Exam #1: Biostatistics IV Flashcards
How can two qualitative variables be described?
1) Cross-tab table
2) Cluster bar graph
3) Numerically
What is an odds ratio?
A summary of the cross-tab table in a single number
How is an odds ratio calculated?
AD/BC
What is necessary to calculate an odds ratio?
Must have binary variables
How can the relationship between one qualitative and one quantitative variable be represented?
1) Tabular
2) Graphically
What does the box in a box and whisker plot show?
Spread of variables
What does the heavy line in a box and whisker plot show?
Median
What do vertical lines/whisker in a box and whisker plot show?
- Upper quartile
- Lower quartile
How are outliers shown on a box and whisker plot?
Graphed independently
What is a spearman rank-order correlation coefficient?
Summarizes the relationship between to ordinal scale variables
What is the symbol for a spearman rank-order correlation coefficient?
Rs
What is the range of possible Rs values? What do they mean?
-1 to 1
1= strong positive relationship
- one value up, other up
- 1= strong negative relationship
- one value up, other down
0= no relationship
What is does the p-value translate into?
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
How can the relationship between two quantitative variable be shown?
1) Graph
2) Scatter-plot
What does a zero correlation mean?
No linear pattern between two factors
What does a perfect correlation mean?
Each data point falls exactly on a straight line
What is a regression line?
Best fitting straight line to a set of data points
**Minimizes the distance of all data points that fall from it
What is the pearson correlation coefficient?
A measure of the direction and strength of a linear relationship
What is covariance?
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
What is a regression analysis?
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
What is y on a graph in statistics?
Dependent variable
What is x on a graph in statistics?
Independent variable
**This is the variable that we think it the CAUSE
When do you use a logistic regression?
When y,or the independent variable, is qualitative
