What Drives Taxi Drivers? A Field Experiment on Fraud in a Market for Credence Goods

Credence goods are characterized by informational asymmetries between sellers and consumers that invite fraudulent behavior by sellers. This paper presents the results of a natural field experiment on taxi rides in Athens, Greece, set up to measure different types of fraud and to examine the influence of passengers’ presumed information and income on the extent of fraud. Results reveal that taxi drivers cheat passengers in systematic ways: Passengers with inferior information about optimal routes are taken on longer detours while asymmetric information on the local tariff system leads to manipulated bills. Higher income seems to lead to more fraud.credence goods, expert services, natural field experiment, taxi rides, fraud, asymmetric information

What drives taxi drivers? A field experiment on fraud in a market for credence goods

Credence goods are characterized by informational asymmetries between sellers and consumers that invite fraudulent behavior by sellers. This paper presents the results of a natural field experiment on taxi rides in Athens, Greece, set up to measure different types of fraud and to examine the influence of passengers’ presumed information and income on the extent of fraud. Results reveal that taxi drivers cheat passengers in systematic ways: Passengers with inferior information about optimal routes are taken on longer detours while asymmetric information on the local tariff system leads to manipulated bills. Higher income seems to lead to more fraud.Credence goods, expert services, natural field experiment, taxi rides, fraud, asymmetric information

What Drives Taxi Drivers? A Field Experiment on Fraud in a Market for Credence Goods

Credence goods are characterized by informational asymmetries between sellers and consumers that invite fraudulent behavior by sellers. This paper presents the results of a natural field experiment on taxi rides in Athens, Greece, set up to measure different types of fraud and to examine the influence of passengers' presumed information and income on the extent of fraud. Results reveal that taxi drivers cheat passengers in systematic ways: Passengers with inferior information about optimal routes are taken on longer detours while asymmetric information on the local tariff system leads to manipulated bills. Higher income seems to lead to more fraud.fraud, taxi rides, natural field experiment, expert services, credence goods, asymmetric information

The hidden costs of tax evasion. Collaborative tax evasion in markets for expert services

AbstractWe experimentally examine the impact of tax evasion attempts on the performance of credence goods markets, where contractual incompleteness results from asymmetric information on the welfare maximizing quality of the goods. Our results suggest that tax evasion attempts – independently of whether they are successful or not – lead to efficiency losses in the form of too low quality and less frequent trade. Thus, shadow economies may reduce welfare not only by inducing agents to incur costs to hide or to uncover taxable transactions, by imposing risk on uncertainty-averse tax evaders and by distorting competition, but also by creating an additional efficiency loss in the underlying market by forfeiting possible gains from trade and by inducing insufficient quality provision. We call these the hidden costs of tax evasion

Femoral anteversion change is associated with ischiofemoral impingement after total hip arthroplasty: a retrospective CT evaluation

OBJECTIVES We evaluated the relationship between femoral anteversion (FA), FA change, and ischiofemoral impingement (IFI) and the relationship between FA, femoral offset (FO), and greater trochanteric pain syndrome (GTPS) after total hip arthroplasty (THA). MATERIALS AND METHODS In this retrospective study, two readers assessed FA and FO on CT images of 197 patients following primary THA with an anterior surgical approach between 2014 and 2021. FA change was calculated relative to preoperative CT, while FO change was calculated relative to preoperative radiographs and classified as decreased (≥-5 mm), increased (≥ + 5 mm), or restored (± 5 mm). Clinical and imaging data were analyzed for IFI and GTPS after surgery. Group differences were evaluated using Student's t-test, chi-square analysis, and receiver operating characteristic (ROC) analysis. RESULTS The change in FA was 3.6 ± 3.3° to a postoperative FA of 22.5 ± 6.8°, while FO increased by 1.7 ± 3.5 mm to a postoperative FO of 42.9 ± 7.1 mm. FA and FA change were higher in patients with IFI (p ≤ 0.006), while no significant difference was observed for patients with and without GTPS (p ≥ 0.122). IFI was more common in females (p = 0.023). In the ROC analysis, an AUC of 0.859 was observed for FA change to predict IFI, whereas the AUC value was 0.726 for FA alone. No significant difference was found for FO change in patients with and without IFI or GTPS (p ≥ 0.187). CONCLUSION Postoperative FA, FA change, and female sex were associated with IFI after anterior-approached THA. The change in FA was a better predictor of IFI than absolute postoperative FA alone. CLINICAL RELEVANCE STATEMENT The findings of this study suggest that preservation of the preoperative femoral anteversion may reduce postoperative ischiofemoral impingement in patients undergoing total hip arthroplasty. KEY POINTS • Higher postoperative femoral anteversion and anteversion change were associated with ischiofemoral impingement. • Femoral anteversion change was a better predictor of impingement than absolute postoperative anteversion. • No significant association was found between femoral offset and postoperative hip pain

