Appendix II

Introduction to Basic Statistics

STATISTICS

Statistics is the art and science of using numerical facts and figures. In Wikipedia, statistics is defined as a mathematical science pertaining to the collection, analysis, interpretation or explanation, and presentation of data.

There are three kinds of statistics:

- descriptive statistics;
- inferential statistics;
- causal modelling.

Descriptive statistics deals primarily with the description and interpretation of data by figures, graphs and charts.

Inferential statistics is the science of making decisions in the face of uncertainty by using techniques such as sampling and probability.

Causal modelling is part of inferential statistics. It is aimed at advancing reasonable hypotheses about underlying causal relationships between the dependent and independent variables.

In Six Sigma projects the most frequently used statistics is descriptive statistics, and the most useful distribution is the normal distribution.

Descriptive Statistics

- Data distribution: normal distribution, other distributions.
- Measures of central tendency: mean, median, mode.
- Measures of dispersion: standard deviation, variance and range.

Normal Distribution

Most data tends to follow the normal distribution, or bell-shaped curve. One of the key properties of the normal distribution is the relationship between the shape of the curve and the standard deviation.

99.73% of the area of the normal distribution is contained between –3 sigma and +3 sigma from the ...