Statistics

Question 1

Intraindividual Variation

Answer 1

produced by conditions which cause a single individual’s laboratory values to change at different times of day or under different physiologic conditions

CHAP lives in SF
-circadian rhythms
-hydration
-activity
-stress
-posture
-food intake

Question 2

Interindividual Variation

Answer 2

reflects the many different factors which cause laboratory test results to vary from one individual to another within a population

SAD BGG
-age
-sex
-diet
-body mass
-general activity level
-genetic

Question 3

Gaussian vs non-Gaussian

Answer 3

Gaussian
-parametric method
-reference range is mean +/- 2 sd

non-Gaussian
-non parametric method
-reference range is inner 95% of defined population

Question 4

False Positives and False Negatives

Answer 4

FP = healthy labelled as diseased

FN = diseased labelled as healthy

Question 5

Sensitivity

Answer 5

-proportion of diseased subjects correctly classified by the test; i.e., the ability to detect a true positive in a person afflicted with the disease

Question 6

Specificity

Answer 6

-proportion of healthy subjects correctly classified; i.e., the ability to exclude a diagnosis in a healthy person

Question 7

Predictive Value of a Positive Test

Answer 7

The predictive value of a positive test result is the fraction of positive test results which are correct, or the true positives divided by all the positives, both true and false

Question 8

Predictive Value of a Negative Test

Answer 8

The predictive value of a negative test is the fraction of all negative results which are correct, or the true negatives divided by all the negatives, both true and false

Question 9

As the prevalence of disease increases, the predictive value of a positive test ___

Answer 9

IMPROVES

Question 10

As the prevalence of disease decreases, the predictive value of a negative test ____, and the predictive value of a positive test is ____ by increasing numbers of false positive results

Answer 10

1. IMPROVES
2. DIMINISHED

Question 11

How do you know if my therapy has changed the patient’s lab values?

Answer 11

-determine if the difference between the first and subsequent measurement is greater than 3 times the standard deviation of the assay

-if so, then you can be 95% confident that the difference between the two measurements is not due to chance

Question 12

Random Analytic Variation

Answer 12

-inevitable and all its points will fall within a Gaussian distribution

Question 13

Systemic Error

Answer 13

-occurs when some new variable is introduced, such as deterioration of a reagent, clogging of a tube within the instrument, etc
-likely to compromise the accuracy of test results
-if any result is more than 3 SD from the mean, it is interpreted as probable systematic error and treated as such