CHAPTER 1: The Nature of Statistics

Descriptive statistics

Methods for organizing and summarizing information

Inferential Statistics

Uses sample data to make guesses about the bigger population

Population

Collection of all individuals or items you want to study

Sample

Part of the population where info is obtained

Observational study

Study where researches observe characteristics and take measurements

• help show association

• observing data that already exists

Designed experiment

Study where researchers actively change something and have controls THEN observe and take measurements

• shows causality

Census

Study that obtains info for the entire population of interest

• time consuming, costly, impractical

Representative sample

Sample that closely reflects the relevant characteristics of the population under consideration

Simple random sampling

Sampling procedure where each sample is equally likely to be obtained

Simple random sample

Sample obtained by simple random sampling

Simple random sampling with replacement (SRSWR)

member of the population can be selected more than once

• assume this unless specified

Simple random sampling without replacement (SRS)

member of population can be selected only once

Random number table

Outdated way to choose a random number using a book filled with random numbers

Random number generator

Computer program that selects a random number automatically

Systematic random sampling procedure

1. Divide the population size by the sample size. Round down to nearest whole number. This gets you m.

2. Use random number generator or table to pick a number between 1 and m. This will be k.

3. Select samples from members of k, k+m, k+2m…

• this method is easier to execute than simple random sampling

• Exception if there is some type of pattern in the population

Cluster sampling procedure

1. Divide the population into groups (clusters)

2. Obtain a simple random sample of clusters

3. Use members of cluster as the sample

Stratified Sampling procedure

1. Divide the population into subpopulations (strata)

2. From each stratum, obtain a simple random sample of the size proportional to the size of the stratum. (Sample size for a stratum equals the total sample size times the stratum size, divided by the population size)

3. Use all members obtained in step 2 as the sample.

Probability sampling

Process where a random device is used to choose which member of a population will be part of the sample