中介效应的定义

如果自变量X通过某一变量M对因变量Y产生一定影响，则称M为X和Y的中介变量。研究中介作用的目的是在已知X和Y关系的基础上，探索产生这个关系的内部作用机制。作用关系图如下：

X对Y的总效应分为直接效应（direct effect）和间接效应(indirect effect)，直接效应是指当中介变量（M）固定在某一水平时，自变量X对结局变量Y的效应。间接效应是指自变量X通过中介变量M对结局变量Y施加的影响。按上图所示则c为直接效应，间接效应则为a与b的结合。 根据Baron和Kenny等人的研究，符合以下标准的变量可以判定为中介变量： 1）暴露水平的变化显著影响中介变量水平的变化（即X与M的关联具有统计学意义）。

2）中介变量水平的变化显著影响结局变量（即M与Y的关联具有统计学意义）。

3）暴露因素水平的变化显著影响结局变量（即X与Y的关联具有统计学意义）。

通常情况下标准1）和标准2）被普遍接受，标准3）未被接收，理由是当直接效应和中介效应的作用方向相反时，X与Y间的关联可能无统计学意义，但不能否认中介效应的存在。

2.中介效应的R实现

#mediation包中的mediate函数
install.packages("mediation")
library(mediation)
data(jobs)
b <- lm(job_seek ~ treat + econ_hard + sex + age, data=jobs)
c <- lm(depress2 ~ treat + job_seek + econ_hard + sex + age, data=jobs)
contcont <- mediate(b, c, sims=50, treat="treat", mediator="job_seek")
summary(contcont)
plot(contcont)

ACME: stands for average causal mediation effects.间接因果效应，表示X通过M对Y的效应大小 通过med.sum$d0和med.sum$d0.p可以获得ACME的效应和p值 ADE：stands for average direct effects.直接效应，表示X直接对Y的作用大小 通过med.sum$z0和med.sum$z0.p可以获得ADE的效应和p值 Total Effect: stands for the total effect (direct + indirect) of the IV on the DV. X对Y的直接和间接作用总和 Prop. Mediated: describes the proportion of the effect of the IV on the DV that goes through the mediator. X通过M对Y的作用的比例

library(mediation)
library(ggplot2)
library(dplyr)

#结果说明
#ACME stands for average causal mediation effects.间接因果效应，表示X通过M对Y的效应大小
#通过med.sum$d0和med.sum$d0.p可以获得ACME的效应和p值
#ADE stands for average direct effects.直接效应，表示X直接对Y的作用大小
#通过med.sum$z0和med.sum$z0.p可以获得ADE的效应和p值
#Total Effect stands for the total effect (direct + indirect) of the IV on the DV. X对Y的直接和间接作用总和
#Prop. Mediated describes the proportion of the effect of the IV on the DV that goes through the mediator. X通过M对Y的作用的比例


setwd("/Users/vincent/Documents/Rscript/mediation/project")
data = read.table("data.txt",header = T,sep = "\t" ,fileEncoding = "UTF-8")
#View(data)
names(data)
alphadata <- read.table("alpha_diversity_index.sample.txt",header = T,sep = "\t")



# 假设data1是第一个数据集，data2是第二个数据集
# 为了统一列名，将第二个数据集的"结题样本名称（中肛）"列重命名为"Sample_Name"
data <- data %>%
  rename(Sample_Name = "结题样本名称.早唾.")

# 使用left_join()函数将两个数据集合并在一起，基于"Sample_Name"列
merged_data <- left_join(data, alphadata, by = "Sample_Name")
View(merged_data)
names(merged_data)
# merged_data 中包含了合并后的数据

#总体思路：生活方式数据为自变量、扩增子为中介变量（chao1        dominance       goods_coverage  observed_features       pielou_e        shannon simpson）、结局为因变量（GDM    BMI     LGA     PROM），基线和检验指标作为调节变量（协变量）
#中介变量：α指数、差异菌群都分析

#生活方式 smoking2      alcohol2        physical2       EPDS2   depression2     PASQ2   sleep2  calorie2        animal2 plant2  vitamin2        beverages2      bean2   folate2 multivit2       VitD2   Ga2     Fe2     DHA2    DF2     probiotics2
# 中间变量  chao1       dominance       goods_coverage  observed_features       pielou_e        shannon simpson
# 结局为因变量（GDM     BMI     LGA     PROM）
# 基线和检验指标作为调节变量 
# 基线 ：week   sex     GWG     BMI     height  education       register        parity  race    unplanned       unemployment
# 检验指标 ：FBG        TC      HDL     TG      LDL     HCY     TT3     TT4     FT3     FT4     ATPa    TSH     A       E       25-OH-D3


merged_data$GDM <- ifelse(merged_data$GDM == "control", 0, 1)
merged_data$BMI <- ifelse(merged_data$BMI == "control", 0, 1)
merged_data$LGA <- ifelse(merged_data$LGA == "control", 0, 1)
merged_data$PROM <- ifelse(merged_data$PROM == "control", 0, 1)


mlist <- c("smoking1", "alcohol1", "physical1", "depression1", "sleep1", "calorie1", "animal1", "plant1", "vitamin1", "beverages1", "bean1", "diet1", "health1")
length(mlist)
xlist <- c("chao1", "dominance", "goods_coverage", "observed_features", "pielou_e", "shannon", "simpson")

ylist <- c("GDM")

covlist <- c("GWG", "BMI", "height", "education", "register", "parity", "race", "unplanned", "unemployment")

output_path <- "/Users/vincent/Documents/Rscript/mediation/project/X101SC21124468-Z01-F003-早唾GDM/result/"
if (!file.exists(output_path)) {
  # 如果目录不存在，创建它
  dir.create(output_path, recursive = TRUE)
  cat("目录已创建：", output_path, "\n")
} else {
  cat("目录已经存在：", output_path, "\n")
}
# 循环执行中介效应分析
for (x_var in xlist) {
  for (m_var in mlist) {
    for (y_var in ylist) {
      tryCatch({
      # 创建文件名
      output_file <- paste(paste(output_path, "自变量",x_var,sep = ""), paste("中间变量",m_var,sep = ""), paste("因变量",y_var,sep = ""), ".txt", sep = "_")
      # 构建模型
      b_int <- lm(paste(m_var, "~", x_var, "+", paste(covlist, collapse = " + "), sep = " "), data = merged_data)
      d_int <- lm(paste(y_var, "~", x_var, "+", m_var, "+", paste(covlist, collapse = " + "), sep = " "), data = merged_data)

      # 进行中介效应分析
      
      contcont_result <- mediate(b_int, d_int, sims = 50, treat = x_var, mediator = m_var)
      output_file_name <- paste(paste(output_path, "自变量",x_var,sep = ""), paste("中间变量",m_var,sep = ""), paste("因变量",y_var,sep = ""), ".pdf", sep = "_")
      #png(output_file)  # 设置图像的宽度和高度
      pdf(output_file_name, width = 8, height = 6)
      plot(contcont_result)  
      
      dev.off()  
      # 将结果输出到文件
      result_text <- suppressWarnings(capture.output(summary(contcont_result)))
      writeLines(result_text, con = output_file)
      #write.table(summary(contcont_result), file = output_file)
            
      }, error = function(e) {
        # 处理异常的代码块
        cat("An error occurred:", conditionMessage(e), "y is ", y_var , "x is ", x_var, "m is ", m_var ,"\n")
        # 这里可以添加其他处理逻辑，或者略过错误
      })
    }
  }
}