Secular Changes Research Articles

The Quadratic-Exponential-Pubertal-Stop model is valid for analysing human growth patterns and developing novel growth references.

Human growth patterns are important, especially in paediatrics and public health, and the aim of this review was to provide an overview of human growth, especially secular changes of growth and pubertal growth. This review of human growth was mainly based on studies published during the 20th and early 21st centuries. Special attention was paid to secular changes, pubertal growth, Nordic growth studies and the contribution of the Quadratic-Exponential-Pubertal-Stop (QEPS) growth model for analysing growth patterns. Human growth patterns showed wide variations between different individuals, sexes and populations and over time. There were ongoing positive secular change in height in four of the Nordic countries, Denmark, Finland, Norway and Sweden, over four decades. Childhood weight status had linear correlations with specific pubertal growth, in both healthy children and those with severe obesity. The QEPS model provided novel estimates of pubertal growth that made it possible to conduct more detailed analyses of pubertal growth than before. Growth references, adjusted for puberty, have been developed, and future opportunities for using the QEPS model for growth studies are highlighted. The QEPS was a valid growth model for analysing human growth patterns and developing novel types of growth references.

A Magnetospheric Dichotomy for Pulsars with Extreme Inclinations

In this work, we expand on a comment by Lyne et al. (2017), that intermittent pulsars tend to congregate near a stripe in the logarithmic period versus period-derivative diagram. Such a stripe represents a small range of polar cap electric potential. Taking into account also the fact (already apparent in their Figure 7, but not explicitly stated there) that high-fraction nulling pulsars also tend to reside within this and an additional stripe, we make the observation that the two stripes further match the “death lines” for double- and single-pole interpulses, associated with nearly orthogonal and aligned rotators, respectively. These extreme inclinations are known to suffer from pair production deficiencies, so we propose to explain intermittency and high-fraction nulling by reinvigorating some older quiescent (no pulsar wind or radio emission) “electrosphere” solutions. Specifically, as the polar potential drops below the two threshold bands (i.e., the two stripes), corresponding to the aligned and orthogonal rotators, their respective magnetospheres transition from being of the active pair-production-sustained-type into becoming the electrospheres, in which charges are only lifted from the star. The borderline cases sitting in the gap outside of the stable regime of either case manifest as high-fraction nullers. Hall evolution of the magnetic field inside orthogonally rotating neutron stars can furthermore drive secular regime changes, resulting in intermittent pulsars.

Home Improvement: Evaluating Secular Changes in NLSY HOME-Cognitive Stimulation and Emotional Support Scores.

This study evaluated changes over time in the quality of children’s home environment, using the Home Observation Measurement of the Environment (HOME). Longitudinal increases in HOME scores were predicted by both theory and past empirical results. Analysis of the National Longitudinal Survey of Youth Children data (N = 5715, aged 0–14) suggested that HOME scores have been increasing, and that the increase is a family-level phenomenon. The data were a sample of children born to mothers who were approximately representative of the United States in 1979. An increase in HOME scores occurred primarily for the three age categories younger than ten. Effect sizes were of approximately the same magnitude as the Flynn effect for intelligence. These results have implications for policy and future research regarding the home environment.

Urban versus rural differences of hip fractures among the elderly in Kyoto, Japan: a 10-year study.

Our survey in Kyoto Prefecture from 2008 to 2017 showed that the incidence rate of femoral neck fractures is generally increasing. We investigated the differences between urban and rural areas in the changes of the incidence rate over time of femoral neck and trochanteric fractures during the same period. Patients aged 65years and above who sustained hip fractures between 2008 and 2017 and were treated at one of the participating 11 hospitals were included. The ratio of sick beds for acute-term care at the investigated hospitals to total number of beds in the urban area was 16.5% (1863/11,158) and 30.6% (1863/5623) in the rural area. The change in incidence rate was estimated utilizing the population according to the national census conducted in 2010 and 2015. There were 3559 and 6474 hip fractures in the urban and rural areas, respectively. Femoral neck fractures were 1936 (54.4%) and 2813 (43.5%) in each area. The increase of the population-adjusted numbers was marked by neck fractures in males, in both areas. In women, there was a significant increase in femoral neck fractures in the urban area in those aged 85years and over. For trochanteric fractures, a significant increase was only found in women aged 65 to 74years in the rural area. A regional difference in the secular changes in incidence rate of hip fractures was found in women, not in men, mostly because neck fractures in women increased in the over 85 group in the urban area.

