Laboratory Statistics and Quality Control Flashcards
What is sensitivity and how is it calculated?
Probability of correctly classifying a diseased person as diseased
TRUE POSITIVE RATE
% Sensitivity = # of Diseased Persons with positive test result / Total # Diseased Persons X 100
OR
of True Positives / (# True Positives + # False Negatives) X 100
What is Specificity and how is it calculated?
Probability of correctly classifying a nondiseased person as nondiseased
TRUE NEGATIVE RATE
%Specificity = #Nondiseased Persons with negative test result / Total # Nondiseased Persons X 100
OR
True Negatives / (True Negatives + False Positives)
How is positive predictive value calculated?
True Positives / (# True Positives + # False Positives) X 100
How is negative predictive value calculated?
True Negatives / (# True Negatives + # False Negatives) X 100
What is the False Positive Rate? How is it calculated?
False Positives / Total # Nondiseased Persons X 100
Probability of incorrectly classifying a nondiseased person as diseased
OR
1 - Specificity (True Negative Rate)
What is the False Negative Rate and how is it calculated?
The probability of incorrectly classifying a diseased person as nondiseased
False Negatives / Total # Diseased Persons X 100
OR
1 - Sensitivity (True Positive Rate)
What is the difference between accuracy and precision?
Accuracy = closeness of measured value to its true value (ability to get close to bullseye)
Precision = closeness of repeated measurements of the same quantity (ability to hit the same spot on the target repeatedly)
What is a Normal Distribution?
AKA Gaussian Distribution = Normal Bell Curve
-Single peak representing mean of the population of observations
- 68.26% of observations (values) that make up distribution will fall between +/- 1 SD of the mean
- 95.46% between +/- 2 SD
-99.73% between +/- 3 SD
What are the standard deviation distributions/frequencies in a normal bell curve?
1 SD = 68.26%
2 SD = 95.46%
3 SD = 99.73%
Where is the mean in a unimodal vs skewed data set?
In unimodal/symmetrical data set, mean will be in the center of the curve
In skewed data set mean will be shifted left (negative) or right (positive) of peak of the curve
What is the Median of data set?
Divides all data points exactly in half with one half higher and one half lower than the median number
- Median is also 50th percentile
-Non parametric method (Not calculated from formula)
- Mean is parametric (from formula)
-If odd number of data points, median will be value in the middle
-with even number of data points, median is average of two middle values
What is the Mode in a dataset?
Most commonly occurring value in dataset
-not very useful measure for describing or comparing data sets
-shows when data set consists of two or more different populations that result in more than one mode
- BIMODAL = two separate populations are present in data set
- Mode always represented by highest point on a bell-shaped curve whether the data are normal or skewed!
Where are the Mean, Median and Mode found in a Gaussian curve verses a Skewed Curve?
In gaussian curve data is unimodal - Mean, Mode and Median overlap
In a skewed data set - Mean, Mode and Median will not lay on top of one another
What is the Standard Deviation and how is it calculated?
Defined as root mean square deviation of the values from their mean or as square root of the variance
Numerical value used to indicate how widely individuals or points in a group vary from the mean of the group.
How does the formula used for Standard Deviation vary depending on the population?
If the data set is a POPULATION of its own, divide by the number of data points, N
If data set is a SAMPLE from larger population, divide by one fewer than the number of data points in the sample, n-1
Sample deviation is more common calculation in statistical analysis
What is the Coefficient of Variation? How is it calculated?
CV is the ratio of the standard deviation to its arithmetic mean
CV = (SD/MEAN) X 100
What is a Confidence Interval?
Estimated range of values which is calculated from the mean and standard deviation
Estimates statistical probability of values falling above or below the mean value on a normal bell=shaped Gaussian curve
1 SD : 68%
2 SD : 95%
3 SD : 99%
What is the Student’s T-Test?
T-Test is often used to determine how significant the differences between two groups are.
-Could the differences have occurred by chance?
-used statistically to compare group means
What is the t-score and its significance?
Ratio of difference between two groups and difference within the groups
-Larger t-score, the greater difference between the groups
-smaller t-score, the more similarity between the groups
- a t-score of 3 means groups are THREE TIMES as DIFFERENT FROM EACH OTHER as they are within each other
- When you run t-test, the bigger the t-value, there likely it is that the results are repeatable
- Large t-score tells you the groups are different, while small t-score suggests the groups are similar
What does a large t-score vs small t-score tell you?
Large t-score suggest that the groups being compared are different from each other
Small t-score shows that the groups are more similar
What are the 3 main types of t-test?
1) Independent samples t-test: compares the means for two groups. most common
2) Paired sample t-test: compares means from the same group at different times. AKA correlated pairs t-test, paired samples t-test or dependent samples t-test) Dependent samples are connected (tests on same person or thing)
3) One sample t-test : tests the mean of a single group against a known mean
