Scale, scope, and spillovers: the determinants of research productivity in drug discovery

We examine the relationship between firm size and research productivity in the pharmaceutical industry. Using detailed internal firm data, we find that larger research efforts are more productive, not only because they enjoy economies of scale, but also because they realize economies of scope by sustaining diverse portfolios of research projects that capture internal and external knowledge spillovers. In pharmaceuticals, economies of scope in research are important in shaping the boundaries of the firm, and it may be worth tolerating the static efficiency loss attributable to the market power of large firms in exchange for their superior innovative performance.

MRC image processing programs

Digital image processing is an essential step in the determination of macromolecular structures by electron microscopy. Centrally important procedures are the averaging of many images of the subunit to improve the signal, the correction for various transfer functions, and the generation of a three-dimensional map from a set of two-dimensional projections. The detailed way in which these computational procedures are best carried out depends on the symmetry of the object and the type of specimen preparation. Over many years a large set of programs has been written by various members of the Laboratory of Molecular Biology for processing images of two-dimensional crystals and of particles with helical or icosahedral symmetry. The philosophy has been to write stand-alone programs and the whole system is given coherence by the adoption of standard formats for the storage and interchange of different kinds of data. This paper describes the current state of the programs.

Modelling conditional distributions in bivariate survival

Conditional distributions for bivariate survival can be obtained via a model for the joint distribution, or, as has sometimes been suggested, by modelling the conditioned variable directly, with the conditioning variable included as a covariate. A quantitative comparison of estimated covariate effects and predictive distributions under the two approaches is given. The results are illustrated in a novel frailty application.

Freeze trapping of reaction intermediates

Structural intermediates in a biological reaction may be monitored by rapid spectroscopic or somewhat slower structural techniques. Intermediates may evolve in real time (no trapping), be stabilized by chemical manipulation of the reactants, the macromolecule or the solvent (chemical trapping), or be stabilized by lowering the temperature (freeze trapping). The last is beginning to be coupled with X-ray diffraction, electron cryomicroscopy and solid-state NMR approaches to characterize the trapped intermediates. Care in conducting such experiments, together with an awareness of possible artefacts, is essential if reliable structural results are to be obtained.

Incidence of de-novo breast cancer in women chronically immunosuppressed after organ transplantation

In mice, retrovirus-associated breast cancers are promoted by immune mechanisms, and immunosuppression during the premalignant phase reduces the incidence of breast cancer and prolongs life. If some women likewise have immune promotion of breast cancer, the incidence of breast cancer in patients receiving therapeutic immunosuppression should be lower than that in a comparable cohort of non-immunosuppressed women. We examined the incidence of de-novo breast cancer arising in women receiving immunosuppressive therapy after kidney or heart transplantation, comparing the figures with published rates. In 25,914 immunosuppressed women followed for 1-11 years there were 86 cases of breast cancer compared with 113.8 expected (p = 0.009). Incidence was particularly low in the first transplant year with relative risk 0.49, rising to 0.84 in subsequent years. For all other major cancers the incidence was higher in the immunosuppressed women. If, as in mice, the reduced incidence of breast cancer is a direct effect of immunosuppression, these observations raise the possibility of therapeutic manipulation of specific immune mechanisms that promote tumour growth.

Assessment of satisfaction with computer training in a healthcare setting

The use of computers in healthcare settings has become increasingly common. However, issues of training and training assessment have received scant attention. The main aim of the current study was to assess the use of consumer satisfaction data for evaluation and development of computer training packages in healthcare settings. One hundred and thirty-six randomly selected people completed a brief satisfaction questionnaire at the completion of computer training. The effects of different teachers, course duration, course complexity, and changes in satisfaction over time were examined. The use of a customer satisfaction approach to training evaluation is discussed.

A review of current toothbrush bristle endo-rounding studies

Rounded toothbrush bristle tips are desirable because they are less likely to abrade hard and soft tissue and restorative materials than sharp-pointed bristles. Studies evaluating different types of toothbrushes have compared the degree of the end-roundness of different brands of toothbrushes, but have yielded conflicting results. Nine studies and three methods of evaluating end-rounding are reviewed in this article. Within the limits of the review, it appears that visual inspection of a bristle tip by scanning electron microscopy or a stereomicroscope at a 45-degree angle is the technique of choice for evaluating end-roundness. Of the 9 studies reviewed, 3 studies that used the 45-degree microscopic techniques provide the most useful information of toothbrush bristle end-roundness to date. Of the brushes compared in these three studies, Crest Complete and Improved Crest Complete toothbrushes were shown to have the highest degree of end-roundness. Future research should include longitudinal studies to clarify the relationship of the degree of end-rounding of toothbrush bristles and soft-and hard-tissue abrasion.

