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Flashcards in biostatistique Deck (145):
1

standard deviation normal distribution a 68%

SD a 1 from the mean

2

standard deviation normal distribution a 95%

SD a 2 from mean

3

standard deviation normal distribution a 99,7%

SD a 3 from the mean

4

example mean a 230 mg/dl pour le cholesterol and SD a 10,what's the value for cholesterol if observations are 95%

210-250

5

disease with increasing prevalence and stable incidence what happened(2)

any rx which prolongs life
good quality of care

6

Quid of PPV(2)

positive predictive value
pobability of having the disease if the result test is positive

7

quid of negative predictive value

probability of having the disease if the test is negative

8

quid of null hypothesis

no relationship between exposure and outcome

9

example of null hypothesis

CRP high and colon cancer ,no relationship

10

what to consider when evaluating the effectiveness of new trial drug

the natural history of the disease

11

example drug effectiveness and drug trial(2)

effectiveness of antiviral drug and flu
no exact conclusion can be drawn becausecommon cold is a self limited disease

12

in hazard ration interpretation what are the 2 key factors to consider(2)

control arm
rx arm

13

quid of hazard ratio

the event will occur in the control arm

14

quid of hazard ratio > 1

the event will occur in the rx arm

15

practice of hazard ratio

the chance for an event to occur during taking a drug for instance

16

interpretation of hazard ration close to one

no difference for an event to occur in the 2 groups rx arm and control arm

17

what information is critical to successfull randomization

baseline characteristics

18

what an ideal randomisation

process to minimize selection biais and achieves possibility of cofounding variables

19

a study is done using placebo and Rx,the assignment of the rx in teh two arm is done randomly using numbers generated by computer what randomization helps to do in ths case?

to eliminate confounder

20

what methods are used to eliminate cofounder during analytic stage of study

stratified analysis
modeling

21

what methods are used to eliminate cofounder during adesign stage of study(3)

matching
restriction
randomization

22

clue for randomization(2)

Rx group
Placebo group

23

when using randomization

during clinical trials

24

quid of restriction

when you limit your study to one group for example one sexe is considered

25

problem with restriction

you cannot generalize your finding in the population

26

when using matching

control studies

27

importance in using macthing(2)

when you want to study risk factor(
exposure and outcome

28

practice of macthing

you will take a group with a known risk factor and another one without it and compare

29

quid of false negative

the test is negative but you have the disease

30

consequence of raising the cut off value

false negative will increase

31

quid of precision

measure of random error in study

32

how to know a study is precise

when the confidence interval is tighter

33

what to do to increase precision of a study

increase the sample

34

objectif in using confidence interval

to measeure precision of a study

35

hazard ratio quid

ration of an event to occur in the Rx group compared to the non Rx group(arm group)

36

hazard ratio less than 1

event less likely to occur in the rx group

37

hazard ratio more than 1

event likely to occur in the rx group

38

in the USMLE when hazard ration is used

to determine the complication of a rx

39

quid a factorial design

when a study uses different interventions with two or more different variables

40

use of scatter plots

to demonstrate linear and non linaear patterns

41

any time you see a new screening test in the USMLE think of

lead time biais

42

lead time biais?

apparent survival in patients to whom a screening test is applied without changing the prognosis of the disease

43

way to interpret strengh of association and dose response relationship from a study

risk relatif RR

44

quid of null value of RR if you have null value outside

1

45

quid of relative risk

the probability for en event to occur in the exposed group compared to the probability in the non exposed group

46

quid of RR>1

the event occurs more frequently in the exposed group

47

quid of RR

the event occurs more frequently in the exposed group

48

what's the best way to to compare the mean of 2 groups of subject

two sample test

49

during a case control of disease the oddd ration is 5.0,the scientist conclude that the relative risk is 5f higher for an habit what does that imply

it's a rare disease

50

best way to compare 3 or more means

two sample Z test

51

all the time RR=OR what to conclude

you are dealing with a rare disease

52

quid of correlation coefficient

helps to tell relationship between a a risk factor and an outcome

53

what coefficient correclaition doesn't not imply

causality

54

Math of CC

iiii

55

quid of NPV

proportion de personne negatif for a test reellement non malade

56

quid of PPV

proportion de personne positif pour un test et reellement malade

57

what happen to the PPV when it's applied to a population with high incidence of a disease

