L’annualisation des chiffres d’exercices financiers

Une façon répandue de transformer des chiffres d’exercices financiers en estimations d’année civile consiste à considérer l’estimation civile comme une fraction (par exemple 1/4) d’un chiffre financier et d’une fraction complémentaire (3/4) du chiffre financier suivant. À titre d’exemple, si l’année financière se termine en mars, l’estimation de 1987, disons, est l’addition des deux chiffres suivants : 1/4 du chiffre de 1986-87 et 3/4 du chiffre de 1987-88. Selon le présent article, ce procédé est acceptable seulement si les chiffres financiers sont en hausse (ou en baisse) ininterrompue. En effet, en cas de changement de direction  — et même de plafonnement  — des chiffres financiers, le procédé implique un comportement invraisemblable de la composante conjoncturelle sous-jacente. Ceci complique l’analyse conjoncturelle, la prise de décision et la gestion macro-économique. L’article compare le procédé à une méthode récemment mise au point par Cholette et Baldwin (1989). Cette dernière est essentiellement une adaptation des méthodes utilisées pour l’étalonnage, c’est-à-dire pour l’ajustement de séries infra-annuelles à des jalons annuels (Denton, 1971; Bournay et Laroque, 1979); de même qu’une adaptation des méthodes utilisées pour l’interpolation entre valeurs annuelles civiles (Boot, Feibes et Lisman, 1967).A very common procedure to convert fiscal year data into calendar year values consists of setting the calendar year estimate equal to a fraction (e.g. 1/4) of one fiscal year value plus a complementary fraction (e.g. 3/4) of the next fiscal value. For instance if the fiscal year ends in March, the 1987 estimate (say) is equal to 1/4 of the 1986-87 fiscal value plus 3/4 of the 1987-88 value. According to this paper, this procedure is satisfactory only for fiscal data which display uninterrupted growth. Indeed if the fiscal data change direction or even level-off, the procedure implies a very unlikely behaviour of the underlying trend-cycle component. This in turn complicates business cycle analysis, decision making and macro-economic management. The paper compares the procedure to a method recently developed by Cholette and Baldwin (1989). The method is essentially an adaptation of the methods used for benchmarking, that is for adjusting sub-annual series to yearly benchmarks (Denton, 1971; Bournay and Laroque, 1979); and an adaption of the methods used for interpolating between calendar year values (Boot, Feibes and Lisman, 1967)

La désaisonnalisation pour le non-spécialiste

This paper provides simple descriptions and interpretations of the components found in time series: the trend, the cycle, the seasonal, the trading-day and the irregular components. Furthermore, the necessity and the justification ofseasonal adjustment are explained. It is however reminded the seasonally adjusted series should not be used for model building

La prévision à l’aide des modèles ARMMI et d’information à priori

The method of ARIMA forecasting with benchmarks developed in this paper allows the production of univariate forecasts which take into account the historical information of a series, captured by an ARIMA model (Box and Jenkins, 1970), as well as partial prior information on the future behaviour of the series. The prior information, or benchmarks, stems from the conclusions of a study on the phenomenon to be extrapolated, from forecasts of an annual econometric model or simply from pessimistic, realistic or optimistic scenarios contemplated by the current economic analyst. It may take the form of annual levels to be achieved, of neighbourhoods to be reached for a given time period, of movements to be displayed or more generally of any linear criteria to be satisfied by the forecasted values. By means of this method, the forecaster may then exercize his current economic evaluation and judgement to the fullest extent in deriving the forecasts, since the labouriousness and the "trial and errors" experienced without a systematic method are avoided

Analyse spectrale des filtres de la méthode de désaisonnalisation X-11-ARMMI

This paper examines the changes produced on the seasonal estimates of the X-11-ARIMA method (Dagum, 1980), when (1) the two by twelve preliminary trend-cycle estimator is replaced by that of Cholette (1979a) (now optional in the program) and when (2) the "end" weights of the seasonal three by three and three by five moving averages are modified.The results show that the first substitution has a small but desirable effect which becomes more substantial for short series and for those with fast cyclical movements. On the other hand, the suggested replacement of the seasonal end weights would entail considerable improvements for series with stable seasonality or with much irregularity. Both modifications do not affect the properties of X-11-ARIMA in the "centre" of long series

La prévision à l’aide des modèles ARMMI et d’information à priori

The method of ARIMA forecasting with benchmarks developed in this paper allows the production of univariate forecasts which take into account the historical information of a series, captured by an ARIMA model (Box and Jenkins, 1970), as well as partial prior information on the future behaviour of the series. The prior information, or benchmarks, stems from the conclusions of a study on the phenomenon to be extrapolated, from forecasts of an annual econometric model or simply from pessimistic, realistic or optimistic scenarios contemplated by the current economic analyst. It may take the form of annual levels to be achieved, of neighbourhoods to be reached for a given time period, of movements to be displayed or more generally of any linear criteria to be satisfied by the forecasted values. By means of this method, the forecaster may then exercize his current economic evaluation and judgement to the fullest extent in deriving the forecasts, since the labouriousness and the "trial and errors" experienced without a systematic method are avoided.

Analyse spectrale des filtres de la méthode de désaisonnalisation X-11-ARMMI

This paper examines the changes produced on the seasonal estimates of the X-11-ARIMA method (Dagum, 1980), when (1) the two by twelve preliminary trend-cycle estimator is replaced by that of Cholette (1979a) (now optional in the program) and when (2) the "end" weights of the seasonal three by three and three by five moving averages are modified.

