Final-lecture 12

Question 1

What are dummy variables or indicator variables?

Answer 1

-nominal level variables

Question 2

What is the only type of statistics dummy variables can be used in?

Answer 2

-multiple regression models

Question 3

What is dichotomous and polytomous?

Answer 3

• only two categories

- three or more categories

Question 4

How would sex be coded?

Answer 4

• 0 would be the reference category

- 1 would be the category of interest

Question 5

What does the coding for dichotomous dummy variables tell us?

Answer 5

-it indicates the absence or presence of a characteristic/trait

Question 6

When there are only two categories for a dummy variable, what can be determined?

Answer 6

-the extent of difference

Question 7

What is the reference group?

Answer 7

-coded as 0

Question 8

What would a response of 1 indicate if 1=female and 0=male?

Answer 8

-the person is 100% more female than a person who is male

Question 9

Can we measure the difference between dichotomous dummy variable response categories?

Answer 9

-Yes, since 0 is the reference group and 1 is the experimental group

Question 10

What should categories be when coding for dummy variables?

Answer 10

-mutually exclusive

Question 11

In SPSS, if male=1 and female=2 what would we need to do?

Answer 11

-change into 0 and 1

Question 12

Explain what the two variables are when the independent variable is a dichotomous dummy variable and how each variable relates to Y (use sex as the independent)?

Answer 12

• first variable is Y
• second is the dichotomous dummy variable which has two categories
• we ask if the mean of Y for females is different than the mean of Y for males

Question 13

If means are different between both females and males Y values, what do we need to do to determine if the mean difference is in the population?

Answer 13

• run a test of significance

- t-test

Question 14

Is it possible to observe a difference in a sample even if there isn’t a difference in the population?

Answer 14

• it is do to random chance

- sampling variability can lead to variation in sample means

Question 15

What is hypothesis testing?

Answer 15

-the likelihood we would observe a sample difference if there is no difference in the population

Question 16

What is the null hypothesis?

Answer 16

-population mean 1 is equal to population mean 2

Question 17

To test the null hypothesis for difference between groups what do we use?

Answer 17

-a t-test

Question 18

How can we control for other factors if we wanted to test sex and its impact on days of work limited by health?

Answer 18

-use multiple regression to control for other factors

Question 19

Do we control for nominal variables in the same way as interval-ratio variables?

Answer 19

-No

Question 20

What achieves the same test as a t-test of difference in means?

Answer 20

-bivariate OLS regression

Question 21

Normally, what does OLS regression examine?

Answer 21

-the mean change in Y with a one unit change in X

Question 22

What kind of statistic is the mean?

Answer 22

-least-squares statistic

Question 23

If you have two categories within your X variable (dichotomous dummy variable) what does the prediction do?

Answer 23

• the prediction minimizes the error for the first group and is the mean of Y for that group
• same thing with the second group

Question 24

What does the least squares line pass through with a dichotomous dummy independent variable?

Answer 24

-two means of each group to minimize error

Question 25

What does b become when testing a dichotomous dummy variable?

Answer 25

-the difference in group means

Question 26

What does the t-test for b become when testing a dichotomous dummy variable?

Answer 26

-the t-test for b is a test of difference in group means

Question 27

In multiple regression, what does the constant equal to?

Answer 27

-the mean of the reference category

Question 28

What is the same as the coefficient for the independent variable in bivariate regression with dummy variables?

Answer 28

• the difference in group means observed in the t-test

- i.e. mean difference

Question 29

What does a + b equal in a bivariate dichotomous regression with dummy variables, use sex with female=1?

Answer 29

-it equals the mean for females (if females are coded as 1)

Question 30

How can one standardize dummy variables?

Answer 30

• standardizing Y

- creates a semi-standardized coefficient for X that indicates differences in means of standardized outcome

Question 31

What do semi-standardized coefficients indicate?

Answer 31

-mean difference in groups in terms of standard deviations of the outcome

Question 32

What can dummy variables be used for in a multiple regression?

Answer 32

-take into account possible causes of spuriousness that affect the relationship between predictors and dependent variable

Question 33

For dummy variables, what tests do you run and in what order?

Answer 33

• first a t-test between dependent and independent

- then a regression of them if previous step was significant

Question 34

If we control for a second independent variable in our regression between a dichotomous dummy variable and dependent variable what is it equivalent to studying? For example, education and mastery and we control for age

Answer 34

• it is equivalent to examining educational differences for individuals who are at the same level of age
• constant has no meaning

Question 35

What is the most important thing to observe when researching for spuriousness when controlling for a second independent variable?

Answer 35

-the slope for the independent variable becomes non-significant in model 2