1、什么是T test?
t-test：比较数据的均值，告诉你这两者之间是否相同，并给出这种不同的显著性（即是否是因为偶然导致的不同）
The t test (also called Student’s T Test) compares two averages (means) and tells you if they
are different from each other. The t test also tells you how significant the differences are;In
other words it lets you know if those differences could have happened by chance.
例子：制药公司可能想测试一种新的抗癌药物，看看它是否能提高预期寿命。在实验中，总有一个对照组(给一组人服用安慰剂，或“糖丸”)。对照组的平均预期寿命为+5岁，而服用新药的组的平均预期寿命为+6岁。看来这种药可能有效。但这可能是一个巧合。为了验证这一点，研究人员将使用Student’s t-test来发现结果是否可以在整个人群中重复
Student’s T-tests can be used in real life to compare means. For example, a drug company may
want to test a new cancer drug to find out if it improves life expectancy. In an experiment,
there’s always a control group (a group who are given a placebo, or “sugar pill”). The control
group may show an average life expectancy of +5 years, while the group taking the new drug
might have a life expectancy of +6 years. It would seem that the drug might work. But it could
be due to a fluke. To test this, researchers would use a Student’s t-test to find out if the
results are repeatable for an entire population.
2、The T Score.
T Score：是两组之间的差异与组内差异的比值。t值越大，组间差异越大。t值越小，组间的相似性越大。t得分为3表示两个组之间的差异是它们内部差异的三倍。当您运行t测试时，t值越大，结果越有可能是可重复的
The t score is a ratio between the difference between two groups and the difference within the
groups. The larger the t score, the more difference there is between groups. The smaller the t
score, the more similarity there is between groups. A t score of 3 means that the groups are
three times as different from each other as they are within each other. When you run a t test,
the bigger the t-value, the more likely it is that the results are repeatable
- A large t-score tells you that the groups are different.
- A small t-score tells you that the groups are similar
3、T-Values and P-values
P-values：“足够大”有多大?每个t值都有一个p值。p值是样本数据的结果偶然发生的概率。p值从0%到100%。它们通常写成小数。例如，5%的p值是0.05。低p值是好的;它们表明您的数据不是偶然产生的。例如，p值为0.01意味着实验结果碰巧发生的概率只有1%。在大多数情况下，p值为0.05(5%)表示数据有效
How big is “big enough”? Every t-value has a p-value to go with it. A p-value is the probability
that the results from your sample data occurred by chance. P-values are from 0% to 100%.
They are usually written as a decimal. For example, a p value of 5% is 0.05. Low p-values are
good; They indicate your data did not occur by chance. For example, a p-value of .01 means
there is only a 1% probability that the results from an experiment happened by chance. In
most cases, a p-value of 0.05 (5%) is accepted to mean the data is valid.
4、main types of t-test
An Independent Samples t-test compares the means for two groups.
A Paired sample t-test compares means from the same group at different times (say, one year apart).
A One sample t-test tests the mean of a single group against a known mean.