Exam #1: Biostatistics IV

Question 1

How can two qualitative variables be described?

Answer 1

1) Cross-tab table
2) Cluster bar graph
3) Numerically

Question 2

What is an odds ratio?

Answer 2

A summary of the cross-tab table in a single number

Question 3

How is an odds ratio calculated?

Answer 3

AD/BC

Question 4

What is necessary to calculate an odds ratio?

Answer 4

Must have binary variables

Question 5

How can the relationship between one qualitative and one quantitative variable be represented?

Answer 5

1) Tabular

2) Graphically

Question 6

What does the box in a box and whisker plot show?

Answer 6

Spread of variables

Question 7

What does the heavy line in a box and whisker plot show?

Answer 7

Median

Question 8

What do vertical lines/whisker in a box and whisker plot show?

Answer 8

• Upper quartile

- Lower quartile

Question 9

How are outliers shown on a box and whisker plot?

Answer 9

Graphed independently

Question 10

What is a spearman rank-order correlation coefficient?

Answer 10

Summarizes the relationship between to ordinal scale variables

Question 11

What is the symbol for a spearman rank-order correlation coefficient?

Answer 11

Rs

Question 12

What is the range of possible Rs values? What do they mean?

Answer 12

-1 to 1

1= strong positive relationship
- one value up, other up

• 1= strong negative relationship
• one value up, other down

0= no relationship

Question 13

What is does the p-value translate into?

Answer 13

Error that you make if you accept the null hypothesis

E.g. 0.05= 5% error if you reject the null hypothesis
>0.05= greater than 5% error in rejecting the null hypothesis

Thus, if p >0.05 you FAIL TO REJECT THE NULL HYPOTHESIS

Question 14

How can the relationship between two quantitative variable be shown?

Answer 14

1) Graph

2) Scatter-plot

Question 15

What does a zero correlation mean?

Answer 15

No linear pattern between two factors

Question 16

What does a perfect correlation mean?

Answer 16

Each data point falls exactly on a straight line

Question 17

What is a regression line?

Answer 17

Best fitting straight line to a set of data points

**Minimizes the distance of all data points that fall from it

Question 18

What is the pearson correlation coefficient?

Answer 18

A measure of the direction and strength of a linear relationship

Question 19

What is covariance?

Answer 19

In the pearson correlation coefficient, the extent to which x and y values vary together

**Note that this is expressed in the numerator of the pearson correlation coefficient

Question 20

What is a regression analysis?

Answer 20

Procedure to calculate the equation of the best fitting regression line of a data set AND determine the extent to which that line can predict further values

Question 21

What is y on a graph in statistics?

Answer 21

Dependent variable

Question 22

What is x on a graph in statistics?

Answer 22

Independent variable

**This is the variable that we think it the CAUSE

Question 23

When do you use a logistic regression?

Answer 23

When y,or the independent variable, is qualitative