# Quiz in Stata

** ****Mark all answers. There may be more than one answer for each question.**

1, Odds ratios may be calculated for

A, a cohort study

B, a prospective study

C, an experimental study

D, all of the above

E, none of the above

2, A discrete random variable

A, has no mean

B, may have only negative values

C, may have only positive values

D, all of the above

E, none of the above

3, For a standard normal random variable

A, if *P (Z<a) *<0.5, then* a *must be positive

B, *E(Z)*=0

C, *Var(Z)*=1

D, all of the above

E, none of the above

4, If P(a<X<b) ≈0.95, then which of the following are possible

A, X ~ N ()

B, X ~ B ()

C, a<0, b>0

D, all of the above

E, none of the above

5, A case-control study

A, is preferable to a clinical trail

B, samples based on the outcome of interest

C, samples based on the exposure of interest

D, all of the above

E, none of the above

6, When should classes be omitted from a frequency tables?

A, when class counts are zero for quantitative variables

B, when class counts are zero for ordinal variables

C, when class counts are zero for nominal variables

D, all of the above

E, none of the above

7, A study estimated the average heights (in inches) of males under the age of 30, to be 69.8 inches with a standard deviation of 2.5 inches. Which of the following might be the 95% CI estimate for the average heights of males under of 30?

A, (69.3, 70.3)

B, (68.8, 70.8)

C, (68.3, 71.3)

D, all of the above

E, none of the above

8, Stratified analyses

A, Should not be used for skewed data

B, May reveal differences between groups

C, Are rarely useful

D, all of the above

E, none of the above

9, For a standard normal random variable,

A, P(Z>a) = P(Z<-a)

B, 1 – P(Z>a) = P(Z>-a)

C, P(Z>a) + P(Z<a)=1

D, all of the above

E, none of the above

10, For a normal random variable, if a<b, which of the following must be true?

A, P(a<X<b) < 0.5

B, P(a<X<b) = 0.5

C, P(a<X<b) > 0.5

D, all of the above

E, none of the above

11, For a normal random variable, if P(a<X<b) < 0.5, which of the following must be true?

A, a<0, b<0

B, a>0, b>0

C, a<0, b>0

D, all of the above

E, none of the above

**Solution**** **

1, Odds ratios may be calculated for **Ans. B,C**

A, a cohort study

B, a prospective study

C, an experimental study

D, all of the above

E, none of the above

2, A discrete random variable **Ans. B,C**

A, has no mean

B, may have only negative values

C, may have only positive values

D, all of the above

E, none of the above

3, For a standard normal random variable **Ans. B,C**

A, if *P (Z<a) *<0.5, then* a *must be positive

B, *E(Z)*=0

C, *Var(Z)*=1

D, all of the above

E, none of the above

4, If P(a<X<b) ≈0.95, then which of the following are possible **Ans. A,C**

A, X ~ N (m, s)

B, X ~ B (1, 0.5)

C, a<0, b>0

D, all of the above

E, none of the above

5, A case-control study **Ans. A,B**

A, is preferable to a clinical trail

B, samples based on the outcome of interest

C, samples based on the exposure of interest

D, all of the above

E, none of the above

6, When should classes be omitted from a frequency tables? **Ans. A**

A, when class counts are zero for quantitative variables

B, when class counts are zero for ordinal variables

C, when class counts are zero for nominal variables

D, all of the above

E, none of the above

7, A study estimated the average heights (in inches) of males under the age of 30, to be 69.8 inches with a standard deviation of 2.5 inches. Which of the following might be the 95% CI estimate for the average heights of males under of 30? **Ans. A,B,C,D NOTE: Not sure about this as the sample size **

A, (69.3, 70.3) **is not given.All three options are possible.**

B, (68.8, 70.8)

C, (68.3, 71.3)

D, all of the above

E, none of the above

8, Stratified analyses **Ans. A,B,C,D**

A, Should not be used for skewed data

B, May reveal differences between groups

C, Are rarely useful

D, all of the above

E, none of the above

9, For a standard normal random variable, **Ans. A,B,C,D**

A, P(Z>a) = P(Z<-a)

B, 1 – P(Z>a) = P(Z>-a)

C, P(Z>a) + P(Z<a)=1

D, all of the above

E, none of the above

10, For a normal random variable, if a<b, which of the following must be true? **Ans. A,B,C,D**

A, P(a<X<b) < 0.5

B, P(a<X<b) = 0.5

C, P(a<X<b) > 0.5

D, all of the above

E, none of the above

11, For a normal random variable, if P(a<X<b) < 0.5, which of the following must be true? **Ans. A,B,C,D**

A, a<0, b<0

B, a>0, b>0

C, a<0, b>0

D, all of the above

E, none of the above