PPV will increase

58

quid of outlier(2)

an extreme and unusual value observed in a dataset
may be caused by error or mistake

59

what's extremely sensitive to outlier

the mean

60

what's extremely resistant to outlier

mode and median

61

quid of sensitivity

true positive/true positive+false negative

62

importance of sensitivity

a negative test rules out the disease

63

quid of specificity

True negative/true negative+false positive

64

importance of specificity

positive result rule in the disease

65

quid of screening test

test tres sensible

66

quid of confirmatory test

test est tres specifique

67

confounder

biais that can result when the exposure disease relationship is mixed with the effect of extraneous factor

68

a crude analysis wants to see relation ship between ca of liver and smoking
stratified analysis divides the smoker in two groups one wo drinks alcohol and another who drinks alcohol but no smoker
all the ca of liver were linked to alcohol

confounder

69

when 2 factors are combined and increases the risk for a disease

effect modification

70

example of effect modification
family history of breast cancer and USE of OCP
no family history of breast cancer and USE of OCP

Increases the risk of ca of breast++++
no cancer

71

confounding (2)

two habits most of the time linked together but never cause the disease
ex:most of the time smoker also drinks alcohol but only alchohol is associated with ca of liver

72

effect modification(2)

you have an essential factor ,when combined to another one ,the risk for a disease increases +++
ex:family history of cancer and USE of OCP

73

quid of confounder

extraneous factor linked with the the expsoure and the outcome of interest

74

how will be the NPV in patient who has high probability of having a disease

low

75

how will be the NPV in patient who has low probability of having a disease

High

76

when baseline characteristis are similar in thRx group and Placebo group what does that mean

randomisation is succesful

77

benefit of efrenzia over clopidogrel

decreased the risk of reccurent MI

78

concept of number needed to be treat

NNT=1/absolute risk reduction

79

quid of absolute risk reduction

ARR=incidence with one mediction-incidence of the event winth another med

80

quid of case control study

hepls to compare people with an exposure who develops the disease from the other exposed but don't develop the disease

81

mean used to measure case control studies

odd exposure ration

82

case control study ?(2)

you look the outcome first(the disease)
and then yo go studying the risk factor

83

retrospective cohort study(2)

you look the risk factor first
and then you go studying the risk factor retrospectively

84

goal of case study

asess frequency of risk factor

85

goal of retrospective cohort study

compared incidence of disease

86

goal of prospective cohort study

compared incidence of disease in the future

87

how to measure prevalence of a disease

cross sectionnal studies

88

how to compare outcome of interest

clinical trials

89

prevalence

total number of cases in a particular point of time

90

quid of P value

probability of abtaining a result by chance

91

quid of P value

probability of abtaining a result by chance alone

92

quid P=0,01

1% pobability that the resulted is obtained by chance

93

P value for a test to be considered statiscally significant

94

quid of susceptibility biais

type of selection biais where a rx regimen is selected for a patient based on the severity the condition without taking into account other possible confounder

95

best way to measure incidence of a disease

cohort studies

96

name the 2 cohort studies (2)

prospective
retrospective

97

what calculation of incidence disease allows us to do

to know the relative risk

98

calculation of attributable risk factor ARR

RR-1/RR

99

quid of ARR

it's a percentage

100

in USMLE they will never ask what's the ARR they will say what's the percentage of colon cancer with patient with high fat diet could be attributable to their diet

ARR

101

quid of attrition biais

people are loss in follow up during study

102

appartenance of attrition biais

selection biais

103

quid of hawthorne effect

population studied change behavior because thye are aware of being studied

104

quid of generazibility of external validity

applicability of a result to an other population

105

if you study only middled age women what's the limitation of this study

you can generalize the study

106

clue for sectionnal study(2)

you assess the exposure and the outcome at the same time
snapshot study

107

using IFOBT to detect risk o colon cnacer what will happen if you increase the cutt off point in ROC curve

