The Descriptive Analysis Flashcards
What are Frequency Tables used for?
Used to present counts and frequencies of discrete or continuous data at any level of measurement
What are the components that must be included in a frequency table?
Clear title, descriptive column names, adequate space, and row/column delineation
What are Box and Whisker Plots used for?
Used to visualize the range or spread of data
Only 1 Axis is in mathematically meaningful units
What does the Box depict?
IQR (Qu - Ql), Median, and Mean
What does the Whiskers depict?
Min and Max values
What axis is the mathematically relevant one usually in Box and Whiskers?
Y-Axis
What are Bar Charts used for?
Used to graph discrete/categorical data
What are the bar charts ideal for visualizing?
Frequencies and Distributions, but not ideal for presenting trends over time
What are the components of a bar chart that must be included?
Title labeled axes with well defined units, columns NOT touching, aligned vertical or horizontal
What are Histograms used for?
Used to graph numeric data that have been apportioned into discrete categories
What are the components of a histogram that must be included?
Columns touching, title, labeled axes with well defined units
What do histograms usually illustrate?
Changes in a variable over time
What are Class Intervals?
Summarize by grouping the data into a set of contiguous, non-overlapping intervals, such that each value in the set of observations can be placed in one, and only one, of the intervals
How many class intervals do you use?
Too few = lose information
Too many = objective of summarization will not be met
What is the common rule of thumb for class intervals?
No fewer than 6 intervals but no more than 15, intervals should be the same length
What is a Frequency Polygon?
Line graph in which we place a dot above the midpoint of each class interval and connect the dots
How does a Frequency Polygon look?
Begin and End with the line touching the X-Axis
Each group is represented with a different line
What are Pie Charts?
Used to represent proportions or relative quantities of values
What is the definition of Proportion?
The number of observations with a given characteristic divided by the total number of observations in a given group
How to calculate proportion?
Take the variable you are interested in and divide it by the total
What is the Rate?
Similar to proportion but competed over a SPECIFIC time-period and use a MULTIPLIER aka the base
What is Incidence?
Measure of Morbidity
Measures the number of new cases of a disease/symptom/problem that develops in a population risk within a given period of time
What is Prevalence?
Measure of Morbidity
Measures the probability of having a disease at a point in time
Reflects existing disease within the population
What does prevalence represent best?
Represents the best estimate of the probability of the presence of disease before evaluation and individual’s history, physical exam, or lab tests
What is POCT?
Point of Care Testing
Standard Two by Two Table Set Up
W X
Y Z
What do the variables mean in a 2 by 2 table?
W: true positive, patients with condition and tested positive
X: false positive, patients w/o condition and tested positive
Y: false negative, patients with condition and tested negative
Z: true negative, patients w/o condition and tested negative
What is the false positive rate?
Number of false positive results divided by all patients who do not have the disease
How do you calculate the false positive rate?
(X) / (X+Z)
What is the false negative rate?
Number of false negative results divided by all patients with the disease
How do you calculate the false negative rate?
(Y) / (W+Y)
What is Sensitivity?
The ability of a diagnostic test to correctly identify individuals with disease
Proportion of individuals with the disease who are correctly identified by the test
How do you calculate the sensitivity?
(W) / (W+Y)
What is sensitivity also known as?
True positive rte
High sensitivity with low false negative rates
What is Specificity?
The ability of a diagnostic test to correctly identify individuals without disease
Proportion of individuals without the disease who are correctly identified by the test as disease-free
How do you calculate the specificity?
(Z) / (X+Z)
What is specificity also known as?
True negative rate
High specificity with low false positive rates
What is the Predictive Value?
How likely it is that the individual does or does not have the disease give their test result
What is a Positive Predictive Value?
Probability that a patient has the disease given that a positive test result was obtained
How do you calculate the positive predictive value?
(W) / (W+X)
What is a Negative Predictive Value?
Probability that a patient does not have the disease given that a negative test result was obtained
How do you calculate the negative predictive value?
(Z) / (Y+Z)
What are predictive values affected by?
Prevalence of the disease in the population of interest
Ex. A research study evaluated the use of saliva tests for COVID. 60 patients with the virus confirmed by PCR were evaluated. 40 patients without the virus were also included. The saliva test results were positive in 40 pts with the virus and in 10 in the pts without the virus. How do you set up the table?
W: 40 X:10
Y: 20 Z: 30
What are ROC Curves?
Receiver Operating Characteristic Curves
What are ROC Curves used for?
To illustrate the trade-offs between sensitivity (true positive rate) and the false positive rate
What do the points on the ROC curve represent?
Each point on the ROC curve represents the sensitivity and false positive rate at a different decision thershold
What does the Y Axis represent on the ROC?
True positive rate = Sensitivity
What does the X Acid represent on the ROC?
False positive rate
What does 0,0 represent on the ROC?
Represents 0% sensitivity and 0% false positive rate, all test results are negative for disease
What does 1,1 represent on the ROC?
Both the sensitivity and false positive rates are 100%, all test results are positive for disease
What is the Chance Diagonal?
Connects 0,0 to 1,1 in a straight line
What the does the Chance Diagonal represent?
No ability to discriminate between patients with disease vs. those without disease
Where does the ROC Curve need to lie to have some diagnostic ability?
ABOVE the Chance Diagonal
What is area under the ROC?
Allows for comparisons of different diagnostic tests
What is the area under the Chance Diagonal?
0.5
What is the area under the ROC for a perfect diagnostic test?
1