The effect of induced reflections on human arterial waveforms

1. External compression of the human brachial artery results in waveform reflection. 2. Resonant waves are found superimposed on the original blood pressure signal. 3. The mechanism may be likened to the operation of an organ pipe with reflections at both ends of an arterial segment. 4. This has implications for measurements in arteries where external pressure is applied.

The potential and limitations of neutrons, electrons and X-rays for atomic resolution microscopy of unstained biological molecules

Radiation damage is the main problem which prevents the determination of the structure of a single biological macromolecule at atomic resolution using any kind of microscopy. This is true whether neutrons, electrons or X-rays are used as the illumination. For neutrons, the cross-section for nuclear capture and the associated energy deposition and radiation damage could be reduced by using samples that are fully deuterated and 15N-labelled and by using fast neutrons, but single molecule biological microscopy is still not feasible. For naturally occurring biological material, electrons at present provide the most information for a given amount of radiation damage. Using phase contrast electron microscopy on biological molecules and macromolecular assemblies of approximately 10(5) molecular weight and above, there is in theory enough information present in the image to allow determination of the position and orientation of individual particles: the application of averaging methods can then be used to provide an atomic resolution structure. The images of approximately 10,000 particles are required. Below 10(5) molecular weight, some kind of crystal or other geometrically ordered aggregate is necessary to provide a sufficiently high combined molecular weight to allow for the alignment. In practice, the present quality of the best images still falls short of that attainable in theory and this means that a greater number of particles must be averaged and that the molecular weight limitation is somewhat larger than the predicted limit. For X-rays, the amount of damage per useful elastic scattering event is several hundred times greater than for electrons at all wavelengths and energies and therefore the requirements on specimen size and number of particles are correspondingly larger. Because of the lack of sufficiently bright neutron sources in the foreseeable future, electron microscopy in practice provides the greatest potential for immediate progress.

Three-dimensional structure of halorhodopsin at 7 A resolution

Two-dimensional crystalline patches containing the light-driven chloride pump, halorhodopsin, appear to form spontaneously in the cell membrane of an overproducing strain of Halobacterium. The three-dimensional structure (space group p42(1)2, a = 102 A) has been analysed by electron cryo-microscopy of tilted specimens. The map shows that halorhodopsin (HR) has an arrangement of seven transmembrane helices similar to that found in the related proton pump bacteriohodopsin (BR). The orientation of the polypeptide framework of HR in the membrane is rotated by 3 degrees relative to BR about an axis in the plane and the intramolecular space between the helices BC FG, which line the cytoplasmic half channel, appears slightly larger in HR than in BR, as would be expected for a chloride channel. The crystals of HR were too small for electron diffraction analysis of tilted specimens, so both the amplitudes and the phases of the Fourier components were obtained from images. This required anisotropic scaling of the image amplitudes in addition to correction for the defocus phase contrast transfer function. The procedure of rescaling the data (in this case roughly equivalent to sharpening with a temperature factor of-490) to compensate for a variety of image and crystal defects may also prove useful in the analysis of other structures for which no prior knowledge of a homologous structure exists and for which only small crystals can be obtained.

Problems and prediction in survival-data analysis

Twenty-one years after its appearance, Cox's 1972 paper on 'Regression models and life tables' continues to be one of the most frequently cited publications in the scientific and medical literature. The proportional-hazards model and partial-likelihood technique have been applied to thousands of data sets, not always appropriately, and have motivated hundreds of theoretical studies, not always relevant. Recent developments are reviewed and continuing problems discussed, especially with respect to predictive inference. The accuracy of model-based predictions, and how they compare with consultants' judgements are investigated by means of an example.

