### Quantitative Variable

a variable that takes on a numerical value for which it makes sense to do arithmetic operations like averaging

### Type 2 Error

An error made by failing to reject (accepting) the null hypothesis when in fact it is false

### Law of large numbers

a property that states as the number of observations increases, the mean (statistic) of the observed values gets closer and closer to the true parameter

### p-value

the probability of observing a value for a test statistic as extreme or more than the hypothesized given value

### linear relationship

the relationship between two variables when the plotting of them in a scatterplot depicts a straight-line pattern

### data analysis

the method of collecting, organizing, and then describing data using graphs, numerical summaries in order to make statistical inferences

### extrapolation

the statistically unsound method of using a regression line to make predictions outside the range of values

### categorical variable

a variable that belongs to one of many levels or groups. A proportion is formed by counting how many of the observations belong to the individual groups.

### central limit theorem

as a randomly collected sample size gets large enough, the sampling distribution becomes more normal regardless of population distribution

### standard deviation

a numerical value that measures the spread of a distribution by looking at how far the observations are from the mean

### correlation

a numerical value that measures the strength and direction of the linear relationship between two quantitative variables

### lurking variable

a variable that has a significant effect on the response variable in the relationship between two variables in a study, but is not one of the two variables being studied

### Simpson's Paradox

this refers to a reversal of the direction of a comparison of an association when data from several groups are combined to form a single group

### double blind experiment

an experiment in which neither the subjects nor the people conducting the experiment know which treatment a subject receives

### power

the probability that a fixed level of significance will correctly reject a false null hypothesis

### undercoverage

this occurs when some groups in the population are left out of the process of choosing a sample

### Voluntary Response

a statistically unsound method of survey in which people choose themselves by responding to a general appeal

### Matched Pairs Design

an experiment in which the subjects are matched in pairs and each treatment is given to one subject in each pair

### Distribution

the pattern of a data set. It tells us the range of the variable, the frequency of each value, the center, and the shape (normal or skewed) of the data.

### Stratified Random Sample

a sample collected by dividing up the population into homogeneous groups and then using an SRS to sample from each group

### Robust

a confidence interval or the outcome of a significance test that is unchanged when the assumptions are violated OR a resistant statistical procedure

### Non-Response

this occurs when an individual chosen for a sample can't be contacted or refuses to cooperate

### Unbiased Statistic

a numerical value that is estimated from a sample distribution that is equal to the true value of the population (statistic=parameter)

### Random

a surveying or experimental phenomenon that occurs when the individual outcomes are uncertain

### Null Hypothesis

the statistical hypothesis that states that there is no effect or no change in the claimed population parameter

### Confidence Interval

an interval computed from sample data by a method that has a certain insurance of producing an interval containing the true population parameter

### Critical Value (upper)

a numerical value, z** or t** that has probability = p, lying to the right of it under the standard normal curve

### Treatment

a specific experimental condition applied to the units in order to change the environment to detect a significant effect

### Least Square Regression

the line that makes the sum of squares of the vertical distances of the data points from the lines as small as possible. Used for making predictions.

### Square of the Correlation

r-squared, the fraction of variation in the values of y that is explained by the least-squares regression of y on x