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STEP 1 > Biostats > Flashcards

Biostats Flashcards

1
Q

High sensitivity test used for ________

A

screening

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2
Q

High _______ test used for confirmation after a positive screening test

A

specificity

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3
Q

Probability that a person who has a positive test result actually has the disease

A

Positive predictive value PPV

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4
Q

Probability that a person who has a negative test result does not has the disease

A

Negative predictive value NPV

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5
Q

How does raising the Sensitivity of a test affect

Specificity

NPV

PPV

A

↑Sensitivity

↑NPV

↓specificity

↓PPV

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6
Q

How does raising the Specificity of a test affect

Sensitivity

NPV

PPV

A

↑ Specificity

↑ PPV

↓sensitivity

↓NPV

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7
Q

How does Lowering the cut off value affect

Sensitivity

FP

Specificity

FN

A
  • ↑ Sensitivity
  • ↑ FP
  • ↓ Specificity
  • ↓ FN
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8
Q

How does Raising the cut off value affect

Specificity

FN

Sensitivity

FP

A
  • ↑ Specificity
  • ↑ FN
  • ↓ Sensitivity
  • ↓ FP
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9
Q

Should Medical errors be disclosed to patients, independent of immediate outcome (harmful or not)?

A

Yes

always

Even if it is about document hand offs

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10
Q

Occurs at level of frontline operator

(ex: wrong IV pump dose programmed).

Immediate impact

A

Active Error

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11
Q

Occurs in processes indirect from operator but impacts patient care

(ex: different types of IV pumps used within the same hospital)

Accident waiting to happen

A

Latent Error

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12
Q

Adverse Event That Is Identifiable, serious, and usually preventable

(ex: scalpel retained in a surgical patient’s abdomen).

An error that never should have happened

A

Never event

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13
Q

Retrospective approach. Applied after failure event to prevent recurrence

Uses records, interviews, data

A

Root cause analysis

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14
Q

Forward-looking approach. Applied before process implementation to prevent failure occurrence.

Uses inductive reasoning to foresee what may go wrong

A

Failure mode and Effects analysis

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15
Q

Patient comfort is prioritized (positive effect) over potential side effects (negative effect).

A

Principle of double effects

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16
Q

Program is available to patients ≥65 years old,<65 with certain disabilities, and those with end-stage renal disease

A

Medicare

(Medicare for elderly)

(Medicaid for desitute)

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17
Q

Criteria to establish Decision making capacity.

(Being retarded doesn’t count as an exclusion)

A

Informed

Mentally/Mood Stable

Age is over 18

Stable decision making history

Values are consistant

Goals are consistent

Expresses a choice

(IM A SaVaGE)

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18
Q

Determined by a doctor for a specific health decision

A

Capacity

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19
Q

Determined by a Judge for any/all health decisions

A

Competency

*A competent Judge works with a Capable doctor

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20
Q

Incapacitated patient’s prior oral statements commonly used as guide. If patient was informed, directive was specific, patient made a choice, and decision was repeated over time to multiple people, then the oral directive is more valid.

A

Oral advance directive

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21
Q

Patient designates anagent to make medical decisions in the event that he/she loses decision-making capacity. Patients may also specify decisions in clinical situations. Can be revoked by the patient if decision-making capacity is intact. More flexible than a living will

A

Medical power of attoreny

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22
Q

prohibits cardiopulmonary resuscitation(CPR). Other resuscitative measures that may follow (eg,feedingtube) are also typically avoided

A

DNR order

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23
Q

What is the priority of surrogate decision makers if a patietn loses capacity without an advance directive in place

(5)

A
  1. Spouse
  2. Children (over 18)
  3. Parents
  4. Siblings
  5. relatives

SPicy CHIPS

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24
Q

List 5 exceptions to patient confidentiality

A
  • Suicidal/Homocidal patient
  • Abused or Abusive patient (kid, senior, prisoner)
  • Victims of potential harm by a patient
  • Epileptic patients need to be reported so they can’t drive (other who have impaired driving skills too)
  • Diseases like HIV, STIs, hepititis, Ebola, Food poisoning, TB need to be reported.
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25
Q

witholding information harmful to patient or that undermines decision making capacity

