如何用R语言构建边际结构模型,请给出代码示例
时间: 2024-02-22 13:56:14 浏览: 25
以下是用R语言构建边际结构模型的示例代码:
首先,我们需要安装并加载必要的包,例如`tidyverse`和`margins`:
```
install.packages("tidyverse")
install.packages("margins")
library(tidyverse)
library(margins)
```
然后,我们需要准备数据,假设我们有一个名为`data`的数据框,其中包含观察值、干预、时间、结果和混淆因素等变量。我们需要对数据进行整理和转换,以便使用`msm`函数进行建模。下面是一个示例代码:
```
data %>%
arrange(observation, time) %>%
mutate(id = group_indices(., observation)) %>%
mutate(intervention_time = ifelse(intervention == 1, time, NA)) %>%
fill(intervention_time) %>%
mutate(intervention_time = ifelse(intervention_time == max(time), NA, intervention_time)) %>%
mutate(time_since_intervention = time - intervention_time) %>%
select(id, time_since_intervention, intervention, result, confounder1, confounder2, ...) -> data_msm
```
接下来,我们可以使用`msm`函数来拟合边际结构模型。我们需要指定模型公式和权重变量(在这里是`time_since_intervention`)。下面是一个示例代码:
```
model <- msm(result ~ intervention + confounder1 + confounder2 + ...,
subject = "id",
time = "time_since_intervention",
weights = "time_since_intervention",
data = data_msm)
```
最后,我们可以使用`margins`函数来计算边际效应和边际效应差异,并进行图形化展示。下面是一个示例代码:
```
margins(model, at = list(intervention = c(0, 1))) %>%
summary() %>%
plot()
```