[英]Plotting Growth Curve with Quadratic Growth
我想看看如何為我一直在運行的增長曲線模型繪制 R 中的二次增長。 模型:
m1 <- lmer(score ~ Time + Group + Time_Sqaure +
(1 + School | Subject), data=df, REML = FALSE)
tab_model(m1)
時間 (B = 9.58, p<.01) 和 Time_Square (B = - 0.51, p <.01) 以及組 (B = 2.77, p <.01) 差異均顯着。
如果我使用 plot_model,它會為我提供每個組的最佳擬合線。
plot_model(m1, type = "pred", terms = c("Time", "Group"))
有沒有辦法繪制擬合曲線或二次增長,以顯示增長速度隨時間放緩?
謝謝!
為了讓sjPlot::plot_model
了解發生了什么,您必須輸入Time_Square
作為I(Time^2)
而不是作為單獨的預測變量。
鑒於df$Time_Square <- df$Time^2
,以下兩個模型應該給你相同的結果:
m1 <- lmer(score ~ Time + Group + Time_Square +
(1 + School | Subject), data=df, REML = FALSE)
m2 <- lmer(score ~ Time + Group + I(Time^2) +
(1 + School | Subject), data=df, REML = FALSE)
但是,在第二個模型中,很明顯預測變量Time
輸入了兩次,因此在使用sjPlot::plot_model(...)
繪制時可以將其考慮在內。
為了確保,我使用以下模擬數據對其進行了測試:
library(dplyr)
grps <- 2 #number of groups
subj <- 100 #number of subjects within group
obs <- 10 #number of observations/times per subjects
b_0 <- 0 #overall intercept
b_1 <- 9.58 #linear time effect
b_2 <- -0.51 #quadratic time effect
sd_b0 <- 0.4 #SD of random intercept per subject
sd_b1 <- 3 #SD of random slope per subject
sd_b3 <- 1 #SD of group effect (you can simulate more than 2 groups)
sd_resid <- 10 #SD of residuals
df <- list(Group = factor(rep(letters[1:grps], each=obs*subj)),
Subject = factor(rep(1:subj, times=grps, each=obs)),
Time = rep(1:obs, times=subj*grps)
) %>% as.data.frame()
df$TimeSq <- df$Time^2
subj_b0 <- rnorm(subj, b_0, sd_b0) %>% rep(times=grps, each=obs)
subj_b1 <- rnorm(subj, b_1, sd_b1) %>% rep(times=grps, each=obs)
grp_m <- rnorm(grps, 0, sd_b3) %>% rep(times=, each=subj*obs)
df$Score <- with(df, subj_b0 + Time*subj_b1 + (Time^2)*b_2 + grp_m + rnorm(grps*subj*obs, 0, sd_resid))
fit1 <- lme4::lmer(Score ~ Time + I(Time^2) + Group + (Time | Subject), data=df)
sjPlot::plot_model(fit1, type="pred", terms=c("Time"))
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