A

therapeutic privalege

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26
Q

List 3 things that increase in old people

A

Sleep latency (time to fall asleep)

Waking up early

suicide rate

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27
Q

Describe the 4 steps of disease prevention:

  1. Primary disease prevention
  2. Secondary disease prevention
  3. Tertiary disease prevention
  4. Quaternary disease prevention
A
  1. Prevent the disease (Vaccines)
  2. Screen for the disease (Pap smear/DRE)
  3. Treat the disease/complications
  4. Quit giving unnecessary medical treatments that can harm the patient (Imaging, polypharmy)
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28
Q

How to calculate

Case Fatality Rate

(CFR%)

A

Deaths from disease/ # People with the disease

x100

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29
Q

How to calculate

Number needed to harm

(NNH)

A

1/Attributable Risk

*Higher number = safer exposure

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30
Q

How to calculate

Number needed to treat

(NNT)

A

1/ Absolute Risk Reduction

*Lower # = Better treatment

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31
Q

How to calculate

Odds Ratio

aka: x’s more likely

A

ad/bc

* what are the odds that I was born: after death/before christ

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32
Q

How is Relative Risk calculated?

(RR)

A

if comparing 2 groups with 2 elements

(Diseased vs Healthy & Exposure vs No Exposure)

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

If comparing one group with 2 elements

(Diseased & Exposure vs No Exposure)

Exposure diseased pts/No exposure diseased pts

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33
Q

RR <1

RR =1

RR >1

A

↓ disease occurence (it’s good for you)

No association between risk/disease

↑ disease occurence (it’s bad for you)

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34
Q

The proportion of reduction of risk because of the intervention as compared to a control is called what and how is it calculated?

A

Relative Risk Reduction

RRR = 1 - Relative Risk

Relative risk = a/(a+b) / c/(c+d)

or

treated diseased pts/untreated diseased pts

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35
Q

Attributable Risk (AR)

is the difference in risk with exposed and unexposed groups.

How to calculate it?

A

a/(a+b) – c/(c+d)

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36
Q

How to calculate percent of attributable percent

(AR%)

A

(RR-1)/RR

x100

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37
Q

What is the difference in risk because of the intervention as compared to a control?

How is it calculated?

A

Absolute Risk Reduction (ARR)

c/(c+d) – a/(a+b)

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38
Q

Incidence looks at

A

New cases

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39
Q

Prevalcence looks at

A

all current cases

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40
Q

How is incidence is calculated

A

new cases/ people at risk

(per unit time)

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41
Q

How is prevalence is calculated

A

existing cases/total population

(at a POINT in time)

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42
Q

Prevalance > Incidence

In what case?

A

Chronic disease

(ex: diabetes → larger # of existing cases)

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43
Q

Prevalence = Incidence

When?

A

Short course illnesses

(Ex: the Flu)

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44
Q

How does increased survival time affect incidence & prevalence?

A

Increases prevalence only

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45
Q

How does Increased mortality affect incidence & prevalence?

A

Decreases prevalence only

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46
Q

How does Faster Recovery time affect incidence & prevalence?

A

Decreases Prevalence only

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47
Q

How does Extensive Vaccination affect incidence & prevalence?

A

Decreases

Prevalence & Incidence

48
Q

How does decreasing risk factors affect incidence & prevalence?

A

Decreases

Prevalence and Incidence

49
Q

Prevalence is increased by

A

increased survival time

50
Q

Incidence is decreased by only what 2 things?

A

Vaccination

Less Risk Factors

51
Q

What’s the difference between precision and accuracy

A

Precision: the outcomes are all consistently the same (Reliable)

Accuracy: The outcomes are all at or near the target goal (Validity)

52
Q

What decreases a test accuracy (validity)

A

Systematic error

53
Q

Bias decreases what in a test?