The interplay of environmental constraints and bioturbation on matground development along the marine depositional profile during the Ordovician Radiation.

This study documents the distribution of matgrounds in a wide variety of environments recorded in the Ordovician Lashkerak and Ghelli Formations in the Alborz Mountains of northern Iran in order to evaluate controls on their distribution along the marine depositional profile. Detailed facies analysis allowed differentiating three groups of facies associations in the Lower to Upper Ordovician deposits of the Lashkerak formation: (i) estuarine system; (ii) wave-dominated shoreface-offshore complex; and (iii) mixed river- and wave-influenced deltaic system. The Middle to Upper Ordovician deposits of the Ghelli formation are divided into two groups of facies associations: (i) tide-influenced deltaic succession and (ii) deep-water fan system. Microbially induced sedimentary structures (MISS) are present in deposits formed in the central estuarine basin (Lashkerak formation) and in proximal lobes and lobe fringes of deep-water turbidite fans (Ghelli formation). On the contrary, MISS are absent in deposits from the wave-dominated shoreface-offshore complex, river- and tide-dominated deltas, and various subenvironments of the incised wave-dominated estuary (i.e., bayhead delta and estuary mouth) and the deep-marine turbidite fan system (i.e., turbidite channel, slope, and outer lobe). The lack of evidence of mat-building microorganisms in the deltaic systems may have resulted from two factors: (1) high physico-chemical stressors caused by river-induced processes, and (2) increase in degree of sediment disturbance, biodiffusion, and bioirrigation by burrowing organisms. Formation of microbial mats in the wave-dominated shoreface-offshore complex was inhibited by the activity of an abundant and diverse infauna capable of reworking the sediment. Our analysis shows that the spatial distribution of microbial mats was controlled by an interplay of environmental factors and innovations in animal-substrate interactions, mostly expressed by secular changes in bioturbation. This study supports the notion that the agronomic revolution was diachronic, with marginal-marine and deep-sea ecosystems lagging behind shallow-marine settings.

Do Maya women have the chance to improve their quality of life?

Background: Maya families suffered greatly during the henequen industry in the Yucatan, but the lives of the Maya women at the time were perhaps worse than anywhere in the world. Changes in Maya body height over the 20th century were assessed in order to show secular changes. The use of the sexual dimorphism index (SDI) allowed for the evaluation of the living conditions prevailing during the existence of the henequen haciendas to the Mexican revolution and a gradual improvement of these conditions by the end of the 20th century. Methods: In 1994, 364 men and 320 women aged 20-98 years were studied in Merida, Yucatan, Mexico. They were divided into six age groups and by gender: 20-29, 30-39, 40-49, 50-59, 60-69 and 70+ years. Stature for both genders, and age at menarche for women were considered. SDI in stature was calculated to assess living conditions. Results: There were smaller (0.25 cm/10 years) changes in height in men than in women (0.9 cm/10 years) and no significant changes in acceleration of maturation. SDI results showed changes from 9.9 to 7.6, and this may indicate a constant, but very small improvement of living conditions. The age at menarche of women did not show statistically significant acceleration with age. Conclusions: In the colonial period of the late 19th century until the Mexican Revolution, women were worse off than men. Previous research has shown that when living conditions change, men always react faster than women, e.g. by lowering or increasing body height. Our study of the Maya population in the 20th century showed otherwise; female height increased more than male height. This may reflect that the living conditions of Maya men have not changed over the 20th century, but have improved for women.

S1201 Age-Adjusted Mortality Rates of Liver-Related Death in a VA Cohort of Patients With Cirrhosis

