Persistent Deviation Research Articles

Fundamentals to Diagnosing Polycystic Ovary Syndrome in Adolescents: A Critical Literature Review

Background: Because of this prevalence and frequent association with various comorbidites, the diagnosis of polycystic ovary syndrome (PCOS) must be performed as early as possible. Despite conflicting findings, many studies have been published on adolescents with a diagnosis of polycystic ovary syndrome. Methods: The Google Scholar and PubMed data bases were searched for publications in the English language reporting on PCOS diagnosis in adolescents. Results: A comprehensive analysis of data regarding the overlay of physiological ripening of menstrual cycle characteristics, androgen levels, and ovary aspects during puberty with the established criteria to diagnose PCOS in adults revealed that are liable diagnosis of PCOS in adolescence is possibleas soon as 2-3 years postmenarche. Persistant menstrual cycle intervals shorter than 21 days or longer than 45 days, total testosterone levels >1.9-2.0 nmol/l and ovary volume >10cm<sup>3 </sup>after 15-16 years of age can be used to diagnose PCOS. Conclusion: When combined, any persistent deviation of physiological parameters in adolescents as a criterion to diagnose PCOS in adults allows a certain diagnosis of PCOS in adolescents.

SUCCESSFUL DIFFERENT TREATMENT IN INTERMITTENT EXOTROPIA: CASE SERIES

Introduction : In intermittent exotropia, management's goals are to diminish deviation by improving fusion control.
 Case Illustration : Case 1: A 19-year-old woman has complained of squinting and blurred vision since the age of 3 years. The visual acuity of both eyes (OU) was 0.05, with a BCVA of 0.63. Hirschberg's test was exotropia 15o . The exotropia after the cover test (Figure 1A) improved without blinking. The prism cover test was 35 D in near and distance. Patient was diagnosed with exotropia, an intermittent basic type with good control, astigmatism, and myopia compositus OU. Three months after, with refraction correction and occlusion, the Hirschberg test revealed orthotropia (Figure 1B). Case 2: A 7-year-old boy has suffered of squinting and blurred vision from the age of 6 years. The visual acuity of both eyes was 0.63 with a BCVA of 1.0. Hirschberg's test was exotropia 30° (Figure 2A). The prism cover test was 50 D in near and distance. Exotropia intermittent basic type, poor control, and bilateral astigmatism were diagnosed in the patients. The patient had surgery for bilateral lateral rectus recession. Hirschberg test 1 day Postoperatively, orthotropia was present (Figure 2B).
 Discussion : In exodeviation, control mechanisms relate to therapy compliance and different deviation angles. Intermittent exotropia can be progressive due to loss of fusion control and cause persistent deviation.
 Conclusion : For patients with exotropia with intermittent good control, non-surgical management can give good results. Surgical management is considered for large angle deviations in patients with poor control.

Application of Dynamic Mode Decomposition to Characterize Temporal Evolution of Plantar Pressures from Walkway Sensor Data in Women with Cancer.

Pressure sensor-impregnated walkways transform a person's footfalls into spatiotemporal signals that may be sufficiently complex to inform emerging artificial intelligence (AI) applications in healthcare. Key consistencies within these plantar signals show potential to uniquely identify a person, and to distinguish groups with and without neuromotor pathology. Evidence shows that plantar pressure distributions are altered in aging and diabetic peripheral neuropathy, but less is known about pressure dynamics in chemotherapy-induced peripheral neuropathy (CIPN), a condition leading to falls in cancer survivors. Studying pressure dynamics longitudinally as people develop CIPN will require a composite model that can accurately characterize a survivor's gait consistencies before chemotherapy, even in the presence of normal step-to-step variation. In this paper, we present a state-of-the-art data-driven learning technique to identify consistencies in an individual's plantar pressure dynamics. We apply this technique to a database of steps taken by each of 16 women before they begin a new course of neurotoxic chemotherapy for breast or gynecologic cancer. After extracting gait features by decomposing spatiotemporal plantar pressure data into low-rank dynamic modes characterized by three features: frequency, a decay rate, and an initial condition, we employ a machine-learning model to identify consistencies in each survivor's walking pattern using the centroids for each feature. In this sample, our approach is at least 86% accurate for identifying the correct individual using their pressure dynamics, whether using the right or left foot, or data from trials walked at usual or fast speeds. In future work, we suggest that persistent deviation from a survivor's pre-chemotherapy step consistencies could be used to automate the identification of peripheral neuropathy and other chemotherapy side effects that impact mobility.

