pain and neck painIntroduction: The global financial crisis has left governments struggling to reduce their budget deficits. Loans and taxes are two important financial instruments for governments to close their budget gaps. According to models of temporal discounting and expected utility individuals should experience loans as a greater loss than taxes, depleting psychological resources and reducing individuals’ capacity to cope with stressors. The present research examined patterns of cardiovascular (CV) reactivity associated with exposure to loans or taxes. Methods: We randomised 73 students to one of three groups: loans, taxes, control (baseline). Participants in the experimental groups imagined finishing university with debts and having to repay the sums outstanding as a proportion of their salaried income over the next 30 years either via a loan repayment, or via taxes. Participants in the control group imagined finishing university, and then working in salaried employment over the next 30 years. All participants then performed a variant of the Trier Social Stress Test (TSST), whilst CV responses were monitored [BP (blood pressure), ECG (electrocardiogram), ICG (impedance cardiogram)]. Results: Compared to the control group, participants in the loan group exhibited maladaptive CV responses during the stress task (higher BP and higher total peripheral resistance [TPR]). Conversely, participants in the taxes group exhibited more adaptive CV responses and did not differ from the control group. Conclusions: Economic considerations have dominated debates surrounding macro-financial performance. The present research highlights the need to consider the psychological costs and benefits of tax-based and loan-based financial instruments.

Explaining the placebo response with symptom burden and illness expectancy

A systematic review of randomized controlled trials studying the preventive effects of physical exercise, manual and behavioural treatments in acute low back pain and neck painIntroduction: The global financial crisis has left governments struggling to reduce their budget deficits. Loans and taxes are two important financial instruments for governments to close their budget gaps. According to models of temporal discounting and expected utility individuals should experience loans as a greater loss than taxes, depleting psychological resources and reducing individuals’ capacity to cope with stressors. The present research examined patterns of cardiovascular (CV) reactivity associated with exposure to loans or taxes. Methods: We randomised 73 students to one of three groups: loans, taxes, control (baseline). Participants in the experimental groups imagined finishing university with debts and having to repay the sums outstanding as a proportion of their salaried income over the next 30 years either via a loan repayment, or via taxes. Participants in the control group imagined finishing university, and then working in salaried employment over the next 30 years. All participants then performed a variant of the Trier Social Stress Test (TSST), whilst CV responses were monitored [BP (blood pressure), ECG (electrocardiogram), ICG (impedance cardiogram)]. Results: Compared to the control group, participants in the loan group exhibited maladaptive CV responses during the stress task (higher BP and higher total peripheral resistance [TPR]). Conversely, participants in the taxes group exhibited more adaptive CV responses and did not differ from the control group. Conclusions: Economic considerations have dominated debates surrounding macro-financial performance. The present research highlights the need to consider the psychological costs and benefits of tax-based and loan-based financial instruments.