Policy or person?:What voters want from their representatives on Twitter

Social media have the potential to transform democracies as they allow for direct contact between representatives and represented. Politicians can use social media to show their policy positions but they can also give insight into their private lives. Based on survey experiments in Germany and Switzerland we show that social media messages about politicians’ private lives rather deter voters. Instead, we find that voters prefer candidates that communicate policy positions. The effect of a policy-oriented communication style on Twitter can even lead to appreciating a politician from a different party in Switzerland, which has an electoral system that gives a strong incentive to cultivate a personal vote

Quantifying cup overhang after total hip arthroplasty: standardized measurement using reformatted computed tomography and association of overhang distance with iliopsoas impingement

OBJECTIVES Currently, there is no standardized measurement method for evaluating cup overhang (CO) in patients undergoing total hip arthroplasty (THA). We propose a novel, standardized method of measuring overhang distance in patients following primary total hip arthroplasty (THA) on computed tomography (CT) images after multiplanar reformation and compare it to a previously proposed measurement method on sagittal CT images. MATERIALS AND METHODS This retrospective study included patients who underwent primary THA with an anterior approach. Patients with cup overhang (CO) and iliopsoas impingement (IPI) were identified by clinical and imaging data. Uncorrected overhang distance (OD$_{u}$) was evaluated on orthogonal sagittal CT images while corrected overhang distance (OD$_{c}$) was evaluated on reformatted sagittal CT images corrected for pelvic rotation and aligned with the plane of the cup face. RESULTS Out of 220 patients with THA, 23 patients (10.4%) with CO and 16 patients (7.3%) with IPI were identified. CO was significantly associated to IPI (p < 0.001). The inter- and intrareader agreement was almost perfect for OD$_{c}$ (κ = 0.822, κ = 0.850), whereas it was fair and moderate for OD$_{u}$ (κ = 0.391, κ = 0.455), respectively. The discriminative ability of OD$_{c}$ was excellent (area under the curve (AUC) = 0.909 (95% confidence interval (CI) 0.784-1.000)) in the receiver operating characteristic analysis. Conversely, AUC for OD$_{u}$ was poor, measuring 0.677 (95% CI 0.433-0.921). CONCLUSION We implemented a novel measurement method for CT images reformatted at the plane of the cup face to assess overhang distance in patients with CO following THA. CLINICAL RELEVANCE STATEMENT While further validation is necessary, the proposed method is characterized by its high reproducibility and might be used to predict the occurrence of iliopsoas impingement in patients with cup overhang following total hip arthroplasty. KEY POINTS • A novel, standardized method of measuring cup overhang distance in patients following primary total hip arthroplasty on CT images is proposed. • Cup overhang was associated to iliopsoas impingement. The proposed method was reproducible and showed excellent prediction of iliopsoas impingement in patients with cup overhang. • This method can be implemented in clinical practice when assessing CT images of patients with cup overhang for iliopsoas impingement

How accurate is MRI for diagnosing tarsal coalitions? A retrospective diagnostic accuracy study