Concurrent Isolated Hypoglossal Nerve Palsy Induced by Jugular Vein Thrombosis, Cervical Plexus Masses, and Vestibular Schwannoma: A Complex Case Report Highlighting Anatomical Pathways and Clinical Challenges

Background: Hypoglossal nerve palsy is typically observed alongside other cranial nerve impairments, with isolated cases being infrequent and posing diagnostic complexities. Originating intracranially, the nerve traverses the skull and neck, governing tongue motility. Lesions are classified as supranuclear, nuclear, or infranuclear, engendering tongue deviation towards the affected side. Due to its proximity to crucial structures, hypoglossal nerve palsy often coincides with supplementary symptoms. Etiologies encompass skull base metastases, carotid artery pathologies, and trauma. This study explores less conventional triggers such as hypoglossal nerve palsy following thyroidectomy, jugular vein thrombosis, cervical plexus masses, and Vestibular Schwannoma. Case Description: A 38-year-old female presented to the Neurology outpatient clinic with leftward tongue deviation and left-sided neck and shoulder pain accompanied by stiffness that had begun several months prior. In addition to the tongue deviation, she reported minor dysphagia, blurry vision, and intermittent numbness on the left side of her scalp. MRI and duplex ultrasound verified the presence of left internal jugular vein (IJV) thrombosis. The patient was initially prescribed Eliquis and acetazolamide, with slight improvements in symptoms, though medication use ceased due to side effects. During a subsequent follow-up visit, persistent tongue deviation and worsening left shoulder pain prompted additional cervical imaging. A new cervical spine MRI revealed a 15x14 mm nodular dural enhancement with a paraspinal soft tissue mass at the C2 level. Concurrently, multiple cranial nerve palsies were detected during the physical examination. Unfortunately, the patient was subsequently diagnosed with breast cancer. To rule out brain metastases related to her breast cancer, an additional brain MRI was performed, revealing a newly formed 2.3x1.6x1.2 cm left cerebellopontine angle mass adjacent to the internal auditory canal (IAC), suggestive of a vestibular schwannoma but without evidence of metastatic disease. The patient's care involved a multidisciplinary team, including hematologist-oncologists, neurosurgeons, and neurologists. Conclusion: This case report highlights the less common causes of hypoglossal nerve palsy, such as jugular vein thrombosis, cervical plexus masses, and Vestibular Schwannoma. The persistence of the patient's palsy is attributed to the cumulative impact of these anatomical factors on the hypoglossal nerve. This underscores the diagnostic challenges posed by isolated hypoglossal nerve palsy and emphasizes the importance of comprehensive clinical evaluation and imaging for accurate diagnosis.

Endoscopic septoplasty versus conventional septoplasty for nasal septum deviation: a systematic review and meta-analysis of randomized clinical trials.

The authors searched five electronic databases for relevant clinical trials. The records were screened for eligibility. Data were extracted from the included studies. Outcomes were pooled as risk ratios (RR) or mean differences with 95% CIs using RevMan ver.5.4. Our study included 13 randomized clinical trials with 735 patients. Our analysis revealed that endoscopic septoplasty was significantly (P<0.05) superior to conventional septoplasty for postoperative nasal obstruction relief, intraoperative and postoperative hemorrhage, and mucosal adhesion and synechiae across both long-term and short-term follow-ups. The following pooled RR values were found in short-term follow-up periods: [RR=1.20, 95% CI:=(1.09,1.32)]; [RR=0.27, 95% CI=(0.14,0.54)]; and [RR=0.16, 95% CI=(0.08,0.32)], respectively. Regarding persistent septal deviation and septal tear, endoscopic septoplasty had the upper hand only in short-term follow-up periods [RR=0.30, 95% CI=(0.17,0.53)] and [RR=0.26, 95% CI=(0.15,0.46)], respectively. Our analysis revealed that endoscopic septoplasty was significantly superior to conventional septoplasty in postoperative nasal obstruction relief rate and reducing the risk of intraoperative and postoperative hemorrhage, mucosal adhesion and synechiae, persistent septal deviation, septal tear, and surgery duration.