Introduction: Direct-acting antiviral (DAA) therapy for hepatitis C reduces the risk of decompensation and hepatocellular carcinoma among patients with cirrhosis. Long-term population-based data quantifying the effect of DAAs on cause-specific mortality in cirrhosis remain lacking. The aim of this study was to evaluate temporal trends in overall and cause-specific mortality in a national cohort of patients with cirrhosis. Methods: We performed a retrospective cohort study of patients with cirrhosis diagnosed between 2008-2017 in the Veterans Health administration. We determined cause of death from the Mortality Death Registry and characterized these as following: all-cause mortality, mortality related to liver disease (including liver neoplasm, end-stage liver disease, infection, and GI hemorrhage), and mortality due to liver neoplasm only. Age-adjusted mortality rates, annual adjusted percent change (AAPC) in mortality rate, and inflection points (Joinpoints) were calculated using the SEER*Stat Joinpoint regression program referencing a standard population from US Census data. Results: 129,700 male patients with cirrhosis were included, 75% related to hepatitis C infection; 20.3% of the total population died during the follow-up period. All-cause mortality declined between 2008-2017, with a change in AAPC rate detected in 2015 from -2.57% to -6.93% (Figure). Similarly, composite liver mortality declined throughout the study period but accelerated after 2013 from -3.09% to -10.2%. By contrast, liver neoplasm-related mortality increased until 2012 (+0.72%), then declined after 2013 (-8.14%). Conclusion: Sharp declines in liver-related death appear to precede the widespread availability of all-oral DAA therapy by about one year suggesting significant impacts of improved general and HCC-related liver care. Both liver neoplasm-related death and composite liver mortality (including liver cancer) decreased significantly after 2013, likely due to secular changes in liver cancer care and improved management of decompensated liver disease. Overall mortality, however, decreased significantly after 2015, most likely due to increased availability of direct-acting antiviral (DAA) agents for hepatitis C. Data should be confirmed in a non-veteran population.Figure 1.: Age-Adjusted Total, Liver-Neoplasm, and Liver Composite Mortality Rates, 2008-2017.

静岡県・清水海岸中央部における海岸侵食—空中写真からみた経年変化と台風前後の海岸変形—

静岡県・清水海岸中央部における海岸侵食—空中写真からみた経年変化と台風前後の海岸変形—

Secular trend in skeletal growth among urban Japanese during the Edo period (1603–1867)

ObjectiveThe present study aims to investigate whether any secular change in growth occurred among the urban populations during the Edo period (1603–1867). During this time, the preconditions for industrialization were established through rapid urbanization, population increase, and economic development. MaterialsNinety subadult and 189 adult skeletal remains were recovered from eight Edo-period burial sites in Tokyo were examined. MethodsMaximum femoral lengths were measured and compared between the early and late Edo periods. ResultsWhile subadults of the late Edo period—especially of higher status—tended to have longer femoral lengths, the adult males tended to have slightly shorter femoral lengths. No clear difference was found among adult females. ConclusionsThere was no clear or consistent secular change in growth patterns or in adult stature. The impact of social and economic transformations in 17th-century Japan on growth and on general health status remains unclear. SignificanceThis is the first study to examine the impact of social changes on growth immediately before the industrialization of Japan. It will be helpfull to understand the complex relationship between human growth and social changes. LimitationsChanges in growth patterns may have been obscured by the small sample size, errors in estimating age and femoral lengths, temporary changes in growth in the late Edo period, or catch-up growth. Suggestions for Further ResearchRe-examining with a larger sample, introducing more precise dating of burials and more precise age estimation methods, and examining multiple physiological stress indicators are necessary.

Coupled Model Intercomparison Project phase 6 evaluation and projection of East African precipitation

AbstractThis study evaluates the performance of 43 Coupled Model Intercomparison Project phase 6 (CMIP6) models in reproducing annual cycle, climatology, and trend of observed precipitation over East Africa during 1950–2014. The results show that the CMIP6 models display good performance in simulating the annual cycle (i.e., bimodal pattern) of East African precipitation; however, most models and the multimodel ensemble mean (ENSEM) underestimate the March to May (MAM) precipitation while overestimating the October to December (OND) precipitation. Spatially, most models seem to perform relatively better in simulating OND precipitation compared to MAM season, despite wet (dry) biases over most parts of East Africa with the wettest (driest) biases over the Lake Victoria basin (southeastern Tanzania) during OND (MAM). The metrics have shown that nine models (i.e., MPI‐ESM1‐2‐HR, AWI‐CM‐1‐MR, MPI‐ESM1‐2‐LR, IPSL‐CM6A‐LR, CAS‐ESM2‐0, BCC‐CSM2‐MR, NorESM2‐LM, CESM2‐WACCM, and CMCC‐CM2‐SR5) outperform the other individual models during both OND and MAM. Compared with individual models, the ENSEM better agrees with the observation. Besides, the ENSEM and most models can reproduce the increasing trend in OND precipitation as observed over East Africa. However, for the secular change of MAM precipitation, given that half of the models show increasing trends, the ENSEM simulation produces an inconsistent trend with the observation. The ensemble of the above nine models with better performance projects an increase of precipitation averaged over East Africa in both MAM and OND by the end of the 21st century, with larger changes under SSP5‐8.5 than under SSP2‐4.5. Spatially, the largest percentage increase in MAM precipitation is projected to occur in central Tanzania and northwestern Kenya, while southeastern Tanzania shows the greatest percentage decrease. The projected percentage increases in OND precipitation are larger in the northeastern highlands of Tanzania and northwest Kenya.

