(a)_(m)+(b)_(1)+(b)_(2)+... +(b)_(n)}(m+n)=-|||-dfrac (m)(m+n)cdot dfrac ({a)_(1)+(a)_(2)+... +(a)_(m)}(m)+dfrac (n)(m+n)cdot dfrac ({b)_(1)+(b)_(2)+... +(b)_(n)}(n)-|||-于是,当已知上述两层构成的样本中每层的-|||-平均数分别为x1和x2时,可得这个新样本-|||-的平均数为 dfrac (m)(m+n)(x)_(1)+dfrac (n)(m+n)(overline {x)}_(2) --|||-记 (omega )_(1)=dfrac (m)(m+n) (omega )_(2)=dfrac (n)(m+n) ,则这个新样本的-|||-平均数为 __ ,其中w1,w2称-|||-为权重.-|||-更一般地,设样本中不同层的平均数和相应-|||-权重分别为x1,x2,···,xn和w1,w2,···,Wn,-|||-则这个样本的平均数为 (omega )_(1)(overline {{x)_(1)}}^2+(omega )_(2)overline ({x)_(2)}+... +-|||-wnx^n,为了简化表示,引进求和符号,记作-|||-(omega )_(1)(overline {{x)_(1)}+(omega )_(2)overline ({x)_(2)}+... +(omega )_(n)overline ({x)_(n)}= __ .-|||-2.分层随机抽样的方差-|||-设样本中不同层的平均数分别为x1,x2,···,-|||-xn,方差分别为 ^21 ,dfrac (2)(2) ,..., ^2 ,相应的权重分-|||-别为w1,w2,···,wn,则这个样本的方差为-|||-^2= __ ,其中x为样本的-|||-平均数.-|||-3.百分位数-|||-(1)一般地,当总体是连续变量时,给定一个-|||-百分数 in (0,1) ,总体的p分位数有这样的1.分层随机抽样的平均数-|||-一般地,将样本a1,a 2,···,am和样本b1,b2,-|||-···,bn合并成一个新样本,则这个新样本的平-|||-均数为 dfrac ({a)_(1)+(a)_(2)+... (a)_(m)+(b)_(1)+(b)_(2)+... +(b)_(n)}(m+n)=-|||-dfrac (m)(m+n)cdot dfrac ({a)_(1)+(a)_(2)+... +(a)_(m)}(m)+dfrac (n)(m+n)cdot dfrac ({b)_(1)+(b)_(2)+... +(b)_(n)}(n)-|||-于是,当已知上述两层构成的样本中每层的-|||-平均数分别为x1和x2时,可得这个新样本-|||-的平均数为 dfrac (m)(m+n)(x)_(1)+dfrac (n)(m+n)(overline {x)}_(2) --|||-记 (omega )_(1)=dfrac (m)(m+n) (omega )_(2)=dfrac (n)(m+n) ,则这个新样本的-|||-平均数为 __ ,其中w1,w2称-|||-为权重.-|||-更一般地,设样本中不同层的平均数和相应-|||-权重分别为x1,x2,···,xn和w1,w2,···,Wn,-|||-则这个样本的平均数为 (omega )_(1)(overline {{x)_(1)}}^2+(omega )_(2)overline ({x)_(2)}+... +-|||-wnx^n,为了简化表示,引进求和符号,记作-|||-(omega )_(1)(overline {{x)_(1)}+(omega )_(2)overline ({x)_(2)}+... +(omega )_(n)overline ({x)_(n)}= __ .-|||-2.分层随机抽样的方差-|||-设样本中不同层的平均数分别为x1,x2,···,-|||-xn,方差分别为 ^21 ,dfrac (2)(2) ,..., ^2 ,相应的权重分-|||-别为w1,w2,···,wn,则这个样本的方差为-|||-^2= __ ,其中x为样本的-|||-平均数.-|||-3.百分位数-|||-(1)一般地,当总体是连续变量时,给定一个-|||-百分数 in (0,1) ,总体的p分位数有这样的
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