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威望 旺
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又仔细看了一下统计分析部分和讨论部分。
统计分析时,作者是在线性回归的基础上依次分别纳入协变量进行分析的。
Linear regression models were performed between the C:T3 ratios of PFASs (PFAS transfer efficiencies) and possible covariates (factors of transfer efficiency). Because of a skewed distribution, the C:T3 ratios were natural log (ln) transformed to better achieve the normality assumption of linear models. The following covariates were included one at a time: maternal age (continuous), prepregnancy BMI [underweight (<18.5), normal (18.5–23.9), overweight (≥24 kg/m2), categorical], gestational week (continuous), household income (<50 K, 50–100 K, ≥100 K yuan per year, categorical), maternal education (higher than high school, high school, less than high school, categorical), employment (unemployed and employed, dichotomous), parity [0 (nulliparous) and ≥1 (multiparous), dichotomous], infant gender (male and female, dichotomous), passive smoking status (yes and no, dichotomous), GFR (continuous), and serum albumin (continuous). Levels of GFR and serum albumin were also divided into tertiles with the lowest category used as reference. The beta coefficient from the linear model was used to calculate the percentage change in the PFAS transfer efficiencies for each factor [percentage change = (eβ – 1) × 100%].
其实这里,私以为可以做多元线性回归,然后筛选变量,并检查一下高学历和高生育年龄之间的共线性;也可以通过协方差分析,剔除高生育年龄影响之后,看单纯高学历(无生育年龄差异影响)对胎盘转移效率的影响。
讨论部分,作者认为这种影响无法解释,可能是高学历者有晚育趋势,另外,也可能是低学历组例数太少导致的选择偏倚。
Mothers with higher education tended to have higher transfer efficiency (Table 4). It is difficult to explain how education attainment could affect PFAS transfer; however, it may be partly due to the positive relationship between maternal age and education attainment (higher educated women have a tendency to give birth later). Insufficient sample size of low educated mothers [less than high school (n = 8)] might be another reason, resulting in selection bias. |
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