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BIT 3434 Exam 2 Questions And Accurate Answers
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BIT 3434 Exam 2 Questions And Accurate AnswersWhat does the mathematical form of a regression model take? Y= B0 + B1X1i + Ei; E
random disturbance or error How does a math form of regression differ from a
regression function? Regression MODEL based off data where as the Regression
FUNCTION is based off our sample
What is the concern if we try to fit all data points into a regression model? -Answer
Overfitting: looking too closely at a sample of data, to discover characteristics of the
sample that are not representative of the population from which the sample was drawn.
What might Overfitting lead to? - Answer This might lead to incorrect inference about
the population being sampled includes misguided coefficients, R squared and p values.
What is the equation for the prediction interval? (Note: not how to calculate standard
prediction error) - Answer Y +- 2*Se (where Se = standard error)
What is the equation of the regression line after the regression model has been fitted?
-Answer It depends on what regression model has been used. It would be y = a +bx for
linear regression, y = a + bx + bx^2 + bx^3. for polynomial and y = a +b*e^(x) for log
regression.
How to find the best model among various models? - Answer Among various models, we
find the best model when there is multiple independent variables by checking the
adjusted r squared
Use the notation of ^Y
What is "Best Fit"? - Answer Best fit: minimize the sum of squares of error or make r
squared as close to 1 as possible
, How does the standard error of regression differ from the standard error of a
coefficient? - Answer Standard error of the regression- Average distance of variability
between actual and estimated value of y.
Standard error of coefficient - how close the regression function's coefficients are to the
actual, unknown coefficients.
How would we interpret the coefficient? - Answer how close the regression function's
coefficients are to the actual, unknown coefficients.
Interpretation of standard error of the coefficient- Answer The smaller the standard
error of the coefficient the closer to the real value the coefficient is. If p-value is less
than the critical value (probably .05), then that coefficient is statistically significant and
is not just 0.
How do we interpret the log-transformed variable? Note: when both sides are log
transformed - Answer Multiplicative change in independent variable = Multiplicative
change in dependent variable
Change multiplication to addition
How do we interpret the coefficient for an interaction term? - Answer The rise in
effectiveness of x1 for a 1 unit change in x2, and vice-versa
How to make a prediction after getting the regression model? -Answer We can predict
the y value by substituting each x variable value into the regression model.
How can a categorical variable be made into binary variables? -Answer It can be made
either binary 0 or 1. When all of the binary variables are 0 this is called a reference case.
We convert it into binary variables by putting in excel as
= If(.), 1, 0
What is the difference between correlation and regression? -Answer Correlation:
descriptive stats; summary of the strength and direction of relationship
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