STATS Flashcards
Population
A population is the entire collection of objects or outcomes about which information is sought
Sample
A sample is a subset of a population, containing the objects or outcomes that are actually observed
Simple random sample
A simple random sample (SRS) of size n is a sample chosen by a method in which each collection of n population items is equally likely to comprise the sample
N
n is the number of values in your sample. If you measure the heights of students in a class of 27, then n = 27
Median
Median (also called the “midrange” – the middle number of the ordered set of values
– If n is odd, then the median is middle number * 1,2,4,5,6 median = 4
– If n is even, then the median is the average of values in middle position
* 2,3,4,7,9,10 median = 4+7=11/2=5.5
Mode
Mode – the most frequently occurring value in a sample
– 2,2,2,3,3,3,3,5,5,6,6 mode = 3
Range
Range – the difference between the largest
and smallest values in a sample
– 23, 33, 35, 55, 70 range is 70-23=47
Mean
the sum of the values divided by the number of values. __
– 1,3,4,5,7 sum = 20 X = 20/5 = 4
Means are not always meaningful by themselves!
Variance
how far a set of random numbers are from their mean
Standard deviation
the square root of the variance
discrete data
acountofwholeevents,objects or persons. For example, the number of people with a certain illness is a discrete quantity
Continuous data
themeasureofaquantitysuch as length, volume, or time, which can occur at any value. For example, the concentration of glucose in the blood is a continuous quantity. Even if the instrument you are using rounds off values to whole numbers, these quantities are still continuous.
Standard deviation
Expresses the degree to which each data result
tend to vary about the mean value
– SD is the square root of the variance of the sample
– SD - measures precision
– SD - used to set confidence limits upon which control result acceptability is determined
Standard deviation formula
Standard deviation formula
Range of standard deviation
Example-
Average: 90mg/dl
Normal range-
Average for population- +/- 2SD
example= glucose
Average: 90mg/dL
1SD= 10mg/dL
90 + 2SD= 110mg/dL
90- 2SD= 70mg/dL
normal range= 70-110 mg/dL
Exceptions to Range
When any value is not normal
- drug screens, disease markers, Morphology
When the test is qualitative
- HIV, throat culture, genetic testing
When monitoring response to medication
- refer to therapeutic range
Level Jennings chart
– Graphically display the assay (QC) values of replicated
controls vs. time or consecutive runs
– Confidence limits are calculated from the mean and SD. It is customary to use +/- 2 SD as the confidence limits. (95% confidence limit)
Level Jennings chart
Quality control charts are
Quality control charts are used to record the results of measurements on control samples, to determine if there are systematic or random errors in the method being used.
Accuracy
The closeness to which a value comes to the true value- established by calibration
Precision
The reproducibility of a value
- evaluated by use of QC materials- evaluates the degree of fluctuation in the measurements
To be reliable
A method must be both accurate and precise
Measures of precision
– Variance
– Standard Deviation
– Coefficient of Variation – F-Test