Uncertainty in measurement and control

Summary Controlling is intervening in a situation on the basis of measurements. The three elements occurring in this definition may each contain an uncertainty that sets a limit to the control efficiency: The measurements may be in error owing to both inaccuracies and sluggishness of the measurements. Proper and rapid data-processing is essential therefore. The interventions may lose part of their effect through over-determinancy or dynamically unfavourable (sluggish) responses. In either case statistical calculations disclose the average control errors that are liable to be made, and also the way in which these can be minimized. The situation may be unclear, i.e. the static and dynamic process characteristics are insufficiently known. In such cases regression and correlation techniques may aid in finding a solution. Following a general review, we shall discuss in more detail those aspects that are bound up with the dynamics of the phenomena. Arguments from information theory reveal that the dynamic efficiency of control actions depends on correlation functions of time series (disturbances) and response curves of the systems (processes). The effects of disturbance correlation time, disturbance variance, sampling time, sample treatment, measuring errors, measuring time, rapidity of the intervention, etc., on the efficiency are elucidated by means of some formulae, graphs and examples.     

De betrouwbaarheid van controleurs

Summary  (The reliability of 100% inspection).
The article of Mr, Enters on The reliability of 100% inspection in the first issue of Statistica is critizised.
The criterion of goodness of control as the sum of the coefficients of correlation between the measurements of the individual inspectors and each of their colleagues does not agree with the everyday use of that criterion, i.e. the correlation between the observed' and the real diameters etc. Nor is this criterion identical with the Spearman criterion of saturation coefficients.
Some suggestions are given for solution of the problem, e.g. psychotechnical testing the inspectors, analysis of the frequency curves of their measurements and computation of the coefficients of correlation between the measurements of each inspector and the corresponding average measurements of all inspectors.     

Over toleranties on passingen in den machinebouw

Tolerance problems in mechanical engineering ought to be treated with statistical methods.
It is shown that the use of range (instead of standard deviation) for measuring variability in tolerances and fits leads to systematic errors.
The suggestion is made to measure variability in mechanical engineering by T = 4,65 , being the 98%-range in the case of normal distribution.
A simple statistical approach to selective assembling is mentioned.     

The New View on Editing

Numerous evaluation and other studies show that the heavy cost of editing cannot be justified by quality improvement. It is necessary to replace the old paradigm-the more and tighter the checks and recontacts, the better the quality-by a new-focus the editing on identifying and collecting data on errors, problem areas, and error causes to provide a basis for a continuous improvement of the whole survey vehicle.
The corner stone of the new view on editing is that the entire set of the query edits should be designed meticulously, be focused on errors influencing the estimates, and be targeted on existing error types which can be identified by edits, and finally that the effects of the edits should be continuously evaluated by analysis of performance measures and other diagnostics, which the process should be designed to produce.
The paper is a short introduction to modern editing under the new view. It presents, also, some facts to the low efficiency of traditional editing, and explains it by giving a historical review of editing.     

Additive hazards regression of failure time data with covariate measurement errors

This paper discusses regression analysis of failure time data under the additive hazards model, with covariates subject to measurement errors. In particular, we consider the situation where there may exist only repeated measurements or observations on the covariates with measurement errors, and for which there does not exist any method for inference. A nonparametric-correction approach is proposed for inference about regression parameters and the baseline cumulative hazards function. Both asymptotic and finite sample properties of the proposed estimators are established and the approach is applied to an AIDS clinical trial that motivated this study.     

