##### AP Statistics Terms 2
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#### Complete List of Terms and Definitions for AP Statistics Terms 2

Terms Definitions
1 unimodal having one mode
2 Se Standard deviation of residuals
Resistant Not affected by extreme values.
blinding any individual associated with an experiment who is not aware of how subjects have been allocated to treatment groups
trial the sequence of several components representing events that we are pretending will take place
Range The difference between the smallest and largest numbers in a data set
Correlation Correlation measures the strength and direction of the linear relationship between two quantitative variable. Correlation is usually written as r.
Suppose we have data on variables x and y for n individuals. The values for the first individ. are X1 and Y1, second individ. X2, Y2, and so on. The means and SD of the two variables are x-bar and Sx, for the x values and y-bar Sy for the y-values. The correlation r between x and y is:
r = [1/(n-1)][∑((x - xbar) / Sx)((y - ybar) / Sy)
r only measures straight-line relationships.
3 Placebo A treatment that has no effect
simulation models random events by using random numbers to specify event outcomes with relative frequencies that correspond to the true real-world relative frequencies we are trying to model
distribution gives the possible values of the variable and the frequency or relative frequency of each value
extrapolation although linear models provide an easy way to predict values of y for a given value of x, it is unsafe to predict for values of x far from the ones used to find the linear model equation; predictions should not be trusted
slope the change in the predicted response variable for every unit increase in the explanatory variable
complement rule the probability that something will not happen is 1 - probability that it will happen
shape one of three ways to describe distributions; terms like 'normal, symmetric, skewed, binomial' describe this
Modified boxplot Outliers are plotted as isolated points; whiskers reach to the second-most outlying value.
Probability The proportion of times the event occurs in many repeated trials of a random phenomenon.
3 Undercoverage When part of a population is represented less tan another
Individuals The objects described by a set of data.
statistically significant when an observed difference is too large for us to believe that is is likely to have occurred naturally
census a sample that consists of the entire population
frequency table lists the categories for a categorical variable and displays the counts for each category
response variable values of this variable record the results of each trial with respect to what we were interested in
roundoff error the error that occurs when the percents don't add up to 100%
categorical variable places an individual into one of several groups or categories
Boxplot Center in a boxplot ends at the quartiles and spans the middle portion of the observations. Middle vertical line markes the M, whiskers extend to largest and smallest observations.
4 Confidence interval An interval used for estimating a parameter
Pth Percentile The value such that p percent of observations fall at or below it.
nonresponse bias bias introduced to a sample when a large fraction of those sampled fails to respond
clusters these form when there is a gap between the data
time pot type of plot used to measure a variable over time; time goes on x-axis
Standard normal distribution The SND is the normal distribution N(0,1) with mean 0 and SD 1. If a variable x has any normal distribution N(μ,σ) with mean μ and SD σ, then the standardized variable: z = (x - μ) / σ has the standard normal distribution.
3 Systematic Sample A sample drawn by taking every nth person
addition rule If A and B are disjoint events, the probability of A or B is P(A) + P(B)
simple random sampling design in which each set of n elements in the population has an equal chance of selection
Skewed to the left Left side of the histogram extends much farther out than the right side.
4 Law of Large Numbers The long run probability will approach its theoretical probability
degrees of freedom the number n-1 is called this of the variance or standard deviation
3 Simple Random Sample (SRS) sample size where each element has an equal chance of being selected
Density curve mean and median The median of a density curve is the equal-areas point, the point that divides the area under the curve in half. The mean of a density curve is the balance point, at which the curve would balance if made solid material. (For a symmetric density curve mean = median and are both in the middle.