Heliostat-field soiling predictions and cleaning resource optimization for solar tower plants

This paper presents a novel methodology for characterizing soiling losses through experimental measurements. Soiling predictions were obtained by calibrating a soiling model based on field measurements from a 50 MW modular solar tower project in Mount Isa, Australia. The study found that the mean predicted soiling rate for horizontally fixed mirrors was 0.12 percentage points per day (pp/d) during low dust seasons and 0.22 pp/d during high seasons. Autoregressive time series models were employed to extend two years of onsite meteorological measurements to a 10-year period, enabling the prediction of heliostat-field soiling rates. A fixed-frequency cleaning heuristic was applied to optimise the cleaning resources for various operational policies by balancing direct cleaning resource costs against the expected lost production, which was computed by averaging multiple simulated soiling loss trajectories. Analysis of resource usage showed that the cost of fuel and operator salaries contributed 42 % and 35 % respectively towards the cleaning cost. In addition, stowing heliostats in the horizontal position at night increased daily soiling rates by 114 % and the total cleaning costs by 51 % relative to vertically stowed heliostat-field. Under a simplified night-time-only power production configuration, the oversized solar field effectively charged the thermal storage during the day, despite reduced mirror reflectance due to soiling. These findings suggest that the plant can maintain efficient operation even with a reduced cleaning rate. Finally, it was observed that performing cleaning operations during the day led to a 7 % increase in the total cleaning cost compared to a night-time cleaning policy. This was primarily attributed to the need to park operational heliostats for cleaning

A Dual-Mode Model Predictive Control Algorithm Trajectory Tracking in Discrete-Time Nonlinear Dynamic Systems

In this paper, a dual-mode model predictive/linear control method is presented, which extends the concept of dual-mode model predictive control (MPC) to trajectory tracking control of nonlinear dynamic systems described by discrete-time state-space models. The dual-mode controller comprises of a time-varying linear control law, implemented when the states lie within a sufficiently small neighborhood of the reference trajectory, and a model predictive control strategy driving the system toward that neighborhood. The boundary of this neighborhood is characterized so as to ensure stability of the closed-loop system and terminate the optimization procedure in a finite number of iterations, without jeopardizing the stability of the closed-loop system. The developed controller is applied to the central air handling unit (AHU) of a two-zone variable air volume (VAV) heating, ventilation, and air conditioning (HVAC) system

Elucidating Drivers for Variations in the Explosive Human Immunodeficiency Virus Epidemic among People Who Inject Drugs in Pakistan

BACKGROUND: Pakistan’s explosive human immunodeficiency virus (HIV) epidemic among people who inject drugs (PWID) varies widely across cities. We evaluated possible drivers for these variations. METHODS: Multivariable regression analyses were undertaken using data from 5 national surveys among PWID (n = 18 467; 2005–2017) to determine risk factors associated with variations in city-level HIV prevalence. A dynamic HIV model was used to estimate the population-attributable fraction (PAF; proportion of HIV infections prevented over 10 years when that risk factor is removed) of these risk factors to HIV transmission and impact on HIV incidence of reducing their prevalence. RESULTS: Regression analyses suggested that city-level HIV prevalence is strongly associated with the prevalence of using professional injectors at last injection, heroin use in last month, and injecting ≥4 times per day. Through calibrating a model to these associations, we estimate that the 10-year PAFs of using professional injectors, heroin use, and frequent injecting are 45.3% (95% uncertainty interval [UI], 4.3%–79.7%), 45.9% (95% UI, 8.1%–78.4%), and 22.2% (95% UI, 2.0%–58.4%), respectively. Reducing to lowest city-level prevalences of using professional injectors (2.8%; median 89.9% reduction), heroin use (0.9%; median 91.2% reduction), and frequent injecting (0.1%; median 91.8% reduction) in 2020 reduces overall HIV incidence by 52.7% (95% UI, 6.1%–82.0%), 53.0% (95% UI, 11.3%–80.2%), and 28.1% (95% UI, 2.7%–66.6%), respectively, over 10 years. CONCLUSIONS: Interventions should focus on these risk factors to control Pakistan’s explosive HIV epidemic among PWID, including a concomitant expansion of high-coverage needle/syringe provision, opioid substitution therapy, and antiretroviral therapy

A cross-sectional survey exploring HIV and HCV prevalence among men who purchase sex in Dnipro, Ukraine

BACKGROUND: HIV programming in Ukraine largely targets "key population" groups. Men who purchase sex are not directly reached. The aim of our study was to explore the prevalence of sexually transmitted and blood-borne infections (STBBIs) among men who purchase sex from female sex workers. METHODS: Following geographic mapping and population size estimation at each "hotspot", we conducted a cross-sectional bio-behavioural survey with men who purchase sex between September 2017 and March 2018 in Dnipro, Ukraine. Eligibility criteria included purchasing sex services at a "hotspot" and being ≥ 18 years. Participants completed a structured questionnaire, followed by HIV/HCV rapid testing and a dried blood spot (DBS) sample collection for confirmatory serology. RESULTS: The study enrolled 370 participants. The median age was 32 (interquartile range [IQR] = 27-38) and the median age of first purchase of sexual services was 22 (IQR = 19-27). Over half (56%) of participants reported ever testing for HIV; four participants (2%, N = 206) reported having tested positive for HIV, with three out of the four reporting being on ART. Forty percent of participants had ever tested for HCV, with three (2%, N = 142) having ever tested positive for HCV. In DBS testing, nine participants (2.4%) tested positive for HIV and 24 (6.5%) tested positive for ever having an HCV infection. CONCLUSION: Prevalence of HIV and HCV in this population was high. Given high rates of study enrolment and testing, efforts should be made to reach men who purchase sex with expanded STBBI programming