Pre-post effect sizes should be avoided in meta-analyses.

Aims The standardised mean difference (SMD) is one of the most used effect sizes to indicate the effects of treatments. It indicates the difference between a treatment and comparison group after treatment has ended, in terms of standard deviations. Some meta-analyses, including several highly cited and influential ones, use the pre-post SMD, indicating the difference between baseline and post-test within one (treatment group). METHODS: In this paper, we argue that these pre-post SMDs should be avoided in meta-analyses and we describe the arguments why pre-post SMDs can result in biased outcomes. RESULTS: One important reason why pre-post SMDs should be avoided is that the scores on baseline and post-test are not independent of each other. The value for the correlation should be used in the calculation of the SMD, while this value is typically not known. We used data from an 'individual patient data' meta-analysis of trials comparing cognitive behaviour therapy and anti-depressive medication, to show that this problem can lead to considerable errors in the estimation of the SMDs. Another even more important reason why pre-post SMDs should be avoided in meta-analyses is that they are influenced by natural processes and characteristics of the patients and settings, and these cannot be discerned from the effects of the intervention. Between-group SMDs are much better because they control for such variables and these variables only affect the between group SMD when they are related to the effects of the intervention. CONCLUSIONS: We conclude that pre-post SMDs should be avoided in meta-analyses as using them probably results in biased outcomes.

The effects of cognitive and behavioural therapies for anxiety disorders on depression: a meta-analysis.

BACKGROUND: The effects of cognitive behavioural therapy of anxiety disorders on depression has been examined in previous meta-analyses, suggesting that these treatments have considerable effects on depression. In the current meta-analysis we examined whether the effects of treatments of anxiety disorders on depression differ across generalized anxiety disorder (GAD), social anxiety disorder (SAD) and panic disorder (PD). We also compared the effects of these treatments with the effects of cognitive and behavioural therapies of major depression (MDD). METHOD: We searched PubMed, PsycINFO, EMBASE and the Cochrane database, and included 47 trials on anxiety disorders and 34 trials on MDD. RESULTS: Baseline depression severity was somewhat lower in anxiety disorders than in MDD, but still mild to moderate in most studies. Baseline severity differed across the three anxiety disorders. The effect sizes found for treatment of the anxiety disorders ranged from g = 0.47 for PD, g = 0.68 for GAD and g = 0.69 for SAD. Differences between these effect sizes and those found in the treatment of MDD (g = 0.81) were not significant in most analyses and we found few indications that the effects differed across anxiety disorders. We did find that within-group effect sizes resulted in significantly (p < 0.001) larger effect sizes for depression (g = 1.50) than anxiety disorders (g = 0.73-0.91). Risk of bias was considerable in the majority of studies. CONCLUSIONS: Patients participating in trials of cognitive behavioural therapy for anxiety disorders have high levels of depression. These treatments have considerable effects on depression, and these effects are comparable to those of treatment of primary MDD.

Mechanistic studies of pyridinium electrochemistry: alternative chemical pathways in the presence of CO2.

Protonated heterocyclic amines, such as pyridinium, have been utilized as catalysts in the electrocatalytic reduction of carbon dioxide. While these represent a new and exciting class of electrocatalysts, the details of the mechanism and faradaic processes occurring in solution are unclear. We report a series of cyclic voltammetry experiments involving Pt, Ag, Au, and Cu electrodes, under both aqueous and nonaqueous conditions, directed towards gaining an improved mechanistic understanding of pyridinium electrochemistry. Surface-enhanced Raman (SER) spectroelectrochemistry was also performed on Cu film-over-nanosphere electrodes in order to identify adsorbed species. It was found that the reduction potential of pyridinium (-0.58 V vs. SCE) and its electrochemical reversibility are unique features of platinum electrodes. In contrast, the reduction potentials on Ag, Au, and Cu electrodes are ∼400 mV more negative than Pt in both the presence and the absence of CO2. SER spectroelectrochemistry of pyridinium solutions shows no evidence for a pyridinium radical or a pyridinium ion. Increased cathodic current in the presence of CO2 is only detected at scan rates less than 10 mV s(-1) in aqueous solutions. The addition of CO2 resulted in a shift in the potential for the hydrogen evolution reaction. Pyridinium electrochemistry was observed under nonaqueous conditions; however no increase in cathodic current was observed when CO2 was added to the solution. Based on this set of results it is concluded that the reduction potential of pyridinium is surface dependent, CO2 acts as a pseudo-reserve of H(+), and pyridinium and CO2 create an alternative mechanism for hydrogen evolution.

Experimental determination of the Cr-C(2)Cl(4) bond dissociation enthalpy in Cr(CO)(5)(C(2)Cl(4)): quantifying metal-olefin bonding interactions.

The bond dissociation enthalpy for the Cr-C(2)Cl(4) bond in gas-phase Cr(CO)(5)(C(2)Cl(4)) has been determined to be 12.8 +/- 1.6 kcal/mol using transient infrared spectroscopy. The results of a density functional theory-based energy decomposition analysis are used to quantify the metal-olefin bonding interactions in terms of the bonding description provided by the Dewar-Chatt-Duncanson model (sigma donation and back-bonding). The bond energy decomposition analysis reveals that metal-olefin bond strengths can be strongly influenced by the Pauli repulsion energy and by the energy necessary to deform the olefin and the metal-centered moiety from their equilibrium geometries to their geometry in the final complex. Further, a comparison between the metal-olefin bond strengths and the magnitude of the electronic interactions demonstrates that the energy associated with these deformations is the determining factor in the trends in bond enthalpies in the series of complexes Cr(CO)(5)(C(2)X(4)) (X = H, F, Cl). Though deformation of the Cr(CO)(5) moiety contributes to the overall deformation energy, the major contribution involves deformation of the olefin. This occurs as a consequence of rehybridization of the olefin as a result of metal-olefin back-bonding. The results are discussed in terms of the Dewar-Chatt-Duncanson model, which provides the accepted qualitative description of bonding in organometallic olefin complexes.

Isokinetic trunk strength and lifting strength measures. Differences and similarities between low-back-injured and noninjured workers.

Fifty-eight back pain patients and 21 entry-level Postal Service workers without low-back pain were evaluated using a variety of lumbar function measures. Isolated trunk strength and full lifting strength were gauged with isokinetic and isometric methods. Lumbar range-of-motion was computed using toe-touch and goniometers. Conventional clinical techniques such as toe touch and straight leg raise were effective in distinguishing back-injured from normal subjects. Isometric and isokinetic peak force and torque tests failed to show significant differences between low-back pain and job applicant groups. When compared with published norms, our job applicant group was significantly deconditioned. Our data suggest that asymptomatic, deconditioned subjects could be mistaken for back-impaired patients or symptom magnifiers.

The lateral bending sign.

In lumbar disc herniations, musculoskeletal findings usually predominate at the outset. There is often an acute list or impaired lateral mobility to one side or the other. This finding represents a protective mechanism to splint the affected disc space in the position where the disc prolapse exerts the least possible pressure on the affected nerve root. An attempt was therefore made to determine whether the relationship of the disc herniation to the nerve root could be delineated by having the patient bend maximally to each side. Three hundred patients who would normally be candidates for routine (static) x-ray study of the lumbar spine had lateral bending (dynamic) films instead. These were then correlated with myelograms and/or surgery, when performed. Lateral bending roentgenograms can often pinpoint the level of lumbar disc herniation.