Causes and management of persistent septal deviation after septoplasty

Septoplasty is one of the most common otolaryngological surgical procedures. The causes of persistent septal deviation after primary septoplasty vary. The purpose of this study was to identify factors associated with failure of primary septoplasty, operative techniques that correct residual septal deviation, and surgical outcomes. Seventy-four adults who underwent revision septoplasty to treat persistent septal deviations were enrolled. The level of hospital in which primary septoplasty was performed, type of septal deviation, septal portion exhibiting persistent deviation, and techniques used to correct the deviation were evaluated. Outcomes were measured subjectively using a visual analog scale (VAS), and objectively using acoustic rhinometry. The first septoplasties were usually performed in primary and secondary hospitals. C-shaped deviations were more common than S-shaped ones in both the anteroposterior and cephalocaudal dimensions. The most common region of persistent septal deviation was the caudal septum (44.6%), followed by multiple sites (20.3%). The corrective techniques included excision of the remnant deviated portion (70.3%), septal cartilage traction suturing (27.0%), spreader grafting (13.5%), and cross-suturing (6.8%). The VAS score improved significantly 6 months after surgery. The minimal cross-sectional area and nasal cavity volume of the convex side increased significantly after revision septoplasty. Patients who underwent septoplasty in primary and secondary hospitals were more likely to require revision septoplasty. The caudal septum was the most common site of persistent septal deviation. Careful preoperative evaluation of the caudal septal deviation and selection of an appropriate surgical technique may reduce the need for revision septoplasty.

Functional Brain Asymmetry and Menopausal Treatments: Is There a Link?

Background and Objectives: The human brain presents a functional asymmetry for every cognitive function, and it is possible that sexual hormones could have an impact on it. Visual–spatial attention, one of the most lateralized functions and one that is mainly dependent on the right hemisphere, represents a sentinel for functional cerebral asymmetry (FCA). The aim of this study was to evaluate whether menopausal hormone therapy (MHT) or phytoestrogens could modulate FCA in postmenopausal women. Materials and Methods: We enrolled postmenopausal women who were taking MHT or soy isoflavones or receiving no therapy and asked them to perform the line bisection test at study enrollment and after 18 and 36 months. Results: Ninety women completed the follow-up. At zero time, women who had not been subjected to therapy showed a leftward deviation (F = −3.0), whereas, after 36 months, the test results showed a rightward deviation (F = 4.5; p < 0.01). Women taking MHT showed a leftward deviation at the start (F = −3.0) and a persistent leftward deviation after 36 months (F = −4.0; p = 0.08). Conversely, women taking soy isoflavones started with a leftward deviation (F = −3.0) that became rightward (F = 3.0), with a significant difference shown after 36 months (p < 0.01). Conclusions: Our data suggest that hormonal modulation improves the interplay between the two hemispheres and reduces FCA. We propose, therefore, that the functions of the right hemisphere are mainly affected by aging and that this could be one of the reasons why the right hemisphere is more susceptible to the effects of MHT.

U.S. Dollar Currency Premium in Corporate Bonds

We isolate a U.S. dollar currency premium by comparing corporate bonds issued in the dollar and the euro by firms o utside t he U .S. a nd e uro a rea. We make s everal empirical observations that dissect the perceived advantage of borrowing in the dollar. First, while the dollar dominates global debt issuance, borrowing costs in the dollar are more expensive without a currency hedge and about the same with a currency hedge when compared to the euro. This observed parity in currency-hedged corporate borrowing stands in contrast to the persistent deviation from covered interest parity in risk-free rates. Second, we observe a dollar safety premium in relative hedged borrowing costs, found in the subset of bonds with high credit ratings and short maturities, attributes similar to those of safe sovereigns. Finally, we find that firms flexibly adjust the currency mix of their debt issuance depending on the relative borrowing cost between dollar and euro debt. In sum, the disproportionate demand for U.S. dollar debt is reflected in higher issuance volumes that drive up the currency hedged dollar borrowing costs such that at the margin they equate to euro borrowing costs.

Diarrhea when COVID-19 in adults

This review provides a systematization of literature on the problem of chronic diarrhea in adults, issues of differential diagnosis and diagnosis at the stage of primary health care Chronic diarrhea is a persistent deviation from the norm with the consistency of stool between types 5 and 7 on the Bristol stool scale and an increase in frequency of more than 4 weeks. The classification of diarrhea in terms of frequency (the most common causes, infrequent and rare), a brief description of clinical and laboratory signs of the most common causes of diarrhea in the practice of a General practitioner and gastroenterologist, a review of the literature on the features of diarrhea in COVID-19, and the stages of diagnostic search.

