Evidence Based Medicine

Question 1

how can you decrease lead time bias associated with a screening test?

Answer 1

By using age specific mortality rather than survival time from diagnosis. Survival time may start looking at the studied individual even before they show clinical signs

Lead time bias is when a disease is detected by a screening or surveillance test at an earlier time point than it would have been if it had been diagnosed by its clinical appearance

Question 2

what p value indicates statistical significance

Answer 2

P value < 0.05 means that we could expect to see these results by chance alone only 5% or less of the time. i.e. 5% chance that the conclusion is mistaken

Question 3

type I error in a study is when

Answer 3

a difference between two groups is found when there isn’t one. So the lower the P value the less likely a type I error

Question 4

Type II error in a study occurs

Answer 4

when the study fails to show a difference between two groups when there is one.

Question 5

Are Cohort or Case Control studies usually prospective

Answer 5

Cohort

Question 6

what type of study starts with individuals who already have or don’t have the outcome being studies

Answer 6

Case control study

Question 7

What does Cross-sectional studies generally look for?

Answer 7

Cross sectional studies are used primarily to determine the prevalence of a problem

study/measure the outcome of the exposure at the exact same time. Ex 100 people with lung CA and 100 people without lung CA

Question 8

if a serious illness has a test to identify it, would you want high sensitivity or high specificity

Answer 8

Sensitivity.

Question 9

T/F As sensitivity goes up, specificity by definition goes down

Answer 9

T

Question 10

What type of testing is done for newborn screening

Answer 10

Tandem mass spectrometry- over 50 conditions from heel stick test Hearing

Question 11

Define positive predictive value

Answer 11

Positive predictive value is the probability that a person who receives a positive test result actually has the disease.

Question 12

What is the major difference between Sensitivity/specificity and PPV/NPV

Answer 12

S/S is fixed and defines characteristics of the test
PPV/NPV varies depending on the prevalence of the disease in the group being tested.

Question 13

Describe the difference between Sensitivity and PPV

Answer 13

Positive predictive value will tell you the odds of you having a disease if you have a positive result. … On the other hand, the sensitivity of a test is defined as the proportion of people with the disease who will have a positive result.

Question 14

What is Odds ration

Answer 14

The OR represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure. Odds ratios are most commonly used in case-control studies

Question 15

Prevalence mainly effects …

Answer 15

PPV

Question 16

95% Specificity for x means…

Answer 16

the test correctly identifies 95% of those who do not have x

Question 17

A test has 98% sensitivity means…

Answer 17

it correctly identifies 98% of those who have the disease

Question 18

define case control study

Answer 18

A case–control study is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute.

Question 19

define cross sectional study

Answer 19

In medical research, social science, and biology, a cross-sectional study is a type of observational study that analyzes data from a population, or a representative subset, at a specific point in time

Question 20

What is a strong positive likelihood ratio

Answer 20

A relatively high likelihood ratio of 10 or greater will result in a large and significant increase in the probability of a disease, given a positive test. A LR of 5 will moderately increase the probability of a disease, given a positive test. A LR of 2 only increases the probability a small amount.

Question 21

What is a strong negative likelihood ration

Answer 21

a -LR of 0.1 would indicate a 10-fold decrease in the odds of having a condition in a patient with a negative test result.