Historical and Recent Changes in Maternal Mortality Due to Hypertensive Disorders in the United States, 1979 to 2018.

[Figure: see text].

Validation of algorithms using International Classification of Diseases for the identification of herpes zoster episodes requiring hospitalization in Quebec, Canada

ObjectiveWe determined secular changes in the incidence of hospitalizations due to herpes zoster (HZh) and assessed the validity of HZ International Classification of Diseases (ICD) code algorithms for identifying HZh in a region of Quebec, Canada. MethodsWe performed a validation study as part of a retrospective cohort study of adult HZ patients hospitalized at Centre Hospitalier Universitaire de Sherbrooke during 2000–2017. Cases were identified using ICD codes from an inpatient administrative database. HZ cases identified by ICD-9 (053.xx) and ICD-10 (B02.x) codes were chart-confirmed, and performance characteristics of ICD code algorithms were calculated (positive predictive value [PPV] and sensitivity). ResultsOverall, 1314 hospitalizations with HZ diagnosis (HZh) with or without complications were identified during 2000–2017. Among the hospitalizations, 526 (44.4%) were due to active HZ disease or a complication related to a recent or previous HZ episode. These hospitalizations were due to active disease at the time of admission (340/526, 64.6%), HZ that developed during hospitalization (120/526, 22.8%), or a complication directly related to a recent or previous HZ episode (66/526, 12.6%). PPV was significantly higher when HZ was the primary diagnosis (276/310, 89%, 95% confidence interval [CI]: 85–92%) than when HZ was a secondary diagnosis (254/928, 27%, 95% CI: 25–30%) (p < 0.0001), and the PPV of a first secondary diagnosis (84/140, 60.0%, 95% CI: 51.3–68.2%) was higher than that of other secondary diagnoses (203/794, 25.6%, 95% CI: 22.6–28.8%) (p < 0.0001). An algorithm combining ICD codes and antiviral usage demonstrated the best sensitivity (86.3%, 95% CI: 83.1–89.1%) and PPV to identify HZh (100%, 95% CI: 99.2–100%). Poisson regression revealed no significant changes in HZh over time (incidence rate ratio: 0.98, 95% CI: 0.92–1.04%; p = 0.5). ConclusionHZh incidence was stable over time. Prescription of antivirals might be a useful addition to ICD codes to identify HZh cases from administrative databases.

Social inequalities in obesity and overweight: secular changes in Poland between 1983 and 2020.

Human development is strongly influenced by environmental factors, including the socioeconomic status (SES) of the family. The aim of this study is to analyze the prevalence of excess body weight among Polish children and adolescents from families of varying SES examined in 1983 and 2020. The study group included 3-15-year olds from two cross-sectional surveys (1983 and 2020) conducted in kindergartens and schools. The 1983 cohort consisted of 3394 individuals and the one from 2020-of 1253 children and adolescents. Body height and weight were measured and body mass index was calculated. Inclusion into underweight, normal weight and overweight/obese categories was based on Cole's cutoff points. SES was established based on the place of the parents' birth, parents', education status and the number of children in the family, which were self-reported in a questionary by the parents of the examined individuals. The mean overall SES was higher in the 2020 cohort, in comparison to the one examined in 1983. This change was also reflected by the changing prevalence of excess body weight, which, in 1983 was the greatest in the high socioeconomic category. On the other hand, in 2020 overweight/obesity was the most prevalent among individuals from families of low SES. The present results confirm the findings obtained in other countries, which suggest that changing the level of socioeconomic development modifies the changes regarding the prevalence of excess body weight. It is an important observation because a study of this type has not yet been conducted in the Polish population.

Estimation of Pubertal Growth Spurt Parameters in Children and Adolescents Living at Moderate Altitude in Colombia.

