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Statistics
The collection, organization, and interpretation of data for the purposes of summarization (descriptive statistics) pool drawing conclusions about populations based on samples (inferential statistics)

Population
A collection of objects together with a certain characteristic; precisely defined collection of values

Sample
Part of a population

Inference
Decision making based on samples drawn from populations

Random sample
Each and every member of the population has an equal chance of being selected

Internal validity
The certainty that the observations in our sample group are accurate measurements (something that is not internally valid doesn't actually change the characteristic being observed)

External validity
The certainty that the methods and presence of the researcher is not affecting what is being studied

Valid random sample
A random sample that is both internally and externally valid

The arithmetic mean or average value of a population

Sample average is approximately equal to the population average

Mean
Sum of all values divided by the number of values

Median
The middle value when data is ordered from lowest to highest
*if there are two middle values, we average the two

Mode
The most frequently occurring observation
*There can be no mode or multiple modes

Modal class
The mode for grouped data

Range
The difference between the highest and lowest value in the data set

Standard deviation
A form of average distance from the mean

Working backward
If we know the percentage of data between 0 and z, we look up this area (in decimal form) in the table and determine the closest z value (choose higher value if midway)