OBJECTIVES This study aimed to evaluate the diagnostic accuracy, inter-reader agreement, and associated pathologies on MR images of patients with confirmed TC. METHODS AND MATERIALS In this retrospective study, 168 ankle MRI exams were included, consisting of 56 patients with clinically or surgically confirmed TC and 112 controls without TC, matched for age and sex. Images were analyzed independently by three radiologists blinded to clinical information. The evaluation criteria included the presence, type, and location of TC, as well as associated pathologies. After calculating diagnostic accuracy and the odds ratio of demographic data and anatomic coalition type for associated pathologies, inter-reader agreement was assessed using kappa statistics. RESULTS The majority of TCs were non-osseous (91.1%) and located at the calcaneonavicular (33.9%) or talocalcaneal joint (66.1%). Associated pathologies included adjacent and distant bone marrow edema (57.1% and 25.0%), osteochondral defect of the talar dome (OCD, 19.6%), and joint effusion (10.7%) and accessory anterolateral talar facet (17.9%). Talar OCD was associated with increased patient age (p = 0.03). MRI exhibited a cumulative sensitivity and specificity of 95.8% and 94.3% with almost perfect inter-reader agreement (κ = 0.895). CONCLUSION MRI is a reliable method for detecting tarsal coalition and identifying commonly associated pathologies. Therefore, we recommend the routine use of MRI in the diagnostic workup of patients with foot pain and suspected tarsal coalition. CLINICAL RELEVANCE STATEMENT MRI is an accurate and reliable modality for diagnosing tarsal coalitions and detecting associated pathologies, while improving patient safety compared to computed tomography by avoiding radiation exposure. KEY POINTS • Despite the technological progress in magnetic resonance imaging (MRI), computed tomography (CT) is still regarded as the gold standard for diagnosing tarsal coalition (TC). • MRI had a cumulative sensitivity of 95.8% and specificity of 94.3% for detecting tarsal coalition with an almost perfect inter-reader agreement. • MRI demonstrates high accuracy and reliability in diagnosing tarsal coalitions and is useful for identifying associated pathologies, while also improving patient safety by avoiding radiation exposure

7 T MRI of the Cervical Neuroforamen: Assessment of Nerve Root Compression and Dorsal Root Ganglia in Patients With Radiculopathy

OBJECTIVES: The aim of this study was to assess the diagnostic value of 3-dimensional dual-echo steady-state (DESS) magnetic resonance imaging (MRI) of the cervical spine at 7 T compared with 3 T in patients with cervical radiculopathy. MATERIALS AND METHODS: Patients diagnosed with cervical radiculopathy were prospectively recruited between March 2020 and January 2023 before undergoing surgical decompression and received 3-dimensional DESS imaging at 3 T and 7 T MRI. Cervical nerve root compression and the dimensions of the dorsal root ganglia were assessed by 2 radiologists independently. Signal intensity, visibility of nerve anatomy, diagnostic confidence, and image artifacts were evaluated with Likert scales. The degree of neuroforaminal stenosis was assessed on standard clinical 3 T scans. Statistics included the analysis of the diagnostic accuracy and interreader reliability. The Wilcoxon signed rank test was used to assess differences between the groups. RESULTS: Forty-eight patients (mean age, 57 ± 12 years; 22 women) were included in the study with the highest prevalence of severe neuroforaminal stenosis observed at C6 (n = 68) followed by C7 (n = 43). Direct evaluation of nerve root compression showed significantly higher diagnostic confidence and visibility of cervical nerve rootlets, roots, and dorsal root ganglia on 7 T DESS than on 3 T DESS (diagnostic confidence: P = 0.01, visibility: P < 0.01). Assessment of nerve root compression using 7 T DESS allowed more sensitive grading than standard clinical MRI (P < 0.01) and improved the performance in predicting sensory or motor dysfunction (area under the curve combined: 0.87). CONCLUSIONS: 7 T DESS imaging allows direct assessment of cervical nerve root compression in patients with radiculopathy, with a better prediction of sensory or motor dysfunction than standard clinical MRI. Diagnostic confidence and image quality of 7 T DESS were superior to 3 T DESS