Terminology 08 06 2014

Question 1

Specificity

Answer 1

Characteristic of a test:

Of the pole who don’t have the disease, how many of them will have a negative test.

Specificity = TN/ (TN + FP)

SP - IN

Question 2

Sensitivity

Answer 2

Characteristic of a test:

How many people with the disease with have a positive test.

Sensitivity = TP/ (TP + FN)

SN- OUT

Question 3

Predictive Value

Answer 3

probability of a disease given the results of a test.

Question 4

Positive predictive value

Answer 4

probability of a disease in a patient with a (+) test (abnormal)

PV = number of people with the disease/ number of people who have a positive test

Question 5

Negative predictive value

Answer 5

probability of not having the disease when the test value is negative.

= (# of ppl w/o disease that tested neg) divided by (# of people with negative test)

Question 6

What is a likelihood ratio?

Answer 6

it expresses how many more times (or less times) likely a test result is to be found in diseased vs. non-diseased.

Question 7

Positive likelihood ratio

Answer 7

= ratio of the proportion of diseased people with a + result
divided by
proportion of non-diseased with a positive result.

= (Sensitivity)/ (1- specificity)

Question 8

Negative likelihood ration

Answer 8

= proportion of diseased people with a (-) test
divided by
proportion of non-diseased with (-) test

Question 9

Risk Reduction

Answer 9

= ARR/ event rate

Event rate = (a/a+c)

accounts for the effectiveness of proposed treatment and relative likelihood of an incident occur in gin the absence of treatment.

Question 10

case-control study

Answer 10

observational and retrospective

compares a group of people with disease to group without disease.

Looks for prior exposure or risk factor

measures odds ration (OR)

used to help look at rare diseases

Patient with disease is matched to a patient without disease

Question 11

cohort study

Answer 11

observational, prospective, or retrospective

compares a group with a given exposure or risk factor to a group without that exposure.

Looks to see if exposure increases the likelihood of disease.

measures Relative risk: event rate of exposed/ event rate of non-exposed.

Question 12

cross-sectional study

Answer 12

observational

Collects data from a group of people to asses frequency of disease at a particular point in time.

measures Disease prevalence – can show risk factor for association with disease BUT does not establish causality

Question 13

Twin concordance study

Answer 13

compares frequency with which both monozygotic twins or both dizygotic twins develop the same disease.

Measures heritability

Question 14

Adoption study

Answer 14

compares siblings raised by biological vs. adoptive parents.

Measures heritability and influence of environmental factors.

Question 15

Clinical trials

Answer 15

phase 0–
pre-phase I: patients take a small dose of
drug to see if you are hitting targets of drug.
- drug needs to have a wide therapeutic
windows
- target must be known.
- amount of drug given do not have any
therapeutic value.

phase 1
Small number of healthy volunteers, people
with disease. Asses toxicity and
pharmacokinetics.

phase 2
Small number of patients w/disease
- asses efficacy and optimal dosing and
adverse effects.

phase 3
Large number of patients randomly assigned
either to the treatment under investigation or
the best available placebo.
-Compares new treatment.

phase 4
Post market survellience : detects rare or long term adverse effects

Question 16

incidence

Answer 16

of NEW cases in a specific period of time/ population at risk during that same period.

Question 17

prevalence

Answer 17

of existing cases/ population at risk.

Question 18

odds ratio

Answer 18

used in Case-control studies

odds that a group with the disease was exposed to a risk factor/ odds that group without disease was exposed

(TP)(TN)/ (FP)(FN)

Question 19

relative risk

Answer 19

Cohort studies

Risk of developing disease in exposed group/ risk in unexposed group.

a/(a+c) / c/ (c+d)

Question 20

attributed risk

Answer 20

the difference in risk between exposed and unexposed groups.

Question 21

number needed to treat

Answer 21

number of patients who need to be treated to prevent 1 bad outcome.

Question 22

number needed to harm

Answer 22

number of patients who need to be exposed to a risk factor for 1 patient to be harmed.

Question 23

selection bias

Answer 23

nonrandom assignment to participation in a study group

Question 24

recall bias

Answer 24

knowledge of presence of disorder alters recall by subjects

• common in retrospective studies

Question 25

sampling bias

Answer 25

subjects are not representative of vernal population.

• results cannot be generalized to the public.
• a type of selection bias

Question 26

late-look bias

Answer 26

information gathered at an inappropriate time.

• ex. using a survey to study a fatal disease
  
  • only patients who are still alive can answer

Question 27

procedure bias

Answer 27

subjects in different groups are not treated the same.

• more attention is paid to treatment group

Question 28

confounding bias

Answer 28

when a factor is related to both exposure and outcome BUT is not in the causal pathway.

-factor distorts or confuses effect of exposure on outcome.

Question 29

lead-time bias

Answer 29

early detection confused with an increase in survival

Question 30

observer-expectancy effect

Answer 30

occurs when a researcher’s believe in the efficacy of a treatment changes the outcome of that treatment.

Question 31

Hawthorne effect

Answer 31

group being studied changes its behavior owing to the knowledge of being studied

Question 32

Meta-analysis

Answer 32

pools data and integrates result from several similar studies to reach an overall conclusion and increase statistical power.

Limited by qua lit of individual studies or bias in study selection.