Field experiments in labor economics

In this thesis I show with three studies how field experiments can enhance our understanding of labor markets. Economists traditionally assume that individuals exclusively respond to monetary incentives. As a consequence, if workers have no prospect of future employment at the firm and pay is not contingent on their performance, a wage change should not affect effort. Some economists, however, have recognized that this narrow view of human motivation may severely limit our progress in understanding incentives. In Chapters 2 and 3, I investigate the role of psychological motives like the desire to reciprocate in the context of a real‐life work environment. The first experiment explores the impact of a wage increase on work performance when there is no economic reason for workers to change their effort. I find that workers reciprocate a generous wage with higher performance, particularly those workers who care about fairness and felt underpaid prior to the wage increase. The second experiment investigates the effects of a wage cut on performance when either all workers in a team or only some of them suffer the cut. I show that a general pay cut reduces performance, while a wage cut for only some of the workers reduces their performance more than twice as much. This finding demonstrates the powerful force of social comparison and the need to build the social nature of humans into economic theory. In Chapter 4, I examine the joint effects of monetary incentives and social interaction on work performance. Many jobs offer wage schemes that create positive or negative externalities on coworkers. Whether or not workers have the possibility to interact socially at work may distort the intended incentives of these schemes. I find that under relative incentives, when own effort imposes a negative externality on the coworker’s income, social interaction works against monetary incentives and leads to low performance due to collusion. However, the more workers differ in skills the less able they are to sustain collusive agreements. In der vorliegenden Dissertation zeige ich anhand von drei Studien wie Feldexperimente unser Verständnis von Arbeitsmärkten verbessern können. Ökonomen gehen traditionell davon aus, dass Individuen ausschliesslich auf materielle Anreize reagieren. Wenn also Arbeitskräfte keine Aussicht auf eine langfristige Anstellung haben und deren Lohn nicht von der Leistung abhängt, dann sollte eine Lohnveränderung keinen Einfluss auf die Arbeitsleistung haben. Manche Ökonomen haben jedoch erkannt, dass diese Sichtweise des menschlichen Verhaltens beschränkt ist und unseren Fortschritt im Verständnis von Anreizen bremsen kann. In den Kapiteln 2 und 3 untersuche ich die Bedeutung von psychologischen Motiven wie Fairness oder Reziprozität in echten Arbeitsumgebungen. Das erste Experiment untersucht den Einfluss einer Lohnerhöhung auf die Arbeitsleistung, wenn Arbeitskräfte keinen ökonomischen Grund haben, ihren Arbeitseinsatz zu ändern. Diese Studie zeigt, dass Arbeitskräfte einen grosszügigen Lohn mit höherer Arbeitsleistung erwidern. Dies gilt besonders für diejenigen, die Fairness als wichtig empfinden und sich vor der Lohnerhöhung unterbezahlt fühlten. Das zweite Experiment untersucht die Wirkung einer Lohnkürzung auf die Arbeitsleistung, wenn entweder das ganze Team oder nur einen Teil davon betroffen ist. Diese Studie zeigt auf, dass eine generelle Lohnkürzung die Arbeitsleistung senkt, wohingegen eine Lohnkürzung nur für einzelne Arbeitskräfte deren Leistung um mehr als das Doppelte reduziert. Diese Erkenntnis unterstreicht die Bedeutung von sozialen Motiven und die Notwendigkeit einer Veränderung des Menschenbilds in der Ökonomie. In Kapitel 4 erforsche ich den gemeinsamen Einfluss von materiellen Anreizen und sozialer Interaktion auf die Arbeitsleistung. Viele Firmen bieten Lohnsysteme an, bei welchen die eigene Leistung vor‐ oder nachteilhafte Nebeneffekte auf das Einkommen der Arbeitskollegen hat. Soziale Interaktion am Arbeitsplatz kann dabei die Anreize dieser Lohnsysteme verzerren. Diese Studie findet heraus, dass bei Entlohnung der Arbeitskräfte durch Turnieranreize, d.h. wenn die eigene Leistung sich nachteilhaft auf das Einkommen der Arbeitskollegen auswirkt, soziale Interaktion die Anreize ausser Kraft setzt und zu geheimen Absprachen führt. Wenn hingegen Arbeitskräfte sehr unterschiedliche Fähigkeiten besitzen, dann sind geheime Absprachen schwieriger aufrecht zu halten

Streaming Video using PDA and 3G Wireless Communications for Viewing Large Quantities of Diagnostic Images.

Streaming方式を使った、医療画像の転送方式を提案し、実演した。PDAを端末とし、無線LANを用いて、実際の医療画像（CT,MRI等）の転送の実演を行った。Infora

Development Of Radial Echo Planar Imaging with Central High-Resolution Area ( REPI with CHRA )