Methodology for the Application of Nonparametric Control Charts into Practice

Classical parametric statistical methods are based on several basic assumptions about data (normality, independence, constant mean and variance). Unfortunately, these assumptions are not always fulfilled in practice, whether due to problems arising during manufacturing or because these properties are not typical for some processes. Either way, when we apply parametric methods to such data, whether Shewhart’s or other types of parametric control charts, it is not guaranteed that they will provide the right results. For these cases, reliable nonparametric statistical methods were developed, which are not affected by breaking assumptions about the data. Nonparametric methods try to provide suitable procedures to replace commonly used parametric statistical methods. The aim of this paper is to introduce the reader to an alternative way of evaluating the statistical stability of the process, in cases where the basic assumptions about the data are not met. First, possible deviations from the data assumptions that must be met in order to use classical Shewhart control charts were defined. Subsequently, simulations were performed to determine which nonparametric control chart was better suited for which type of data assumption violation. First, simulations were performed for the in-control process. Then simulations for an out-of-control process were performed. This is for situations with an isolated and persistent deviation. Based on the performed simulations, flow charts were created. These flow charts give the reader an overview of the possibilities of using nonparametric control charts in various situations. Based on the performed simulations and subsequent verification of the methodology on real data, it was found that nonparametric control charts are a suitable alternative to the standard Shewhart control charts in cases where the basic assumptions about the data are not met.

A comparative study of endoscopic versus conventional septoplasty

&lt;p class="abstract"&gt;&lt;strong&gt;Background:&lt;/strong&gt; Deviated nasal septum is one of the common causes of nasal obstruction. Correction of deviated nasal septum has been performed by a variety of techniques of which Septoplasty is the most popular one. With the advent of endoscopes and their successful use in endoscopic sinus surgery endoscopes have been tried in septoplasty for better visualization of posterior part of septum and do the surgery more precisely and with less complication as compare to conventional method. The objectives of the study were to compare the outcomes of conventional and endoscopic septoplasty, to evaluate the advantages, disadvantages and complications of both endoscopic and conventional septoplasty.&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Methods:&lt;/strong&gt; It was a prospective observational study conducted on 50 patients with deviated nasal septum, who presented to ENT department of SPMC, Bikaner, patients were randomly divided equally in two groups for conventional and endoscopic septoplasty respectively. Data collected on a prestructured proforma and results analysed. &lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Results:&lt;/strong&gt; The study included 50 cases. Postoperatively significant relief from the symptoms of nasal obstruction (82%) in group A and (96%) group B, was seen. In objective assessment at the end of 3 months of surgery, patient had persistent posterior deviation 24% in group A and 3% in group B, spur 12% in group A and 0% in group B.&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Conclusions:&lt;/strong&gt; Endoscopic septoplasty has an obvious edge over the conventional approach due to better illumination which enables to identify the pathology accurately, excise the deviated part of septum precisely and realignment of the cartilage for best results.&lt;/p&gt;

ЗАСТОСУВАННЯ МЕТОДІВ ОБРОБКИ ПРИРОДНОЇ МОВИ ДЛЯ ВИЯВЛЕННЯ СИМПТОМІВ МЕНТАЛЬНОГО ЗАХВОРЮВАННЯ

Здійснено порівняльний аналіз різних методів оброблення природної мови для виявлення симптомів ментального захворювання. Розглянуто принцип роботи та ефективність моделей оцінювання семантичної когерентності тексту (моделі тан-генційності та некогерентності) для класифікації текстів здорових і хворих осіб. У роботі зазначається залежність точності моделей некогерентності та тангенційності від моделі семантичного представлення фрагментів тексту; підкреслюється недолік використання такої моделі в зв'язку з відсутністю можливості враховувати регулярне повторення фраз. Проаналізовано переваги та недоліки застосування комбінації моделей семантичного представлення елементів тексту для врахування постійних повторів його фрагментів. Обґрунтовано доцільність застосування лінгвістичних характеристик тексту пацієнта для підвищення точності класифікаторів виявлення симптомів захворювань та розрізнення їх типу. Розглянуто можливість аналізу частоти появи неоднозначних займенників у тексті для підвищення точності класифікації даних. Проаналізовано особливості застосування різних методів виявлення симптомів ментального захворювання для текстів англійською, німецькою та російською мовами. Запропоновано здійснювати оцінювання зв'язності тексту за допомогою графу узгодженості словосполучень. Здійснено експериментальну перевірку ефективності пропонованого підходу для побудови класифікаційної моделі порівняно з іншими характеристиками тексту.

