Optimale betrouwbaarheid van parallelle meervoudige systemen

In this paper the reliability of parallel multi-component systems will be considered.
The number and kind of spare components wil be determined for maximum improvement in reliability under the assumption that limited funds are available for the purpose.     

De oplossing van een kwaliteitsprobleem door het gebruik van proefschema's

Samenvatting  Het artikel geeft een beschrijving van de strategie en de methoden, die worden gebruikt voor het zoeken naar de oorzaak van een kwaliteitsvermindering bij dubbelspiralen voor gloeilampen. Er wordt niet alleen aandacht besteed aan de beschrijving en motivering van de gekozen proefschema's maar ook aan de praktische uitvoering van de experimenten. Het fabricage-proces is nl. dermate gecompliceerd dat niet kon worden volstaan met de instructie de experimenten in aselecte volgorde uit te voeren.
Het gehele onderzoek wordt uitqevoerd aan de hand van een drietal proefschema's. De keuze van het tweede en derde proefschema volgt logisch uit de uitkomsten van de voorafgaande proef. Na vol-tooiing van de derde proef is ondubbelzinnig aangetoond dat de belangrijkste oorzaak van de kwaliteitsvermindering is gevonden.     

De bewerking van veldproeven volgens de methode van Knut Vik

Summary  (The treatment of field experiments by Knut Vik's method).
Agriculturists and statisticians have studied the problem, how to free the yields in a field experiment from the inequality of the soil. The method of the analysis of variance, due to the English statistician R. A. Fisher has taken an important place in the study of field experiments, so that other methods fell in the background.
The Norwegian agriculturist Knut Vik has suggested a method, which leads to good results without complicated calculations and without the knowledge of a great part of the mathematical statistics.
The mathematical foundation of this method is discussed in this article, which concludes, that the method of Knut Vik is of great importance for agriculturists, who don't want to perform intricate calculations.     

De spreiding van inschrijvingsbedragen op openbare aanbestedingen

Summary
The Dispersion of Bids in Public Contracting
The analysis is concerned with the coefficients of variation (standard deviation divided by mean) of bids in public contracting by the municipal authorities of a big city in the period 1946–1953. Three factors are investigated as to their impact on these coefficients of variation. The first is time; it is shown that the dispersion decreased gradually, probably as a result of increased cartelization. The second is the nature of the object (road building and earth-work, waterworks, and sewerage); waterworks seem to be characterized by a smaller dispersion of bids. The third is the size of the object, and it is shown that the dispersion is smaller for large objects than for small ones, probably as a result of the greater care of cost calculation for large objects. An attempt is also made to ascertain the interaction of these factors.     

De statistiek van de Militair Geneeskundige Dienst

The author gives a review of the origin and use of the statistical material used in the medical corps of the Dutch army. He points out the value of employing the data in a statistical manner for planning the medical care of the troops.     

De invloed van de keuze der gewichten op de hoogte van een gewogen indexcijfer

The influence of the choice of the weights on the value of an indexnumber.
Price and quantity indexnumbers are weighted averages of groups of price and quantity ratios and they are convenient instruments to indicate the general tendency of such groups, especially if the number of basic ratios is considerable. The frequent use of indexnumbers is due to the fact that they can often be applied to problems for which, strictly speaking, an indexnumber had to be used derived from the same group of ratios but based on a different set of weights.
Two typical examples of such problems are given.
The use of a set of weights differing from the appropriate one is only justified, however, when the indexnumber is rather insensitive to changes in the set of weights. A simple formula is derived showing that the relative change of an index-number due to a change in the set of weights is equal to the product of the (weighted) coefficient of variation of the basic ratios, the (weighted) standard deviation of the relative changes of the weights and the (weighted) coefficient of correlation of the ratios and of the relative changes. The system of weights used in the calculation of these three factors is the same and is equal to the set of true weights belonging to the problem under consideration.
The practical use of the formula is demonstrated at the problem of index-numbers of costs frequently encountered in the practice of cost accounting.     