Econometric Models and Economic Forecasting

This Briefing Paper is thejirst ofa series of three designeddiscussed is the process of making 'constant adjustments' in forecasts. This process involves modifying the results generated by the econometric model. For the first time we are publishing tables of the constant adjustments used in the current forecast. We explain in general why such adjustments are made and also explain the actual adjustments we have made for this forecast.
The second article of the series, to be published in our February 1983 edition, will describe the potential sources of error in forecasts. In particular it will describe the inevitable stochastic or random element involved in e tatistical attempts to quantify economic behaviour. As a completely new departure the article will report estimates of future errors based on stochastic simulations of the LBS. model and will provide statistical error bad for the main elements of the forecast.
The final article, to be published in our June 1983 edition, will contrast the measures of forecast error that e e obtain from the estimation process and our stochastic e imulationsp with the errors that we have actually made, as revealed by an examination of our forecasting 'track record'. It is hoped to draw, from this comparison, some e eneral conclusions about the scope and limits of econometric forecasting producers.     

Een noodzakelijke correctie van de overschrijdingsgrenzen voor steekproefgemiddelden bij toepassing van stratified sampling

Summary  (A necessary correction of the control chart limits for averages of samples in the case of stratified sampling).
Application of stratified sampling results in smaller fluctuations of sampling than where the same total number of individuals is drawn at random from the superposed strata.
The proportion of the standard errors of the averages obtained by these two sampling methods may be expressed by a factor φ (o ≤φ≤ 1). The probability limits, between which the random sampling results would be fluctuating normally, should be corrected according to this factor.
A few properties of φ are discussed. This is graphically illustrated. Remarks have been added about the relation between the shape of the population of the sampling averages and the population from which the individuals are drawn, and about the difficulties which arise when the populations are non-Gaussian.     

航天测量船经纬仪系统误差动态修正方法

星体标校技术是利用恒星在天球上的准确视位置标定光电经纬仪误差的一种方法。文章通过对星体标校基本原理分析,推导出适用于航天测量船经纬仪系统误差动态标定公式,并提出动态条件下误差修正的新方法。应用结果表明:该方法具有一定的实际应用价值,能够解决动态情况下经纬仪系统误差修正的技术难题,极大提高经纬仪测量精度,投资小、精度高,具有较高的可信度。     

Het voorspellen van levertijden uit gegevens over de voort-gang van een project

Estimation of dates of delivery by extrapolation of progress-data for a project.
The problem can be put in mathematical form with the aid of some assumptions with regard to the occurrence of interruptions.
The progress of the project is supposed to be interrupted by time-intervals during which progress is fully stopped. These intervals start at irregularly distributed moments and have a variable size. The points on the time axis corresponding with the moments of stagnation will show a constant average density, if a constant average production capacity or development capacity is available. This means that the results are valid only if no alterations are made which influence the general progress of the project involved.
The application of probability theory to problems connected with promises of delivery may, in general, look unacceptable.
Many projects, however, have an experimental character and unforeseen technical and organisational troubles are unavoidable.
In such cases the theory makes it possible to obtain a maximum amount of information contained in the progress-data and may help management to make the best decisions.     

Heteroskedasticity, autocorrelation, and spatial correlation robust inference in linear panel models with fixed-effects

This paper develops an asymptotic theory for test statistics in linear panel models that are robust to heteroskedasticity, autocorrelation and/or spatial correlation. Two classes of standard errors are analyzed. Both are based on nonparametric heteroskedasticity autocorrelation (HAC) covariance matrix estimators. The first class is based on averages of HAC estimators across individuals in the cross-section, i.e. “averages of HACs”. This class includes the well known cluster standard errors analyzed by Arellano (1987) as a special case. The second class is based on the HAC of cross-section averages and was proposed by Driscoll and Kraay (1998). The ”HAC of averages” standard errors are robust to heteroskedasticity, serial correlation and spatial correlation but weak dependence in the time dimension is required. The “averages of HACs” standard errors are robust to heteroskedasticity and serial correlation including the nonstationary case but they are not valid in the presence of spatial correlation. The main contribution of the paper is to develop a fixed-b asymptotic theory for statistics based on both classes of standard errors in models with individual and possibly time fixed-effects dummy variables. The asymptotics is carried out for large time sample sizes for both fixed and large cross-section sample sizes. Extensive simulations show that the fixed-b approximation is usually much better than the traditional normal or chi-square approximation especially for the Driscoll-Kraay standard errors. The use of fixed-b critical values will lead to more reliable inference in practice especially for tests of joint hypotheses.     

