Jw Odhiambo

Ages of eruption of the permanent teeth in Kenyan African and Asian children

Mean ages of eruption of the permanent teeth (except 3rd molars) in African and Asian children were derived from a cross-sectional study of 2847 children aged 4-14 years, in selected nursery and primary schools in Nairobi, Kenya. Except for the premolars, the mandibular teeth erupted earlier than the maxillary ones in both races. The mandibular incisors and canines erupted earlier by 0.9-1.1 yr in Africans and 0.6-0.8 yr in Asians, and the molar by 0.2-0.4 yr in both races. The maxillary premolars were ahead of mandibular premolars by 0.1-0.2 yr in both races. The females were ahead of males in both races. Compared with the Asians, the African permanent teeth erupted earlier by 0.2-0.7 yr. The most frequent order of eruption in Africans is Mand I1, Mand M1, Max M1, Mand I2, and Max I1 between 5-7 years, while in the Asians the most frequent order is Mand M1, Mand I1, or Max M1, Max I1 and Mand I2 between 6-8 years. The incidence of Cusp of Carabelli in Africans and Asians is about 19-25%.

Estimation of calendar age from eruption times of permanent teeth in Kenyan Africans and Asians

Eruption data for permanent teeth, obtained from a previous cross-sectional study of 2847 African and Asian school children aged 4-14 years in Nairobi, Kenya, were used to calculate the median age and the 10th-90th percentile range of age, for a given number of teeth present. For a limited period (5-13 years) up to the time of eruption of second molars, the total number of permanent teeth erupted can be used to estimate the age of a child, with an error which increases with the number of teeth present. The range of this error is about 18-30% of the median age for African males, 21-29% for African females, 15-33% for Asian males and 18-33% for Asian females, with a 1 in 5 chance that the error may exceed these limits.

On multistage group screening designs

In this article we discuss multistage group screening in which group-factors contain differing number of factors. We describe a procedure for grouping the factors in the absence of concrete prior information, so that the relative testing cost is minimal. It Is shown that under quite general conditions, these designs will require fewer runs than the equivalent designs in which the group-factors contain same number of factors.

Step-wise group screening designs with errors in observations

The performance of step-wise group screening In terms of the expected number of runs and the expected number of incorrect decisions, Is considered. A method for obtaining optimal step-wise designs Is presented, for the cases in which the direction of each defective factor is assumed to be known a-priori and the observations are subject to error.

A transition model for estimating academic survival through cohort analysis

To evolve an efficient system, educational activities need to be carefully coordinated, for which an abstract realization of the real system is essential. A transition model is one which describes the stocks and flows of students through an education system in terms of transition ratios. In this paper we describe one such model, which traces the flow of a cohort of students through the system. We note some consequences of the model and give some results of its application in Kenya.

Three-stage group screening with unequal group sizes and with errors in observations

In this paper three-stage group screening in which group-factors contain differing number of factors is discussed. A procedure for grouping the factors in the absence of concrete prior information is described. Formulas for the expected number of runs and the expected number of incorrect decisions have also been obtained. These formulas are used to formulate criteria for optimal designs.

The performance of multistage group screening designs

This article deals with multistage group screening in which group-factors contain the same number of factors. A usual assumption of this procedure is that the directions of possible effects are known. In practice, however, this assumption i s often unreasonable. This paper examines, in the case of no errors in observations, the performance of multistage group screening when this assumption is false . This enails consideration of cancellation effects within group-factors.

On improved estimation under additional information

An improvement of the ordinary least squares estimator of the regression vector in a univariate linear model is obtained. This is done by combining observed data with prior information and other additional information. Important features include admissibility in the unrestricted and restricted cases.

On the performance of three-stage group screening experiments

This paper examines the performance of three-stage group screening in terms of the mean number of tests needed; and the proportion of active factors correctly detected by the screening plan, A linear cost function is also proposed, To evaluate performance, random grouping and a constant signa1-to -noise ratio for all active factors, are assumed.