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Main Deck Step 2 Content Review > Biostatistics > Flashcards

Biostatistics Flashcards

1
Q

standard deviation normal distribution a 68%

A

SD a 1 from the mean

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2
Q

standard deviation normal distribution a 95%

A

SD a 2 from mean

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3
Q

standard deviation normal distribution a 99,7%

A

SD a 3 from the mean

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4
Q

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

A

210-250

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5
Q

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

A

any rx which prolongs life

good quality of care

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6
Q

Quid of PPV(2)

A

positive predictive value

pobability of having the disease if the result test is positive

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7
Q

quid of negative predictive value

A

probability of having the disease if the test is negative

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8
Q

quid of null hypothesis

A

no relationship between exposure and outcome

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9
Q

example of null hypothesis

A

CRP high and colon cancer ,no relationship

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10
Q

what to consider when evaluating the effectiveness of new trial drug

A

the natural history of the disease

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11
Q

example drug effectiveness and drug trial(2)

A

effectiveness of antiviral drug and flu

no exact conclusion can be drawn becausecommon cold is a self limited disease

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12
Q

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

A

control arm

rx arm

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13
Q

quid of hazard ratio <1

A

the event will occur in the control arm

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14
Q

quid of hazard ratio > 1

A

the event will occur in the rx arm

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15
Q

practice of hazard ratio

A

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

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16
Q

interpretation of hazard ration close to one

A

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

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17
Q

what information is critical to successfull randomization

A

baseline characteristics

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18
Q

what an ideal randomisation

A

process to minimize selection biais and achieves possibility of cofounding variables

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19
Q

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?

A

to eliminate confounder

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20
Q

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

A

stratified analysis

modeling

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21
Q

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

A

matching
restriction
randomization

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22
Q

clue for randomization(2)

A

Rx group

Placebo group

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23
Q

when using randomization

A

during clinical trials

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24
Q

quid of restriction

A

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

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25
Q

problem with restriction

A

you cannot generalize your finding in the population

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26
Q

when using matching

A

control studies

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27
Q

importance in using macthing(2)

A

when you want to study risk factor(

exposure and outcome

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28
Q

practice of macthing

A

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

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29
Q

quid of false negative

A

the test is negative but you have the disease

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30
Q

consequence of raising the cut off value

A

false negative will increase

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31
Q

quid of precision

A

measure of random error in study

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32
Q

how to know a study is precise

A

when the confidence interval is tighter

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33
Q

what to do to increase precision of a study

A

increase the sample

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34
Q

objectif in using confidence interval

A

to measeure precision of a study

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35
Q

hazard ratio quid

A

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

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36
Q

hazard ratio less than 1

A

event less likely to occur in the rx group

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37
Q

hazard ratio more than 1

A

event likely to occur in the rx group

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38
Q

in the USMLE when hazard ration is used

A

to determine the complication of a rx

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39
Q

quid a factorial design

A

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

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40
Q

use of scatter plots

A

to demonstrate linear and non linaear patterns

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41
Q

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

A

lead time biais

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42
Q

lead time biais?

A

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

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43
Q

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

A

risk relatif RR

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44
Q

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

A

1

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45
Q

quid of relative risk

A

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

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46
Q

quid of RR>1

A

the event occurs more frequently in the exposed group

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47
Q

quid of RR< 1

A

the event occurs more frequently in the exposed group

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48
Q

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

A

two sample test

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49
Q

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

A

it’s a rare disease

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50
Q

best way to compare 3 or more means

A

two sample Z test

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51
Q

all the time RR=OR what to conclude

A

you are dealing with a rare disease

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52
Q

quid of correlation coefficient

A

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

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53
Q

what coefficient correclaition doesn’t not imply

A

causality

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54
Q

Math of CC

A

iiii

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55
Q

quid of NPV

A

proportion de personne negatif for a test reellement non malade

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56
Q

quid of PPV

A

proportion de personne positif pour un test et reellement malade

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57
Q

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

A

PPV will increase

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58
Q

quid of outlier(2)

A

an extreme and unusual value observed in a dataset

may be caused by error or mistake

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59
Q

what’s extremely sensitive to outlier

A

the mean

60
Q

what’s extremely resistant to outlier

A

mode and median

61
Q

quid of sensitivity

A

true positive/true positive+false negative

62
Q

importance of sensitivity

A

a negative test rules out the disease

63
Q

quid of specificity

A

True negative/true negative+false positive

64
Q

importance of specificity

A

positive result rule in the disease

65
Q

quid of screening test

A

test tres sensible

66
Q

quid of confirmatory test

A

test est tres specifique

67
Q

confounder

A

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

68
Q

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

A

confounder

69
Q

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

A

effect modification

70
Q

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

A

Increases the risk of ca of breast++++

no cancer

71
Q

confounding (2)