Frontier Production Functions and Technical Efficiency Measures

The concept of technical efficiency is central to measuring the firm performance. The measurement of technical efficiency has proved difficult and complex, and the literature provides a range of methodologies. This paper reviews the various methodologies for measuring technical efficiency and offers a comparison between established methods of measurements. The discussion is literary with less mathematical jargons and equations. The objective of this paper is not to be exhaustive, but to be up‐to‐date and to provide a significant discussion on some of the core methods of measuring technical efficiency.     

Produktiviteitsverhoging op grote schaal: Maatnormalisatie van kleding

The article contains a short review of a campaign, undertaken in Holland during the last 12 years to arrive at standardized sizes for women's and men's clothing. The first campaign was undertaken by a department store, the second one by the clothing industry.
The operational value of a sizing system depends on the value of three parameters which are not, of course, independent of each other: coverage of the system, number of sizes and average cost of alterations.
The basis of the standardization is furnished by measuring a sample of the population of customers and by measuring the fitting-tolerances of clothing.
The proposed sizing systems are:
a. Ladies' dresses — a two-dimensional system based on waist girth and length of back, containing 14 sizes and giving a coverage of 90%.
b. Men's suits — a system with a variable number of dimensions (2 to 4). The identification dimensions are waist girth, length of leg, hip girth and inclination of shoulder. The proposed system gives a coverage of 90% with 34 sizes. Both systems have been experimentally verified.
Stress is laid on the necessity of an international sizing standardization.     

Een systeem van kostenbeheersende productieplanning

In this paper a system of cost-controlled production planning is described. This system considers all kinds of costs associated with a production in phases (e.g. production of units, production of subassemblies, assembly) which may be affected by the planning, such as set-up costs, costs of transport, control, inventories, capacity and changes in capacity.
The mathematical model leads to a linear or mixed discrete-linear programming problem whose solution gives for each time period considered the size of the capacities which should be used and of the series of different products which should be produced. Practical recommendations are given for obtaining a sufficiently satisfying solution.     

Eenige statistische opmerkingen over verpakkingsen doseeringsproblemen

In packing powders, fluids and the like in mass production there are three frequency distributions of weights, viz. net weights, gross weights and tare weights. It is shown that by elementary statistical methods the standard deviation of one of these three distributions may be found by analysing the other two.
The excisting correlation, e.g. between net weights and tare weights, can be found by the same methods.     

STATISTICA: De Overschrijdingskans

If we want to check a hypothesis by numbers, obtained from measuring or from counting in a random sample, practically always a difference will be found between these numbers and those, derived from that hypothesis-Such a difference may be caused by faults in the hypothesis or by factors which we do not want to analyse such as faults in the measuring or the influence of the sampling or influences acting together with the one regarded in our hypothesis.
The theory of statistics shows a way to estimate the chance that such another cause would result into a difference equal to or large than the one actually found. If in a given case this "chance of surpassing" is found to be small, we have to reject the hypothesis concerned. The smaller this chance is the larger is the likelihood of that rejection; it is the estimate of the likelihood of each statistical conclusion.     

FORMASY FOrecasting and Recruitment in MAnpower Systems

In this paper the tools are developed for forecasting and recruitment planning in a graded manpower system. Basic features of the presented approach are:
- the system contains several grades or job categories in which the employees stay for a certain time before being promoted or leaving the system,
- promotability and leaving rate for any employee depend on time spent in the job category and personal qualifications (like education, experience, age),
- recruitment is not necessarily restricted to the lowest level in the system,
- several planning aims and restrictions are allowed.
The approach is based on a generalized Markov model for the dynamic behaviour of an individual employee. A forecasting procedure and a recruitment-scheduling procedure are based on this Markov model.