Stress-Drop and Source Scaling of the 2019 Ridgecrest, California, Earthquake Sequence

ABSTRACTStress drop, while difficult to measure reliably and at scale, is a key source parameter for understanding the earthquake rupture process and its relationship to strong ground motion. Here, we use a P-wave spectral decomposition approach, designed for large and densely sampled datasets, to measure earthquake stress drop in the region surrounding the 2019 Ridgecrest, California, earthquake sequence. With more than 11,000 measurements of earthquake stress drop in the 20-yr time period from 2000 through 2019, this dataset provides an opportunity to understand how coseismic stress changes and how other geophysical factors relate to the distribution of stress drop and its evolution in space and time. We observe a mild but persistent deviation from self-similar scaling, with larger events having systematically higher stress drops, though this trend depends on the assumption of an omega-square source spectral model. Earthquake stress drop increases with hypocentral depth in this study region, and the Ridgecrest aftershocks tend to have higher stress drops than the pre-event seismicity. This is in part due to their deeper hypocenters. Coherent spatial patterns of stress drop in the aftershock sequence correlate with the slip distribution of the M 7.1 mainshock, whose northwest rupture tip terminated in a long-lived zone of enervated stress drop. Although physical interpretation of these results is complicated by the trade-offs between the timing, depth, and location of these earthquakes, the observations provide new insight into the physics of the earthquake source in an area of renewed seismic activity in southern California.

The Link Between Social Determinants of Health, Sleep, and Cardiovascular Disease

Chronic sleep insufficiency or long-sleep duration appears to contribute to the development of cardiovascular disease (CVD) and other related metabolic conditions, including obesity and type 2 diabetes mellitus. Emerging evidence suggests that effective treatment of a sleep disorder may prevent subsequent cardiovascular events. Therefore, promotion of optimal sleep and the identification and adequate treatment of sleep disorders earlier in life may prevent or reduce the risk of CVD and the subsequent consequences of CVD. Promotion of optimal health behaviors, including sleep health, need to consider how social determinants of health (SDOH) influence and affect the ability of individuals to adequately and effectively incorporate health behavior recommendations into their daily lives. Therefore, the purpose of this perspective article is to (1) discuss how persistent deviation from the recommended amount and quality of sleep contributes to the development of CVD; and (2) discuss how SDOH across the levels of the Social–Ecological Model influence sleep health and potentially CVD.

Clinical findings and surgical outcomes of patients with traumatic isolated inferior rectus muscle paresis

To evaluate clinical findings and surgical outcomes of patients with traumatic isolated inferior rectus muscle paresis. The medical records of patients with traumatic isolated inferior rectus paresis who underwent strabismus surgery at Farabi Eye Hospital between 2011 and 2018 were reviewed retrospectively. Clinical features, type of surgery, and surgical outcomes were extracted from the record for analysis. A total of 19 patients (14 males [74%]) were included. Mean patient age was 34.8±14.6years. Left eyes in 13 patients (68%) were involved. Thirteen cases (68%) underwent orbital reconstruction surgery for blow-out fracture. Preoperative limitation of duction in the gaze of the inferior rectus muscle was -2 to -3 in all cases. Four patients (21%) had a paradoxical contralateral compensatory head tilt. Inferior rectus muscle resection alone was the first surgical intervention in 12 patients (63%). At the final follow-up, 12 patients (63%) were orthotropic, without any deviation or diplopia in primary position and downgaze. Three patients (16%) had a residual hypertropia of 3Δ at distance and near without diplopia, and 4 patients (21%) required reoperation. In our patients with traumatic isolated inferior rectus paresis with persistent deviation at least 6months after trauma, a stepwise approach based on size of the vertical deviation was employed, with good outcomes: inferior rectus resection alone for hypertropia of 6Δ-20Δ and inferior rectus resection and superior rectus recession for hypertropia of ≥20Δ or significant hypertropia in the field of the superior rectus muscle.

Cases of aadc deficiency need detection as a treatable cause of dystonia and persistent upward deviation of eyes masquerading as seizures

Cases of aadc deficiency need detection as a treatable cause of dystonia and persistent upward deviation of eyes masquerading as seizures

Factors Associated With Reoperation After Silicone Proximal Interphalangeal Joint Arthroplasty.

