Chapter 1 Getting Started

What is Statistics?

Individuals vs. Variables

Individuals• People or objects included

in the study

Variables• Characteristic of the

individual to be measured or observed

Quantitative vs. Qualitative

Quantitative Variables• Have value or numerical

measurement for which operations such as addition or averaging make sense

Qualitative Variables• Describes an individual by

placing the individual into a category or group, such as male or female

Population vs. Sample

Population Data• Data is from every

individual of interest• Population Parameters are

numerical measures that describe an aspect of a population

Sample Data• The data are from only

some of the individuals of interest

• Sample Statistics are numerical measures that describe an aspect of a sample

Levels of Measurement

• Nominal – Names, Labels, Categories• Ordinal – Arranged in meaningful

mathematical order• Interval – Differences are meaningful• Ratio – Division or percentage comparisons

make sense; zero point

Chapter 1 Getting Started

1.2 Random Samples

Simple Random Sample (SRS)

• A simple random sample of no measurements from a population is a subset of the population selected in such a manner that every sample of size n from the population has an equal chance of being selected.

Random Number Tables (RNT)

• Used to help secure a SRS• Steps:– Number all members of the population

sequentially.– Drop a pin on the RNT to pick a starting point– Pull digits n at a time, discarding non-used

numbers– Repetition?

Other Methods to Secure a SRS

• Systematic• Stratified• Cluster• Multistage• Convenience

Systematic Sampling

• Population is numbered• Select a starting point at random and pick

every kth member

Stratified Sampling

• Divide population into distinct subgroups based on specific characteristics

• Draw random samples from each strata

Cluster Sampling

• Divide population into pre-existing segments or clusters (often geographic).

• Make a random selection of clusters.• All members of cluster are chosen.

Multistage Sampling

• Use a variety of sampling methods to create successively smaller groups at each stage.

• Final sample is made of clusters.

Convenience Sampling

• Create sample by selecting population members which are easily available