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QBA
exam 2
47
Classics
10th Grade
03/15/2011

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Term
Simple linear regression
Definition
Analysis of the equational relationship between X and Y. Regression SS/Total SS
Term
Slope, B1
Definition
has a t distribution which standardizes its value to see if it is significantly different from 0. When the p-value of the slope is greater than the level of significance, one should assume the correlation coefficient will e close to 0.
Term
Y-intercept
Definition
B0, is not interpreted
Term
Correlation Coefficient
Definition
R, indicates nature and strength of the linear relationship variables
Term
Coefficient of determination
Definition
R2, the ration of explained variation in Y to the total variation.
Term
Least Squares Criteria
Definition
minimizes the squared vertical distances between the points and the regression line resulting in the line of best fit.
Term
Standard Error
Definition
will be smaller for better predictive equation. if the override value of y varies widely about the regression line, the standard error of the slope will be large.
Square root of the MS residual
Term
Correlation analysis
Definition
is the study of the nature and degree of the relationship between variables. A correlation coefficient of +1 or -1 means x and y are perfectly, linearly related. An r value of 0 indicates absolutely no relationship
Term
Extrapolation
Definition
is using Xs beyond the range of the given Xs to predict Y. THis can cause large errors in prediction. Relationship of slope to the correlation coefficient. signs are the same.
Term
Multicollinearity
Definition
when Xs are highly correlated-this gives redundant information.
Term
Heteroscedasticity
Definition
non-constant variance in the residuals
Term
Homoscedasticity
Definition
constant variance in the residuals
Term
Outliers
Definition
atypical values in a data set (anomalies)
Term
Non-Linear relationships
Definition
CURVILINEAR patterns or LOGARITHMIC relationships
Term
Multiple regression analysis includes
Definition
one dependent variable and more than one independent
Term
Stepwise
Definition
tries all combinations of variables and produces the best predictors in order of their predictive power.
Term
Artificially inflated R-squared occurs when..
Definition
there are too many predictors and not enough samples.
Term
Rule of thumb..
Definition
you should have at least 10 times the number of observations as predictor variables.
Term
Normal Probability plots
Definition
should produce a nearly straight line without outliers.
Term
T distribution vs. F Distribution
Definition
T is usedto test the individual coefficients where F tests the overall or "global" model.
Term
Residuals
Definition
are the differences in the observed value of Y at a given X and the predicted value. Absolute values between 2 and 3 are usually just suspicious while those over the absolute value of 3 are severe.
Term
Studentized Residuals
Definition
should fall within +/-3 in order to be considered normal values.
Term
Transform Y and/or X when...
Definition
any of the assumptions are violated
Term
In simple linear regression the use of regression lines is to ...
Definition
predict the average value of y that can be expected to occur at a given value of x.
Term
A high correlation between x and y..
Definition
does NOT prove that x causes y
Term
dependent variable plotted..
independent variable plotted...
Definition
vertical axis
horizontal axis
Term
If the confidence interval on the slope contains 0...
Definition
there is no significant relationship between x and y
Term
When R^2 is positive...
Definition
you CANNOT assume that the slope is also positive.
Term
The slope of the regression line represents...
Definition
the amount of change that is expected to take place in y when x increases by one unit.
Term
Extrapolation
Definition
using values beyond the range of the given Xs to predict Y
Term
if null hypothesis is rejected...
Definition
there is a relationship between x and y.
Term
if no correlation between two variables...
Definition
the regression line will be horizontal
Term
A large value for the slope does not necessarily imply a large value for the...
Definition
correlation coefficient.
Term
Test the individual coefficients to see which Xs are good predictors.
Definition
only test these if the overall model had at least one good predictor.
Term
A we add more predictors...
Definition
R2 increases
Term
When you re-run a model after taking out the poor predictor variables...
Definition
you have reduced the model
Term
When choosing between two models, both with good predictors for y...
Definition
choose the one with the smallest standard error.
Term
Check the correlation matrix to make sure the X variables...
Definition
are not correlated with each other
Term
check the signs of the coefficients...
Definition
to make sure they are logical.
Term
Never say x causes y unless it was...
Definition
a designed experiment.
Term
Qualitative variables in multiple regression are called..
Definition
dummy variables. do not interpret their coefficients
Term
If there is a curve in the scatter diagram for any x,y chart or the residuals use...
Definition
a quadratic equation... use x and x^2
Term
If you think two x variables may work together at different levels to affect y...
Definition
then try an interaction term.
Term
Only interpret the coefficients of...
Definition
good predictors and first order terms. First order terms are linear terms.
Term
Squared Xs and interacted Xs are called...
Definition
second order terms.
Term
The us of regression lines is to..
Definition
predict the average value of y that can be expected to occur at a given value of x.
Term
The study of the equational relationship between variables is called...
Definition
regression analysis.
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