lecture 12: screenings in medicine

Question 1

two questions you should ask when being recommended a test

Answer 1

1. how accurate is the screening test?

2. how confident will you be in your prediction of my disease state

Question 2

true positive

Answer 2

test CORRECTLY reports a POSITIVE result in a patient that actually DOES have the disease

Question 3

true negative

Answer 3

test CORRECTLY reports a NEGATIVE result in a patient that actually DOES NOT have the disease

Question 4

false positive

Answer 4

test INCORRECTLY reports a POSITIVE result in a patient that actually DOES NOT have the disease

Question 5

false negative

Answer 5

test INCORRECTLY reports a NEGATIVE result in a patient that actually DOES have the disease

Question 6

what two things answer how accurate the screening test is?

Answer 6

sensitivity and specificity

Question 7

sensitivity

Answer 7

how well a TEST can detect presence of a disease when the disease is in fact present
CALCULATING: part/whole for PRESENCE
**uses people where they already know their disease state
**tells if test gives true positive

Question 8

specificity

Answer 8

how well a TEST can detect absence of a disease when in fact the disease is ABSENT
CALCULATING: part/whole for ABSENCE
**uses people where they already know their disease state
**tells if test gives true negative

Question 9

positive predictive value (PPV)

Answer 9

how accurately a POSITIVE test PREDICTS the presence of disease
–proportion of EVERYBODY that tested positive

Question 10

negative predictive value (NPV)

Answer 10

how accurately a NEGATIVE test PREDICTS the absence of disease
–proportion of EVERYBODY that tested negative

Question 11

sensitivity calculation

Answer 11

true positive / false negative

Question 12

specificity calculation

Answer 12

true negative / false positive

Question 13

what does NOT changed based on prevalence?

Answer 13

sensitivity and specificity

Question 14

what DOES change based on prevalence?

Answer 14

PPV, NPV, false positives, and false negatives

Question 15

diagnostic accuracy

Answer 15

proportions of total screenings that a patient is correctly identified as either having disease or not having disease

TP + TN / grand total population

Question 16

likelihood ratios

Answer 16

• *ratio of TWO probabilities
• -ratio of the probability of a “given result” for a person WITH disease / ration of probability of “same result” for a person WITHOUT disease

–always WITH disease / WITHOUT disease

Question 17

likelihood ratio positive (LR+)

Answer 17

**want number to be large

probability of positive rest in PRESENCE of disease / probability of positive result in ABSENSE of disease

ALSO, sensitivity / (1-specificity)

Question 18

likelihood ratio negative (LR-)

Answer 18

**want number to be small

probability of negative result in PRESENCE of disease / probability of negative result in ABSENSE of disease

ALSO, (1-sensitivity) / specificity

Question 19

validity

Answer 19

ability to accurately discern between those that DO and those that DO NOT have disease
same as precision

Question 20

internal validity

Answer 20

extent to which results accurately reflect what was being assessed (true situation of study population)

Question 21

external validity

Answer 21

extent to which results are applicable to other populations (not included in the original study)
also known as generalizability

Question 22

reliability

Answer 22

ability of a test to give the same result on repeated uses
AKA reproducibility/consistency

**valid test is ALWAYS reliable, yet a RELIABLE test is not always valid

Question 23

multiple cutoff values

Answer 23

many diagnoses typically have two dichotomous outcomes (positive/negative); however, there could be potentially multiple cut off values that could correspond with designating presence/absense of disease

**modified to increase/decrease FP/FNs depending on disease (treatment options/risk of not being treated)