T-Interval (t statistics)

T interval is good for situations where the sample size is small and population standard deviation is unknown.

When the sample size comes to be very small (n≤30), the Z-interval for calculating confidence interval becomes less reliable estimate. And here the…

Z-score (Standard Score / Normal Score)

Z stands for Standard Normal Distribution.
It's fairly important in real life: Japan use Z-score on exam to estimate each student's study skills.

Z-score is the essential concept of Z-Statistics.

Percentiles

Before start you probably need to know: explanations of percentiles are quite confusing and different from each teacher teaches and different at each website you searched. Because there is NO standard definition of percentile.

Empirical rule (68-95-99.7 Rule)

This rule ONLY applies to Normal Distribution.

It’s also called the 68-95-99.7% rule, because for a normal distribution:

• ≈68% of the data falls within 1 standard deviation of the mean

Chi-square Goodness-of-fit Test

Goodness-of-fit Test is good for testing a One-row Frequency Table.
The test shows how well certain…

Inference on Linear Regression

Conditions for inference on slope (L-I-N-E-R)