PPV will increase

108

what will happen when you raise the cutt point of screening test

you increase the number of criteria for the test to be positive

109

what will happen when you raise the cutt point of screening test

specicicity will increase

110

importance of interval de confiance (3)

when it's tighter
the sample size is bigger
test is more precise

111

median of dataset

the number that divides the left side from the right side

112

10 people with high CRP with cardio Vascular disease
10 people with high CRP but no vascular disease
you 20 people with CRP ,calculation 5 year cardiovascular risk

10/20=0,5
50% probability of having coronary disease with high CRP

113

you test a patient for diabete with a machine you obtain 3 results different one from another what can be said on this test

test is not reliable

114

null hypothesis of a study

no relationship between exposure end outcome

115

null value of relative risk also called confidence value

1

116

if you have confidence interval 1,2-1,5 for 95% of CI what's the value of P,null value outside the CI

117

if you have confidence interval 1,2-1,5 for 99% of CI what's the value of P

118

if you have CI 0,91-1,2

you say the null value is inside the confidence interval

119

if you have confidence interval 0,91-1,5 for 95% of CI what's the value of P Null value inside the CI

P> ou egal a 0,05

120

if you have confidence interval 0,91-1,5 for 99% of CI what's the value of P

P.> ou egal 0,01

121

example of hazard ratio

comparing the probability of having an adverse effect from two drugs

122

for a complication linkked to 2 drugs Haazard ratio =0,96 interpretation

there is no differance for the adverse reaction considering the 2 drugs because HR is closed to 0ne

123

quid of association of a strengh of a disease(3)

more a risk factro is present
more you risk to develop a disease
it's dose dependent

124

quid of null value in RR

1

125

importance of coefficient correlation

helps to determine the direction of an exposure and outcome in a linear fashion

126

example of coefficient correlation(3)

the risk with low HDL and carotid media thickness
r will be negative and P =positive
relation inverse between low HDL and carotid media thickness

127

if a test a negative what's the probability of having the disease calculation

1-negative predictive value

128

you palce a patient on statin 3 months later you assess the result ,and realise that the result is better after one year in teh prevention of CV event why?(2)

latency period
you need time to see good result when a risk modifier is used

129

quid of ROC curve(4)

x axis and y axis
extremity of both line are linked by an oblique line
space above the line is high sensitivity
space below the line is high specificity

130

quid of attrition biais

it's a selection biais

131

when attrition biais is demonstrated

when patient is lost in follow up during a study

132

observer biais

the investigator decision is adversely affectedd by knowledge of the exposure status

133

clue for chi square

to calculate proportions

134

representation of chisquare

you have a 282 table to compare expected value and oserved value

135

when you raise the cut off point consequence of that(2)

you increase the specificity
the FN

136

when you decrease the cut off point consequence of that(3)

sensitivity will increae
FP will increase
decrease positive predictive value

137

during crude analysis you found relationship between liver ca and smoke
further analysis divides the smoker in 2 groups alcoholic and non alcoholic
no association is found with liver cancer in either group
what this help us to explain

confounder

138

quid of founder(2)

extraneous factor associated with both a risk factor and outcome
most of the time alcoholic is smoker=confounder

139

when you want to determine risk factor liee a une maladie what type of study

case control studies

140

positive predictive value

TP/TP+FP

141

negative predictive value

TN/TN+FN

142

how will be the predictive positive value inside a zone with high prevalence of HIV if a screening test is used

HIGH

143

how will be the predictive negative value inside a zone with high prevalence of HIV if a screening test is used

Low

144

example of cross section studies

you measure simultaneously the the exposure and outcome

145

a group of investigator want to determine the association between 5 lipoxygenase genotype and atherosclerosis they draw blood for leucocyte genotyping and perform US to determine degree of carotid intima thickness .type of study used

cross sectionnal studies