Sequelae of Haemophilus influenzae type b meningitis in aboriginal and non-aboriginal children under 5 years of age

Between 1984 and 1990, 257 cases of Haemophilus influenzae type b (Hib) meningitis occurred in children under five years of age in Western Australia. We obtained information on possible sequelae in 131 cases (all non-Aboriginal) by medical record review and parental interview, and in a further 116 cases (60 non-Aboriginal, 56 Aboriginal) by medical record review only; no follow-up information was available for ten children (nine non-Aboriginal, 1 Aboriginal). The incidence of Hib meningitis in children under five years of age was 26.3 per 100,000 for non-Aboriginal and 152.2 per 100,000 for Aboriginal children. The case fatality rate was 3.5% for non-Aboriginal children and 14.0% for Aboriginal children. Sequelae were recorded for 17.1% of non-Aboriginal and 22.4% of Aboriginal children who survived Hib meningitis. Surviving Aboriginal children experienced severe sequelae following Hib meningitis almost three times more frequently than surviving non-Aboriginal children (10.5% vs 3.6%), although mild and moderate sequelae were not more common in Aboriginal children. The information on incidence and severity of sequelae in this study was obtained by chart review and parental interview, and hence may be subject to error or bias, particularly for mild and moderate disabilities. Outcomes like death and severe sequelae, such as cerebral palsy and profound intellectual and physical disability, are less subject to bias. Of Aboriginal children who contracted Hib meningitis in Western Australia over the study period, 22.8% either died or had severe sequelae, while only 7.0% of non-Aboriginal children experienced these severe outcomes.

Treatment of oral cancers using iridium-192 interstitial irradiation

OBJECTIVE

To assess retrospectively the outcome and morbidity of Iridium-192 brachytherapy in the treatment of oral cancers.

DESIGN

Retrospective audit of cases treated between 1981 and 1991.

SETTING

Newcastle upon Tyne, England.

SUBJECTS

73 patients with oral cancer treated with Iridium-192.

MAIN OUTCOME MEASURES

Local control, crude and cause specific survival, and local morbidity.

RESULTS

Seventy four cases of squamous cell carcinoma of the oral cavity were treated using interstitial Iridium-192. The disease specific 5-year survival rates were 69% for T1, 67% for T2, and 0% for T3 tumours. Mortality from recurrent cancer was 20%, and from intercurrent disease was 28%. The incidence of major radiation induced morbidity was 11%, and the local control rate was 81% for T1, 69% for T2, and 50% for T3 tumours.

CONCLUSION

Interstitial radiotherapy remains a viable and valuable mode of treatment for a small proportion of patients presenting with early (T1 and T2) oral cancers.

Analysis of electron microscope images and electron diffraction patterns of thin crystals of phi 29 connectors in ice

Images and diffraction patterns of frozen-hydrated thin crystals of phi 29 connectors were recorded using low dose microscopy and diffraction. The resolution obtained in two cases was 7 and 4 A, thus showing the suitability of this specimen for high-resolution studies. Seven of the best images and three of the best electron diffraction patterns were analysed semiquantitatively. The best image showed the presence of two connectors per unit cell (165 A x 165 A), each having an internal 4-fold axis and being related to one-another by 2-fold and 2-fold screw axes in the space group p42(1)2. Internal phase comparison within the best image showed good phase residuals for p42(1)2 and all its sub-groups. The other images were consistent with this interpretation taking into consideration the possible crystal tilt and specimen drift. We conclude that the most likely crystal space group is p42(1)2. Electron diffraction patterns were consistent with this assignment, but none of the patterns showed the precise 422 symmetry expected, almost certainly because the crystals were slightly tilted (2 to 5 degrees).

Incidence of non-Hodgkin lymphoma in kidney and heart transplant recipients

Organ transplant recipients receive immunosuppressive drugs to prevent graft rejection. This treatment has been associated with higher rates of non-Hodgkin lymphoma (NHL) than in the general population. We assessed the incidence of NHL in a multicentre study of 45,141 kidney transplant patients and 7634 heart transplant recipients. The NHL rate was especially high during the first post-transplant year among both kidney transplant recipients (101 cases vs 2.7 expected in general population; 224 per 10(5)) and heart transplant recipients (93 vs 0.6 expected; 1218 per 10(5)). The incidence was lower in subsequent years (43 and 371 per 10(5) in kidney and heart transplant recipients). During the first year the NHL incidence was higher in North America than in Europe (relative risk 2.12 [95% CI 1.55-2.89]). There were also significant increases in risk for patients who received rejection prophylaxis with antilymphocyte antibodies (1.80 [1.31-2.46]) and in those who received both cyclosporin and azathioprine rather than another immunosuppressive combination (1.47 [1.03-2.08]). This study quantified the risk of NHL after kidney or heart transplantation. It suggests that the risk of NHL is related to the aggressiveness of the immunosuppressive regimen.