A

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
Q

effect modification(2)

A

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
Q

quid of confounder

A

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

74
Q

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

A

low

75
Q

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

A

High

76
Q

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

A

randomisation is succesful

77
Q

benefit of efrenzia over clopidogrel

A

decreased the risk of reccurent MI

78
Q

concept of number needed to be treat

A

NNT=1/absolute risk reduction

79
Q

quid of absolute risk reduction

A

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

80
Q

quid of case control study

A

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

81
Q

mean used to measure case control studies

A

odd exposure ration

82
Q

case control study ?(2)

A

you look the outcome first(the disease)

and then yo go studying the risk factor

83
Q

retrospective cohort study(2)

A

you look the risk factor first

and then you go studying the risk factor retrospectively

84
Q

goal of case study

A

asess frequency of risk factor

85
Q

goal of retrospective cohort study

A

compared incidence of disease

86
Q

goal of prospective cohort study

A

compared incidence of disease in the future

87
Q

how to measure prevalence of a disease

A

cross sectionnal studies

88
Q

how to compare outcome of interest

A

clinical trials

89
Q

prevalence

A

total number of cases in a particular point of time

90
Q

quid of P value

A

probability of abtaining a result by chance

91
Q

quid of P value

A

probability of abtaining a result by chance alone

92
Q

quid P=0,01

A

1% pobability that the resulted is obtained by chance

93
Q

P value for a test to be considered statiscally significant

A

< 0,05 or Less than 5%

94
Q

quid of susceptibility biais

A

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
Q

best way to measure incidence of a disease

A

cohort studies

96
Q

name the 2 cohort studies (2)

A

prospective

retrospective

97
Q

what calculation of incidence disease allows us to do

A

to know the relative risk

98
Q

calculation of attributable risk factor ARR

A

RR-1/RR

99
Q

quid of ARR

A

it’s a percentage

100
Q

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

A

ARR

101
Q

quid of attrition biais

A

people are loss in follow up during study

102
Q

appartenance of attrition biais

A

selection biais

103
Q

quid of hawthorne effect

A

population studied change behavior because thye are aware of being studied

104
Q

quid of generazibility of external validity

A

applicability of a result to an other population

105
Q

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

A

you can generalize the study

106
Q

clue for sectionnal study(2)

A

you assess the exposure and the outcome at the same time

snapshot study

107
Q

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

A

PPV will increase

108
Q

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

A

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

109
Q

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

A

specicicity will increase

110
Q

importance of interval de confiance (3)

A

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

111
Q

median of dataset

A

the number that divides the left side from the right side

112
Q

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

A

10/20=0,5

50% probability of having coronary disease with high CRP

113
Q

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

A

test is not reliable

114
Q

null hypothesis of a study

A

no relationship between exposure end outcome

115
Q

null value of relative risk also called confidence value

A

1

116
Q

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

A

<0,05

117
Q

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

A

<0,01

118
Q

if you have CI 0,91-1,2

A

you say the null value is inside the confidence interval

119
Q

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

A

P> ou egal a 0,05

120
Q

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

A

P.> ou egal 0,01

121
Q

example of hazard ratio

A

comparing the probability of having an adverse effect from two drugs

122
Q

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

A

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

123
Q

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

A

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

124
Q

quid of null value in RR

A

1

125
Q

importance of coefficient correlation

A

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

126
Q

example of coefficient correlation(3)

A

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
Q

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

A

1-negative predictive value

128
Q

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)

A

latency period

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

129
Q

quid of ROC curve(4)

A

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
Q

quid of attrition biais

A

it’s a selection biais

131
Q

when attrition biais is demonstrated

A

when patient is lost in follow up during a study

132
Q

observer biais

A

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

133
Q

clue for chi square

A

to calculate proportions

134
Q

representation of chisquare

A

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

135
Q

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

A

you increase the specificity

the FN

136
Q

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

A

sensitivity will increae
FP will increase
decrease positive predictive value

137
Q

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

A

confounder

138
Q

quid of founder(2)

A

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

139
Q

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

A

case control studies

140
Q

positive predictive value

A

TP/TP+FP

141
Q

negative predictive value

A

TN/TN+FN

142
Q

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

A

HIGH

143
Q

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

A

Low

144
Q

example of cross section studies

A

you measure simultaneously the the exposure and outcome

145
Q

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

A

cross sectionnal studies

Main Deck Step 2 Content Review (24 decks)

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