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聽濤月雨金蟲 (小有名氣)
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[求助]
一小段數(shù)據(jù)統(tǒng)計分析的描述,歡迎應(yīng)助
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A geometric mean provides a better estimate of central tendency for data that are distributed with a long tail at the upper end of the distribution. This type of distribution is common in the measurement of environmental chemicals in blood or urine. The geometric mean is influenced less by high values than is the arithmetic mean. Geometric means were calculated by taking the log of each concentration and then computing the weighted mean of those log-transformed values using SUDAAN software. Ninety-five percent confidence intervals around this weighted mean were calculated by adding and subtracting an amount equal to the product of a Student’s t-statistic and the standard error of the weighted mean estimate. The degrees of freedom of the t-statistic were determined by subtracting the number of strata from the number of primary sampling units (PSUs) according to the data available from the complex survey design. The standard error was computed with SUDAAN’s Proc Descript (design=WR), which uses Taylor series linearization for variance estimation. The weighted geometric mean and its confidence limits were then obtained by taking the antilogs of this weighted mean and its upper and lower confidence limits. [ 來自科研家族 快樂檢索 ] [ Last edited by 聽濤月雨 on 2012-11-12 at 11:11 ] |

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有愛的二哥
| 對于在頂端處有長間隔分布的數(shù)據(jù),幾何平均值可較好的估計該類數(shù)據(jù)的集中趨勢。通常,這類分布用來測量血液和尿液中的環(huán)境化學(xué)物。與算術(shù)平均值相比,幾何平均數(shù)更不易受大數(shù)值的影響。幾何平均數(shù)計算方法如下:取各濃度的log值,然后采用SUDAAN軟件計算經(jīng)log轉(zhuǎn)化后數(shù)值的加權(quán)平均數(shù)。通過加減學(xué)生t檢驗結(jié)果和加權(quán)平均數(shù)標準誤差的平均數(shù)來計算加權(quán)平均數(shù)的95%置信區(qū)間。依據(jù)復(fù)雜取樣設(shè)計中所取有效數(shù)據(jù),初級抽樣單位(PSUs)減去層數(shù)即為t-檢驗的自由度。采用SUDDAN Pro Descript(design=WR)計算標準誤差,其原理為泰勒級數(shù)線性方差估計。加權(quán)平均數(shù)的反對數(shù)值即為加權(quán)幾何平均數(shù),加權(quán)平均數(shù)的上部和下部界限即為其置信界限。 |
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