Background: Silicone proximal interphalangeal (PIP) joint arthroplasty has a high revision rate. It has been suggested that persistent ulnar deviation and joint instability influence the durability of PIP silicone arthroplasties. The goal of this study was to evaluate what factors are associated with reoperation after silicone PIP arthroplasty. Methods: We retrospectively evaluated all adult patients who underwent PIP silicone arthroplasty between 2002 and 2016 at one institutional system for inflammatory-, posttraumatic-, and primary degenerative arthritis. After manual chart review, we included 91 patients who underwent 114 arthroplasties. Fingers operated included 14 index, 41 middle, 38 ring, and 21 small fingers. Results: The overall reoperation rate was 14% (n = 16). Non-Caucasian race (P = .040), smoking (P = .022) and PIP silicone arthroplasty for post-traumatic osteoarthritis (P = .021) were associated with reoperation. The 1-, 5- and 10-year implant survival rates were 87%, 85%, and 85%, respectively. Conclusion: Caution should be exercised when considering PIP silicone arthroplasty of the index finger or in patients with post-traumatic osteoarthritis. It may be worthwhile addressing smoking behavior before pursuing silicone PIP arthroplasty.

Common Sites, Etiology, and Solutions of Persistent Septal Deviation in Revision Septoplasty.

ObjectivesTo investigate the common causes of persistent septal deviation in revision septoplasty and to report the surgical techniques and results to correct them.MethodsA total of 100 consecutive patients (86 males) who had revision septoplasty due to persistent septal deviation from 2008 and 2014 were included in the study. Their mean age was 35.6 years and the mean follow-up duration was 9.1 months. Presenting symptoms, sites of persistent septal deviation, techniques used to correct the deviation, and surgical results were reviewed.ResultsThe mean interval between primary and revision surgery was 6.2 years. Forty-eight patients received revision septoplasty and 52 received revision septoplasty combined with rhinoplasty. Nasal obstruction was the most presenting symptom in almost all patients. The most common site of persistent septal deviation was middle septum (58%) followed by caudal septum (31%). Correcting techniques included further chondrotomy and excision of deviated portion in 76% and caudal batten graft in 39%. Rhinoscopic and endoscopic exams showed straight septum in 97% and 92 patients had subjective symptom improvement postoperatively.ConclusionMiddle septum and caudal septum were common sites of persistent deviation. Proper chondrotomy with excision of deviated middle septum and correction of the caudal deviation with batten graft are key maneuvers to treat persistent deviation.

The Selection of the Formation Mechanism of Expectation, the Mix of Macro-policy and the Management of Inflation Expectation

Based on the reality of macro-policy in China, this paper analyzes the effect of the formation mechanism of expectation on the mix of macro-policy and the management of inflation expectation. The results show that dynamic stochastic general equilibrium model based on learning expectation not only portrays the trend consistency and persistent deviation between expected inflation and real inflation, but also demonstrates the changes in the price expectation index published by the people's Bank of China and the index of consumer expectations announced by the National Bureau of Statistic. From a perspective of the management of inflation expectation, the mix of monetary policy and fiscal policy is affected not only by economic fundamental factors, but also by the formation mechanism of expectation, and should shift from traditional loose-tight mode to two-tight or two-loose modes. Under the current situation, macro policy should focus on directional control based on precision guidance, strengthen the reform of economic system, and improve the supply side of economic system to match the demand side and lock the policy target. Meanwhile, by active communication, our government should shape and stabilize the macro-policy expectation of the public, and enlarge the policy adjustment space to achieve steady economic growth.

Making sense of common Dirichlet deviations

This paper reviews the regularly recurring deviations between buyer behaviour patterns and predictions from the NBD-Dirichlet model. Previous studies have tended to look at one or two Dirichlet Deviations in isolation; the aim here is to learn more about their managerial significance by categorising them according to their behavioural indicators, summarising their incidence and extent and relating them to the implied breaches of assumptions of the model. We replicate prior research results in a single, extensive database of 62 FMCG categories and find that the Dirichlet Deviations take three forms; slight systematic variances in expected metrics across all brands in every fitting, suggesting some failure in stationarity; certain types of persistent deviation for individual brands or groups of brands that indicate partitioning; and those that capture dynamic performance. Analysis shows that consumer purchase propensities are never quite fixed or entirely independent, yet brand performance remains close to Dirichlet prediction. Managers who use this model need to be aware of the strategic options that the deviations imply, and we discuss these. Findings also contribute to the idea that deviations might be reduced by model adaptations although the managerial simplicity of the NBD-Dirichlet sets a major challenge to this.