Differences

This shows you the differences between two versions of the page.

--- c:ms:2025:schedule:week06_t-test_and_anova_note [2025/04/10 01:22] – [t-test] hkimscil
+++ c:ms:2025:schedule:week06_t-test_and_anova_note [2025/04/13 23:35] (current) – [t-test, different approach] hkimscil
@@ Line 42: / Line 42: @@
   * 보정값은 샘플의 숫자마다 다르게 됨
   * <code>
+> # 아래는 샘플사지즈가 16일 경우
 > qt(0.025, df=15)
 [1] -2.13145
@@ Line 53: / Line 54: @@
 >
 </code>
-  * 혹은
+  * 혹은 계산한 t값이 2.8이 나왔다고 하면 (그리고 샘플사이즈가 16이라고 하면)
   * <code>
 > pt(2.8, df=15, lower.tail = F)
@@ Line 59: / Line 60: @@
 > pt(-2.8, df=15)
 [1] 0.006729863
+>
+> # 이 둘을 더한 값이 양쪽 날개 바깥쪽의 probability
+> 2 * pt(2.8, df=15, lower.tail = F)
+[1] 0.01345973
 >
 </code>
@@ Line 68: / Line 73: @@
 [1] -2.13145
 > qt(0.025, df=150000000000000)
+[1] -1.959964
+> # 샘플사이즈가 충분히 크면 qt값과 qnorm값이 동일한
+> # 1.96임을 주의
+> qnorm(0.025)
 [1] -1.959964
 >
@@ Line 453: / Line 462: @@
 abline(v = mean.a, lty=2, lwd=3, col="blue")
 abline(v = mean.b, lty=2, lwd=3, col="darkgreen")
+# or
+hist(A, xlim=c(0,50), ylim=c(0,8), col="red")
+hist(B, add=T, col=rgb(0, 1, 0, 0.5))
+abline(v=mean(dat), col="black")
+abline(v=mean(A), col="red")
+abline(v=mean(B), col="darkgreen")
 </code>
@@ Line 528: / Line 544: @@
 f.calculated.pvalue <- 1-pf(f.calculated, df1=df.between, df2=df.within)
 f.calculated.pvalue
+</code>
+<code>
+x <- rf(500000, df1 = df.between, df2 = df.within)
+hist(x,
+     breaks = "Scott",
+     freq = FALSE,
+     xlim = c(0, 7),
+     ylim = c(0, 3),
+     xlab = "",
+     main = "Histogram for a F-distribution
+     with df1 = 1 and df2 = 30",
+     cex.main = 0.9
+)
+curve(df(x, df1 = df.between, df2 = df.within),
+      from = 0, to = 8, n = 5000,
+      col = "red", lwd = 2,
+      add = T)
+abline(v=f.calculated, col="blue", lwd=2, lty="dotted")
+f.calculated.pvalue
+- f.calculated.pvalue
+</code>
+<code>
 # 한편,  t test를 했었을 때 (A, B 그룹을 가지고 independent
 # samples t-test를) 아웃 풋은
@@ Line 639: / Line 680: @@
 > abline(v = mean.b, lty=2, lwd=3, col="darkgreen")
 >
+> # or
+> hist(A, xlim=c(0,50), ylim=c(0,8), col="red")
+> hist(B, add=T, col=rgb(0, 1, 0, 0.5))
+> abline(v=mean(dat), col="black")
+> abline(v=mean(A), col="red")
+> abline(v=mean(B), col="darkgreen")
 </code>
 {{c:ms:2025:schedule:pasted:20250409-075631.png?550}}
+{{:c:ms:2025:schedule:pasted:20250414-083514.png?550}}
 <code>
 > # mean.total 에서 그룹a의 평균까지의 차이를 구한 후