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Statistics
stats 221 exam 2 part 2
36
Mathematics
Undergraduate 2
03/13/2008

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Term
regression equation
Definition
a formula for a line that models a linear relationship between two quantitative variables
Term
residual
Definition
the observed y mines the predicted y; denoted y - yhat
Term
residual plot
Definition
a plot that show how well the regression line fits the data; complete scatter plot in a shoebox form is good,
Term
megaphone
Definition
the shape in a residual plot that means there is unequal variance in the y's across all levels of x (the standard deviation doesn't stay the same)
Term
smile or frown
Definition
the shape in a residual plot that means the data is not linear
Term
sample mean x bar
Definition
the random variable of the sampling distribution of x bar
Term
sample space
Definition
the list of all possible outcomes of a random phenomenon
Term
sampling distribution of x bar
Definition
a distribution of all possible x bars from all possible samples
Term
sampling variablility
Definition
the variability of sample results from one sample to the next; something we must measure in order to effectively do inference
Term
scatterplot
Definition
a two dimensional plot used to examine strength of relationship between two variables as well as direction and type of relationship
Term
significance level (alpha)
Definition
the risk (probability) of incorrectly rejecting a true null hypothesis. when p is low reject Ho and conclude that Ha is correct
Term
simple conditions for inference
Definition
SRS, population normally distributed and sigma known
Term
Simpson's paradox
Definition
when percentages in a two way table reverse because a third (lurking) variable is ignored (Larry Bird and free throws)
Term
simulation
Definition
using random numbers to imitate chance behavior
Term
slope
Definition
a measure of the average change in the response variable (Y) for every one unit increase in the explanatory variable (X)
Term
standard deviation s
Definition
a measure of the variability of the data in a sample about x bar
Term
standard deviation of x bar (also called standard deviation of the sampling distribution of x bar)
Definition
a measure of the variability of the values of the statistic x bar about mu; computed as sigma over the square root of n.
Term
statistic
Definition
a number computed from sample data (without any knowledge of the value of a parameter) used to estimate the value of a parameter
Term
statistic symbols
Definition
x bar, s, p hat: mean of a sample, standard deviation of a sample, proportion of a sample
Term
statistical process control
Definition
a procedure used to check a process at regular intervals to detect problems and correct them before they become serious.
Term
statistically significant
Definition
results of a study that differ too much from what we expected (if Ho were true) because of randomization to attribute to chance variation; the difference between the observed statistic and the claimed parameter value is too large to be due to chance. Happens when p value is lower than alpha
Term
sum of squared residuals
Definition
the residuals are squared and added; denoted SSE
Term
test of significance
Definition
procedure used to assess the evidence against a claim (hypothesis) about the value of a parameter
Term
test statistic
Definition
a number that summarizes the data for a test of significance; usually used to obtain p value
Term
total variation in Y
Definition
the sum of the squared deviations of the Y observations about their mean, y-bar
Term
two-sided alternative
Definition
a type of alternative hypothesis where the researcher is interested in deviations in both directions
Term
two-way table
Definition
a table containing counts for two categorical variables. it has r rows and c columns.
Term
unbiased
Definition
a condition where the mean of the statistic values equals the parameter that the statistic estimates
Term
unexplained variation
Definition
the sum of squared residuals
Term
X (capital X)
Definition
the symbol for explanatory variable
Term
x-bar chart
Definition
a plot of sample means over time used to assess whether a process is in control
Term
Y (capital Y)
Definition
the symbol for response variable
Term
y-hat
Definition
the symbol for predicted y
Term
z*
Definition
the z-value obtained from table C corresponding to a desired level of confidence; used in computing a confidence interval
Term
z-score
Definition
a measure of the number of standard deviations of a value or observation from the mean
Term
zero or one
Definition
the probability that the value of the parameter mu is in the confidence interval. OR the probability that the null hypothesis is true
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