[英]R - pairwise_t_test Test Statistics Unchanged When Switching Between Pooled Standard Deviation and non-Pooled Stardard Deviation
While reviewing pairwise t-tests as a post hoc for one way repeated measures ANOVA I noticed an oddity.在回顾成对 t 检验作为单向重复测量方差分析的事后,我注意到一个奇怪的地方。 The test statistic for pair_t_test in the rstatix library does not change when I pool the standard deviation -- in fact none of the output changes.
当我合并标准偏差时,rstatix 库中 pair_t_test 的测试统计数据没有改变——事实上,output 都没有改变。
My understanding is that the whole point of pooling the standard deviation is to more accurately estimate the test statistic.我的理解是,汇集标准差的重点是更准确地估计检验统计量。 However, while trying this out I can't find a difference in the output (see below).
但是,在尝试此操作时,我找不到 output 的区别(见下文)。
Is my understanding incorrect?我的理解不正确吗? What effect should a pooled standard deviation have on multiple pairwise comparisons (sphericity notwithstanding)?
合并标准差对多个成对比较(尽管有球形度)有什么影响?
I used the following data setup:我使用了以下数据设置:
library(rstatix)
library(tidyverse)
selfesteem.test <- selfesteem %>%
gather(key = "time", value = "score", t1, t2, t3) %>%
convert_as_factor(id, time)
With pooled standard deviation in the following code:在以下代码中使用合并标准差:
selfesteem.test %>%
pairwise_t_test(
score ~ time,
paired = TRUE,
p.adjust.method = "bonferroni",
pool.sd = TRUE
)
Resulting in:导致:
# A tibble: 3 x 10
.y. group1 group2 n1 n2 statistic df p p.adj p.adj.signif
* <chr> <chr> <chr> <int> <int> <dbl> <dbl> <dbl> <dbl> <chr>
1 score t1 t2 10 10 -4.97 9 0.000772 0.002 **
2 score t1 t3 10 10 -13.2 9 0.000000334 0.000001 ****
3 score t2 t3 10 10 -4.87 9 0.000886 0.003 **
The following code:以下代码:
selfesteem.test %>%
pairwise_t_test(
score ~ time,
paired = TRUE,
p.adjust.method = "bonferroni",
pool.sd = FALSE
)
Results in the same:结果相同:
# A tibble: 3 x 10
.y. group1 group2 n1 n2 statistic df p p.adj p.adj.signif
* <chr> <chr> <chr> <int> <int> <dbl> <dbl> <dbl> <dbl> <chr>
1 score t1 t2 10 10 -4.97 9 0.000772 0.002 **
2 score t1 t3 10 10 -13.2 9 0.000000334 0.000001 ****
3 score t2 t3 10 10 -4.87 9 0.000886 0.003 **
According to ?pairwise_t_test
根据
?pairwise_t_test
Pooling does not generalize to paired tests so pool.sd and paired cannot both be TRUE.
池化不能推广到配对测试,因此 pool.sd 和paired 不能都为TRUE。
If pool.sd = FALSE the standard two sample t-test is applied to all possible pairs of groups.
如果 pool.sd = FALSE,则标准二样本 t 检验适用于所有可能的组对。 This method calls the t.test(), so extra arguments, such as var.equal are accepted.
此方法调用 t.test(),因此接受额外的 arguments,例如 var.equal。
Also, the Usage does show the negation ( !
)此外,用法确实显示否定(
!
)
pairwise_t_test( data, formula, comparisons = NULL, ref.group = NULL, p.adjust.method = "holm", paired = FALSE, pool.sd =,paired, detailed = FALSE. ... )
pairwise_t_test(数据,公式,比较 = NULL,ref.group = NULL,p.adjust.method = “holm”,配对 = FALSE,pool.sd =,配对,详细 = FALSE。...)
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