De fout bij het gebruik van een tweetal benaderingsformules

Summary For the sake of efficiency, the use of simplified formulae in item analysis is recommended. For adequate use of such formulae the systematic error must be known. For two important formulae this error is estimated: the KUDER-RICHARD-SON-21 (instead of 20) and a formula for the correction of the spurious part-whole correlation. As for the KR, if itemscores are 1 andO, the KR20 is given in (I) and the KR21 in (2). The difference dr between them, given in (5), is directly proportional to the variance of the itemdifficulties. This variance turns out to be rarely greater than 0,05. If the distribution of itemdifficulties is unimodal, a value greater than 0,05 is indeed improbable in four-choice tests. The KR21, which does not need an item analysis, can be used as a substitute of the KR20. The KR21 coefficient itself is an lower limit, the KR21 plus dr - estimated by (6) - a probable upper limit of the KR20 coefficient. The part-whole correlation of tests is spurious. If one wants to correct for this spuriousness it is theoretically preferable to estimate the part-parallel test correlation instead ofthe part rest correlation. This is done here with the assumptions of classical test theory. The part-parallel test correlation is given in (12), the easily computed first approximation, called A, in (13) and the second approximation in (75), in which last formula the corrected correlation is expressed as a function of A, the standard deviations of part and whole, and the reliability of the test. One can compute with this formula a maximum A, below which the first approximation is sufficiently precise.     

De Computer: Werkwijze en toepassingsmogelijkheden van elektronische rekenmachines

Since world-war II, there has been an enormous development in the field of the electronic data processing equipment.
This rapid development was on one side due to the boom which followed the war, on the other hand the armaments-race contributed considerably to a further increase of the research in this sector.
In the years 1948–50 it became clear that this equipment could also be of great advantage in other areas than scientific, such as business administration, automatic translation, information retrieval and production control. These applications, however, made other demands on the computer. A greater and faster memory and more speed in input and output of data were necessary. The research in the last few years is therefore mainly concentrated on these problems.
The computers, as they are now available, consist of 5 units: input device, calculating-unit, storage, control unit and output device. The processing is controlled by means of a program, which consists of a number of instructions, prescribing in detail the operations to be performed by the machine.
It will be clear that the use of this equipment requires a careful study beforehand, whilst also the implications on staff and organisation must be considered.     

De theoretische zijde van de methode der kleinste kwadraten

The theoretical aspect of least squares.
This article contains a slightly modified presentation of the Markoff theory of least squares as developed along different lines by Aitken and by David and Neyman. The modifications aim at a more complete treatment and a geometrical illustration of the connection between best linear estimates and generalized least squares. The unbiasedness of ordinary least squares estimates in the case of heteroscedastic and correlated errors is stressed and the loss of efficiency is shown to be generally small. Topics like orthogonalization, partial correlation and what is called "over-correlation" are treated in passing.
Matrices are constantly used, being the adequate tools in this matter. In the appendix a special relevant matrix theorem is derived, viz. a generalization of the well known Cauchy inequality.     

De gemiddelde bezetting van personenauto's in interlokaal verkeer*

Summary This paper, read in Utrecht on October 14th 1965, deals with the average occupancy of cars outside urban areas. During the years 1962 and 1963 more than 500 samples (each consisting of 150 cars) have been taken on two points of the dutch road-system. The samples covered the different months, days (sundays, Saturdays and week-days) and hours (except those without daylight). The average occupancy turned out to be 1.8 on week-days (with a minimum of 1.4), 2.5 on Saturdays (with a minimum of 2.1) and 3.1 on Sundays (the over-all average for all days being 2.1). These results seem to be representative for the whole dutch car traffic as is shown by comparison with observations on other points and other data. Comparison of the seasonal, weekly and hourly patterns of the average occupancy with those of the car traffic density enable to draw conclusions about the responsibility of different kinds of traffic (commercial and commuter traffic versus social traffic) for congestion and for the construction and maintenance cost of the road-system.     

De frequentistische opbouw van de waarschijnlijkheids-rekening volgens R. von Mises

R. von M ises publiceerde zijn frequentistische opbouw van de waarschijnlijkheidsleer voor het eerst in 1919. De daarbij naar voren gebrachte inzichten verschilden zeer van de in die tijd algemeen geaccepteerde ideeén omtrent de grondslagen van de waarschijnlijkheidsleer. Onder invloed van (zowel opbouwende als abrekende) kritieken, alsmede door eigen gewijzigde inzichten, evolueerde zijn theorie zich, via diverse publikaties, tot die, weke wij aantreffen in zijn in 1964 posthuum verschenen, laatste werk.
In dit artikel wordt nader ingegaan op de theorie van V on M ises , zoals die in het zojuist genoemde werk behandeld wordt. Hiertoe is het soms nodig in te gaan op vroegere publikaties van zijn hand.
In vele boeken en artikelen (zie bijv. C ramer (1966) p. 150 en H emelrijk (1968) p. 13) worden enige zinnen gewijd aan het feit, dat V on M ises zich met de grondslagen van de waarschijnlijkheidsleer heeft bezig gehouden. Bijna nooit krijgt men echter te lezen, wat hij precies gezegd heeft.