ObjectiveKnowledge of the biological parameters of pubertal growth spurt allows verification of secular changes and exploration of the timing of puberty. The aim of the study was to estimate final height, age at peak height velocity (APHV), and peak height velocity PHV (cm/y) in children and adolescents living at moderate altitude in Colombia.MethodsA cross-sectional study was designed in 2.295 schoolchildren from Bogotá (Colombia) with an age range from 5.0 to 18.9 years. Height (cm) was assessed. Preece–Baines model 1 (1PB) was used to make inferences about mathematical and biological parameters.ResultsThe five mathematical parameters estimated in general have reflected quality in the fit to the model, reflecting a small residual error. Final height was reached in boys at 170.8 ± 0.4 cm and in girls at 157.9 ± 0.2 cm. APHV was estimated at 12.71 ± 0.1 years in boys and 10.4 ± 0.2 years in girls. Girls reached APHV 2.2 years earlier than boys. In relation to PHV (cm/y), boys reached higher growth speed in height (7.4 ± 0.4 cm/y), and in girls it was (7.0 ± 0.2 cm/y).ConclusionIt was determined that final height was reached at 170.8 ± 0.4 cm in boys and 157.9 ± 0.2 cm in girls, and APHV (years) and PHV (cm/ye) were reached relatively early and with average peak velocity similar to Asian and Western populations. A large-scale longitudinal study is needed to confirm these findings.

Changes in Tornado Climatology Accompanying the Enhanced Fujita Scale

AbstractUnited States tornado records form the basis for a variety of meteorological, climatological and disaster-risk analyses, but how reliable are they in light of changing standards for rating, as with the 2007 transition of Fujita (F) to Enhanced Fujita (EF) damage scales? To what extent are recorded tornado metrics subject to such influences that may be nonmeteorological in nature? While addressing these questions with utmost thoroughness is too large of a task for any one study, and may not be possible given the many variables and uncertainties involved, some variables that are recorded in large samples are ripe for new examination. We assess basic tornado-path characteristics—damage rating, length, width, and occurrence time, as well as some combined and derived measures—for a 24-yr period of constant path-width recording standard that also coincides with National Weather Service modernization and the WSR-88D deployment era. The middle of that period (in both time and approximate tornado counts) crosses the official switch from F to EF. At least minor shifts in all assessed path variables are associated directly with that change, contrary to the intent of EF implementation. Major and essentially stepwise expansion of tornadic path widths occurred immediately upon EF usage, and widths have expanded still further within the EF era. We also document lesser increases in path lengths, and in tornadoes rated at least EF1 compared to EF0. These apparently secular changes in the tornado data can impact research dependent on bulk tornado-path characteristics and damage-assessment results.

Secular changes in human reproduction and assisted reproductive technologies

Since the middle to late 20th century the majority of children born in the developing world have been likely to enter into post-reproductive age. Currently, child mortality is at its lowest level in human history. While more children are living to post reproductive age, approximately 15% of couples are experiencing infecundity. This is either a result of one or both members of the couple being infecund, or, despite both being fecund, the interaction between them prevents fertility for some reason. Assisted reproductive technologies have provided many infertile couples an opportunity to have children. Assisted reproductive technologies operate by intervening and manipulating gametic and intrauterine natural selection. This paper discusses the possible influence of assisted reproductive technologies on child development. This paper outlines some of the reported changes in children resulting from assisted reproductive technologies. Although, few people are either aware or care about possible long term consequences of relaxed natural selection contributed by medical intervention (i.e. assisted reproductive technologies) we have little understanding to what extent such medical interference may affect long term fitness in humans.

Signs of a new geomagnetic jerk between 2019 and 2020 from Swarm and observatory data

Following the observed pattern of a new geomagnetic jerk every 3–4 years, certain predictions suggested that a new event should occur around 2020 after the one observed around 2017.5. In this work, we explore this scenario by analysing the secular variation of the East geomagnetic field component in both ground and satellite geomagnetic data. At ground, we use the available data from 2015 to 2021 in 10 observatories worldwide distributed. This analysis shows the occurrence of the mentioned jerk in mid-2017 at observatories located in the Pacific region, but also reveals a new jerk between mid-2019 and early 2020 with a clear global character. Swarm satellite data also corroborate these findings by means of the secular variation estimated using virtual observatories at 440 km altitude. In addition, a general view using the most recent CHAOS geomagnetic model confirms the global character of the 2020-jerk with V-shaped secular variation changes in meridional sectors covering the Eastern Pacific, America, Asia and the Indian Ocean; and Λ-shapes in Europe, Africa and Western Pacific. The radial geomagnetic field at the core–mantle boundary is investigated as the origin of the new jerk. Results show that the global-average secular acceleration of the radial field exhibits a new pulse at mid-2018, establishing the starting epoch of the 2020-jerk.

