What is statistics?

1. Statistics is the science of collecting, organizing, presenting, analyzing, and interpreting data to assist in making more effective decisions.
2. There are two type of statistics:
1. Descriptive statistics are procedure used to organize and summarize data.
2. Inferential statistics involve taking a sample from a population and making estimates about a populations based on the sample results.
1. A population is an entire set of individuals or objects of interest or the measurements obtained from all individuals or objects of interest.
2. A sample is a part of the population.
3. There are two types of variables:
1. A qualitative variable is non numeric:
   1. Usually we are interested in the number or percent of the observations in each category.
   2. Qualitative data are usually summarized in graphs and bar charts.
2. There are two types of quantitative variables and they are usually reported numerically :
   
1. Discrete variables can assume only certain values, and there are usually gaps between values.
2. A continuous variable can assume any value within a specific range.
4. There are four level of measurement:
1. With the nominal level, the data are sorted into categories with no particular order to the categories.
1. The categories are mutually exclusive. An individual or object appears in only one category.
1. The categories are exhaustive. An individual or object appears in at least one of the categories.
2. The ordinal level of measurement presumes that one classification is ranked higher than another.
3. The interval level of measurement has the ranking characteristic of the ordinal level of measurement plus the characteristic that the distance between values is a constant size.
4. The ratio level of measurement has all characteristics of the interval level, plus there is a zero point and the ratio of two values is meaningful.