المؤلف
الملخص
The paper included approximate methods that give approximate solution. There solutions give approximate formulas for the mean variance of stratified sampling .
The first method for finding optimal stratum boundaries is .proposed by dalenus, then it was studied and adopted by many scholars such as serfling 1968.He proposed and found that. He optimal variance for this method is .
In 1976 Thomsen proposed another method namely where He supposed to find the optimal variance.
In 1993 AL-Kasab proposed another method namely; .
In 1995 AL_Daghistani proposed a new method namely; .
In this research we suggest a new approximation named the; method of proportional allocation .we assumed ,and found that the optimal variance for this method is .
A comparison of this method with the above mentioned is given depending on three theoretical distributions: Uniform, Normal, and exponential distributions. This comparison is made by calculating the variance.
Method showed some variances in results. It has been found that this method is the most efficient from other method in uniform distribution case. Table (3-1). The larger the value of (σ),the more efficient the method would be in the normal distribution .the smaller the value of (λ),the more efficient the method world be in the exponential distribution as can be seen from tables ( 3-2 ), ( 3-3).
الكلمات الرئيسة
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