Reconstructing the Lancang Terrane (SW Yunnan) and implications for early Paleozoic Proto-Tethys evolution at the northern margin of Gondwana

The Lancang Group in SW Yunnan constitutes a pivotal component of the continental margin bounding the Proto- and Paleo-Tethys oceans, yet its formation timing, composition and tectonic affinity remain ill-defined. In this contribution, we present new zircon U-Pb age and whole-rock geochemistry data from volcanic and sedimentary rock units, which are compiled with published data, to refine the depositional age, provenance and nature of the group and its host terrane. The Lancang Group consists of five formations, two of which (Manlai and Huimin) contain abundant metavolcanic rocks. The metavolcanic rocks show a secular change in geochemistry, from EMORB-like calc-alkaline series of the ca. 495 Ma Manlai Formation, to arc-like high-K series of the Huimin Formation. Five metavolcanic samples from the Huimin Formation yielded zircon U-Pb ages between 478 ± 5 Ma and 442 ± 5 Ma. The late Cambrian-Ordovician arc magmatism is related to an active continental margin setting associated with subduction of the Proto-Tethys Ocean. The time-integrated geochemical variation shown by the volcanic rocks likely reflects evolving maturity of the arc system. The youngest detrital zircon ages of the five formations, in conjunction with age constraints from the interbedded volcanic rocks, suggest that the Lancang Group was largely accumulated during the early Paleozoic. The Lancang Terrane is reconstructed as a continental block, which formed part of the magmatically-active margin of the Proto-Tethys during the early Paleozoic. Provenance analysis based on detrital zircon age spectra and Hf isotope data indicates Gondwana affinities of the terrane. Furthermore, xenocrystic zircon ages and zircon Hf and whole-rock Nd model ages from igneous rocks support presence of Neoarchean-Mesoproterozoic basement underlying the terrane. The reconstructed Lancang Terrane bears important implications for understanding the configuration of the northern margin of Eastern Gondwana and the relationship between the Proto- and Paleo-Tethys oceans.

The Capitanian Minimum: A Unique Sr Isotope Beacon of the Latest Paleozoic Seawater

The long-term trend in the Paleozoic seawater 87Sr/86Sr was punctuated by a unique episode called the “Capitanian minimum” at the end of the Guadalupian (Permian; ca. 260 Ma). This article reviews the nature and timing of this major turning point in seawater Sr isotope composition (87Sr/86Sr, δ88Sr) immediately before the Paleozoic-Mesozoic boundary (ca. 252 Ma). The lowest value of seawater 87Sr/86Sr (0.7068) in the Capitanian and the subsequent rapid increase at an unusually high rate likely originated from a significant change in continental flux with highly radiogenic Sr. The assembly of the supercontinent Pangea and its subsequent mantle plume-induced breakup were responsible for the overall secular change throughout the Phanerozoic; nonetheless, short-term fluctuations were superimposed by global climate changes. Regarding the unidirectional decrease in Sr isotope values during the early-middle Permian and the Capitanian minimum, the suppression of continental flux was driven by the assembly of Pangea and by climate change with glaciation. In contrast, the extremely rapid increase in Sr isotope values during the Lopingian-early Triassic was induced by global warming. The unique trend change in seawater Sr isotope signatures across the Guadalupian-Lopingian Boundary (GLB) needs to be explained in relation to the unusual climate change associated with a major extinction around the GLB.

Long-term multiband monitoring of blazar 3C 66A: Evidence of the two distinct states with different baseline flux

ABSTRACT Blazar variability can be described as flaring activities on a wide range of time-scales over a baseline flux level. It is important to detect and distinguish baseline flux changes from long-term flare variations, since the former may reflect state transitions caused by a secular change in bulk properties such as the bulk Lorentz factor or the viewing angle. We report such a transition observed in the 11 yr Fermi γ-ray light curve of the blazar 3C 66A, where the baseline flux of ∼1.8 × 10−7 ph cm−2 s−1 persisted for three years and then changed over a month time-scale to ∼0.8 × 10−7 ph cm−2 s−1 and remained in that level for the next eight years. Moreover, there is evidence for a similar shift in baseline flux in the optical band. Broad-band spectral energy distribution modelling for the two activity states reveals that the baseline flux change is consistent with an overall decrease in the Doppler factor, which in turn implies an increase in the jet inclination angle by ∼1° or a decrease in the bulk Lorentz factor by ∼25 per cent. We discuss the implication of such a variation occurring on a month time-scale.