家蚕繭調査におけるサンプリングの方法

(1) 繭重平均値の推定方法

抄録

In this paper, I report sampling experiments for estimating the population mean value of silkworm cocoon (Bombyx mori).
The materials were obtained from cocoons of Shi 122×Nichi 122 (1000 individuals for each sex). Measurements were carried out using a balance which was properly prepared for weighting cocoons, the scale being read by every 1cg.
The results obtained are as follows:
1. The frequency distributions of the cocoon weights are shown in Table 1. It is shown in Table 2 that the distribution types of the cocoon weights in the population are not the normal ones.
2. The distribution-types of the sample mean value are shown to be normal ones in Table 4. and Table 5.
3. Various formulae deduced from the normal distribution can be safely applied to the cocoon weight values through the central limit theorem, for example the calculated values are almost equal to the observed ones with regard to the standard deviation of the sample mean values.
4. The size of the sample (the number of cocoons) can be computed using the formula (4), where σ represents the standard deviation of the population distribution; σ_x, the standard deviation of the sample mean value distribution; N, the number of cocoons contained in the population; n, the number of cocoons contained in the sample. The values of K are 2.58 and 1.96 in the cases of confidence-coefficients being 99% and 95% respectively. It seems adequate to determine the value of b as 2.5cg. for σ cocoon weight.