PurposeThe most challenging aspect of imaging dynamically changing objects by MRI is achieving the desired temporal resolution without sacrificing the required spacial resolution. The present authors have developed a new MRI sequence termed Radial Echo Planer Imaging with a Central High-Resolution Area (REPI with CHRA), in which high temporal resolution is balanced with high spatial resolution in the center of the field of view (FOV). \nMethodUsing a 1.5T Sigma Horizon LX MRI system (GE Medical Systems, Milwaukee, WI, U.S.A.) and EPIC (Environment for Programming in C), we developed the REPI with CHRA technique, in which radii of a sector area of k-space are scanned in one excitation, with the first radius being twice the width of the subsequent radii. The entire k-space is scanned in multiple excitations. After all radii other than the first in a sector area are zero-filled, the image is reconstructed by back projection. A MRI fluoroscopy of the heart and a contrast enhanced MR angiography (CEMRA) of the head were taken by applying REPI with CHRA continuously. \nResultsUsing 16-shot REPI with CHRA, with a FOV of 24 cm, we achieved a TR of 320 ms for the acquisition of a 128 ´ 128 image with a resolution of 1 mm in the center of the FOV and a resolution of 2 mm in the peripheral area. As REPI with CHRA is basically a radial sampling method, the image suffered less from the phase error artifacts characteristic of multi-shot EPI. Using 16-shot REPI with CHRA, we took images of the heart and CEMRA of the head both with a FOV of 24 cm, for 32 s. Using the view-sharing technique, we obtained images with a temporal resolution of 20 ms and a spatial resolution of 1 mm in the center area. The images exhibited fewer density discontinuities than by ordinary EPI. The motion artifact manifested as a star-like shadow, which offers greater clarity than the blurring characteristic of ordinary EPI. \nConclusionWe proved that REPI with CHRA can be used successfully to balance high temporal resolution with high spatial resolution, which is necessary for imaging dynamically changing objects. The images produced using the technique exhibit minimal density discontinuity, and less obtrusive motion artifacts. These characteristics render this technique suitable for imaging moving objects or for CEMRA

PDA with High-risolution Display and Mobile Wireless File Server System

We developed a new mobile system for radiologists using a PDA with a high resolution display and personal mobile server (PMS). Our system consists of PDSq with VGA display and the PMS. The PMS, which is 390 grams, with a high 20GB hard disk drive and wireless LAN access point built into device, supports acess via FTP file transfer protocol, CIFS, and NFS. The PMS can access from the wireless LAN correspondence PCs, PDAs, and client & server system at any time. Operating system of both PDAs and PMS is Linux.InforRa

Development and performance evaluation of cone beam CT using video-fluoroscopic system

We describe the development and performance evaluation of cone beam CT. This CT is based on video-fluoroscopic system and yields data that is amenable to three-dimensional (3D) image processing. An X-ray tube and a large area two-dimensional detector were mounted on a single frame and rotated around objects in 12 seconds. The large area detector consisted of a fluorescent plate and a charge coupled device (CCD) video camera. While the X-ray tube was rotated around the object, a pulsed X-ray was generated (30 pulses per second) and 360 projected images were collected in a 12-second scan. A 256x256x256 matrix image was reconstructed using a high-speed parallel processor with reconstruction time of 6 minutes. Image characteristics such as spatial resolution, image noise and distortion were evaluated by phantoms. The results showed isotropic spatial resolution and no distortion of images though they showed larger image noise than conventional CT

MR Diffusion-weighted imaging(DWI) of Malignant Melanoma in Head and Neck after Accelerated Carbon-Ion Radiotherapy

PURPOSE: To report change of diffusion weighted imaging(DWI) of malignant melanoma in head and neck after carbon-ion radiotherapy. MATERIAL and METHOD: Eighteen patients having malignant melanoma in head and neck regions undertook carbon-ion radiotherapy at the National Institute of Radiological Sciences, Chiba, Japan. We examined using DWIBS (diffusion-weighted imaging with background body signal suppression) method before and after the treatment. ADC (apparent diffusion coefficient) value was measurable in nine of 18 cases (mean age:65yrs,age range:56-78,5 males and 4 females). We compared the ADC value before the treatment with the after one. Intera Achieva 1.5T Nova Dual system (Philips Medical) was used for the examination. The EPI-based diffusion-weighted imaging sequence with SPIR fat suppression was applied at the settings of two b-values, namely 0 and 1000 sec/mm^2, respectively. Results: Average ADC value for all clinical cases were 0.897x10^-3 (S.D.: 0.142x10^-3) at pre-treatment and 1.355x10^-3 (S.D.: 0.573x10^-3) at post-treatment. ADC values were increased in eight of 9 cases and decreased in one. There was a significant difference in ADC value between pre- and post-treatment (P<0.028).CONCLUSIONS: DWIBS examination for malignant melanoma in head and neck showed significant increases in ADC value after carbon-ion radiotherapy. The ADC value has the possibility of becoming a criteria when you judge the effect of the carbon-ion radiotherapy in malignant melanoma.ECR2007 19th European Congress of Radiolog

Mobile Wireless DICOM Server System and PDA with High-Resolution Display:Feasibility of Group Work for Radiologists 1

A novel mobile system has been developed for use by radiologists in managing Digital Imaging and Communications in Medicine (DICOM) image data. The system consists of a mobile DICOM server (MDS) and personal digital assistants (PDAs), including a Linux PDA with a video graphics array (VGA) display (307,200 pixels, 3.7 inches). The MDS weighs 410 g, has a 60-GB hard disk drive and a built-in wireless local area network (LAN) access point, and supports a DICOM server (Central Test Node). The Linux-based MDS can be accessed with personal computers (PCs) and PDAs by means of a wireless or wired LAN, and client-server communications can be established at any time. DICOM images can be displayed by using any PDA or PC by means of a Web browser. Simultaneous access to the MDS is possible for multiple authenticated users. With most PDAs, image compression is necessary for complete display of DICOM images; however, the VGA screen can display a 512 x 512-pixel DICOM image almost in its entirety. This wireless system allows efficient management of heavy loads of lossless DICOM image data and will be useful for collaborative work by radiologists in education, conferences, and research