姑且先不说 t检验前提要求数据服从正态分布,以下两点需要注意:
- 注意点一:一般来讲,希望有80% 以上的统计功效(Statistical Power Level)假设检验才有效。
- 注意点二:另外,效应量(Effect Size,或R语言中为delta),反映处理效应大小的度量。即,两样本平均数的差异,一般delta=1。
- n :number of observations (per group).
补充:
power.t.test(power = 0.8,delta = 1,type = “paired”)
- n=9.937864
power.t.test(power = 0.8,delta =1,type = “paired”,alternative = “one.side”)
- n = 7.727622
power.t.test(power = 0.8,delta =1,type = “one.sample”)
- n = 9.937864
power.t.test(power = 0.8,delta =1,type = “one.sample”,alternative = “one.side”)
- n = 7.727622

—
power.t.test(n = 4, delta = 1)
Two-sample t test power calculation
n = 4
delta = 1
sd = 1
sig.level = 0.05
power = 0.2224633 # 样本数为4的话,统计功效very bad
alternative = two.sided
NOTE: n is number in each group
power.t.test(n = 20, delta = 1)
Two-sample t test power calculation
n = 20
delta = 1
sd = 1
sig.level = 0.05
power = 0.8689528 # 样本数为20 的话,统计功效 good
alternative = two.sided
NOTE: n is number in each group
power.t.test(power = 0.80, delta = 1)
Two-sample t test power calculation
n = 16.71477 # very important # 两样本双尾t test,至少每组17个样本
delta = 1
sd = 1
sig.level = 0.05
power = 0.8
alternative = two.sided
NOTE: n is number in each group
power.t.test(power = 0.80, delta = 1, alternative = “one.sided”)
Two-sample t test power calculation
n = 13.09777 # very important # 两样本单尾t test,至少每组13个样本
delta = 1
sd = 1
sig.level = 0.05
power = 0.8
alternative = one.sided
NOTE: n is number in each group
特定情况,比如:效用值(Effect Size或曰 delta)为2的时候
power.t.test(power = 0.80, delta = 2)
Two-sample t test power calculation
n = 5.090008 # 特定条件,效用值=2 的情况,双尾只需要至少每组 5个样本
delta = 2
sd = 1
sig.level = 0.05
power = 0.8
alternative = two.sided
NOTE: n is number in each group
power.t.test(power = 0.80, delta = 2, alternative = “one.sided”)
Two-sample t test power calculation
n = 3.987012 # 特定条件,效用值=2 的情况,单尾只需要至少 每组 4 个样本
delta = 2
sd = 1
sig.level = 0.05
power = 0.8
alternative = one.sided
NOTE: n is number in each group
参考:
2. Power calculations for one and two sample t tests.
4. 统计功效和效应值.
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