假陽性與假陰性權衡圖

我正在做一個決策分析，我試圖用 R 來說明假陽性（假通過）與假陰性（假不通過）之間的權衡。我創建了一個帶有零假設和備擇假設的密度圖曲線，但想通過這些示例圖進一步說明關系。非常感謝您在創建示例 1 和 2（尤其是示例 1）時提供的幫助。謝謝！

密度圖

示例 1

示例 2

uj5u.com熱心網友回復：

我使用了兩個偏移正態分布，前提是你能想象到的任何曲線。

library(ggplot2)

xs <- seq(-2, 4, length.out = 201)
dat <- do.call(rbind,
  list(data.frame(x=xs, y=dnorm(xs), id="1"),
       data.frame(x=xs, y=dnorm(xs, 2), id="2")))

情節 1

vline <- 1
eps <- 1e-3

ggplot(dat, aes(x, y, group = id, color = id))  
  geom_line()  
  geom_area(aes(fill = id),
            data = ~ subset(., (id == "1" & x > (vline eps)) | (id == "2" & x < (vline-eps))))  
  geom_vline(xintercept = vline, linetype = "dashed")  
  labs(x = "Hazard Ratio", y = NULL)  
  guides(color = "none", fill = "none")  
  theme_classic()  
  theme(
    axis.line.y = element_blank(),
    axis.text.y = element_blank(),
    axis.ticks.y = element_blank()
  )

這vline是這里的區分線，如果它不在交叉點處，那么它仍然有用。例如，

vline <- 1.2

情節2

rng <- c(0.75, 0.85)
rngdat <- do.call(rbind,
  by(dat, dat$id, function(z) with(z, data.frame(approx(x, y, xout = rng), id = id[1]))))
rngdat$otherx <- fifelse(rngdat$id == "1", Inf, -Inf)

ggplot(dat, aes(x, y, group = id, color = id))  
  geom_line(na.rm = TRUE)  
  geom_segment(aes(xend = x, yend = 0),
               data = subset(rngdat, id == 1),
               color = "black", linetype = "dashed")  
  geom_segment(aes(xend = otherx, yend = y),
               data = rngdat, linetype = "dashed")  
  coord_cartesian(xlim = c(0, 2))  
  scale_x_continuous(name = "HR gate")  
  scale_y_continuous(
    name = "False Go Probability",
    sec.axis = sec_axis(~ ., name = "False No-Go Probability"))  
  scale_color_manual(values = c("1" = "blue", "2" = "red"))  
  guides(color = "none")  
  theme_classic()  
  theme(
    axis.line.y.left = element_line(color = "red"),
    axis.line.y.right = element_line(color = "blue")
  )

情節 3

offset <- max(rngdat$y[rngdat$id == "1"])   0.1
cutoff <- 0
dat <- transform(
  dat,
  yoff = ifelse(id == "1", 0.05   offset, 0),
  cat = ifelse(id == "1",
               ifelse(x < cutoff, "True Positive", "False Negative"),
               ifelse(x < cutoff, "False Positive", "True Negative")))

ggplot(dat, aes(x, y = y   yoff))  
  geom_ribbon(aes(ymin = yoff, ymax = y   yoff,
                  group = cat, fill = cat, alpha = cat),
              na.rm = TRUE)  
  geom_vline(xintercept = cutoff)  
  scale_fill_manual(
    name = NULL,
    values = c("True Positive" = "red", "False Negative" = "red",
               "False Positive" = "blue", "True Negative" = "blue"))  
  scale_alpha_manual(
    name = NULL,
    values = c("True Positive" = 1, "False Negative" = 0.2,
               "False Positive" = 0.2, "True Negative" = 1))  
  labs(x = NULL, y = NULL)  
  theme(
    legend.position = "bottom",
    axis.text.y = element_blank(),
    axis.ticks.y = element_blank()
  )

uj5u.com熱心網友回復：

看起來您的癥結在于弄清楚如何在給定的 x 或 y 值下訪問密度曲線的值。

您可以使用來訪問由函式構造ggplot_build()的底層。這里有一些進一步的討論。data.framegeom_density

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