"大剂量服用维生素C无异于安慰剂，这是已经被双盲临床试验
所证明的了"
证明 is not an appropritae word for this.
In statistical hypothesis testing, you
have null hypothesis that megadose of vitamin
C is no different from placebo/or lowdaose
of vitamin C and alernative hypothesis megadose
C is different.
You draw conclusion based opon testing
given a significance level (conventionally
alpha=0.05).
if p-value >0.05, then you retain null hypothesis.
If p-value <0.05, then you reject null hypotehsis
and accept alternative hypothesis. Either way,
nothing is PROVED.
Alpha is arbitrarily detemriend as 0.05 purely due to
historical reasons. and even for teh same alpna,
rejection of hnull hypothesis is not proving.
Statistical conclsuion subject itself to type I and type II errors. Null hypothesis is retained
maybe due to small sample size which lead to smaller
power (defined as probability of rejecting null hypothesis when alternative is true)