A

Accuracy (Validity)

54
Q

Non-random sampling or treatment allocation

A

selection bias

55
Q

participants selected from hospital only

A

Berkson Selection Bias

56
Q

participants who are lost to follow up have worse outcomes

A

Attrition selection bias

57
Q

awarness of disorder alters recall

A

recall bias

58
Q

information is gathered in a non-systematic way due to faulty procedure or equiptment

A

Measurement bias

59
Q

subjects in different groups are not treated the same or using different resources that could be the same

A

Procedure bias

60
Q

The researcher’s beliefs or desires changes the outcome or documentation of the study

A

observer expectancy bias

61
Q

An extra or hidden factor at play distorts the outcome of a study

A

Confounding bias

62
Q

Early detection is confused with increased survival

A

lead-time bias

63
Q

screening tests only effective for detecting diseases with a long latency vs those that are symptomatic earlier

have what bias?

A

Length time Bias

64
Q

Randomization can reduce what two biases?

A

Selection bias

Length time bias

65
Q

Placebos can reduce what three biases

A

Measurement

Procedure

Observer Expectancy

66
Q

Blinding can reduce what 2 bias

A

Procedure

Observer-Expectancy

67
Q

Objective, standardized, and previosuly tested methods reduce what bias

A

measurement bias

68
Q

Multiple repeated studies, cross over studies, matching in groups reduces what bias

A

confounding bias

69
Q

Measuring back-end survival

(survival according to severity)

eliminates what bias

A

lead time bias

70
Q

Define Mean, Median, Mode

A

Mean: sum of values/total values (average)

Median: Middle value (middle)

Mode: Most common value (most)

71
Q

(Standard deviation)2

A

Variance

72
Q

Mean = Mode = Median

when

A

Bell shaped curve

Normal distribution

73
Q

Mean>Median>Mode

A

Positive skewed curve

(aka left leaning)

74
Q

Mean less than Median less than Mode

A

Negatively skewed curve

(aka Right leaning curve)

75
Q

Null (H0)

means

A

no association

76
Q

Alternative (H1)

means

A

There is an association

77
Q

Stating that there is no effect or difference when none exists

A

null hypothesis not rejected

78
Q

Stating that there is an effect or difference when one exists

A

null hypothes is rejected in favor of alternative hypothesis

79
Q

Stating that there is an effect or difference when there is none

A

Alpha Type 1 error

80
Q

Stating that there is NOT an effect or difference when there is one

A

Beta Type 2 error

81
Q

If P < 0.05

what does it mean?

A

Statistically Significant

*results being by chance is less than 5%

82
Q

If P > 0.05

what does it mean?

A

Results NOT statistically significant

83
Q

Checks the differences between the means of 2 groups

A

T-test

T is meant for 2

84
Q

Checks the differences between the mean of 3 or more groups

A

ANOVA

3 words: ANalysis Of VAriance.

85
Q

Checks the differences between 2 or more percentages or proportions of categorical outcomes (not mean values).

A

Chi Squared Test

Chi-tegorical.

86
Q

Checks the differences between 2 percentages or proportions of categorical, nominal outcomes.

Use instead of chi-square test with small populations.

A

FIsher’s Exact Test

87
Q

The closer the absolute value of r is to _____, the stronger the linear correlation between the 2 variables.

A

1

*Correlation does not = causation

88
Q
  1. Positive r value =
  2. Negative r value =
  3. Co efficient of determination =
A
  1. positive correlation (as one variable ↑,the other variable ↑).
  2. negative correlation (as one variable↑, the other ↓ variable).
  3. r2 (variance in one variable can be explained by variance in another variable).
89
Q

LR+> 10 indicates

LR–<0.1 indicates

A

a highly specific test

a highly sensitive test.

90
Q

LR+> 10 =

LR–<0.1 =

A

sensitive/ 1 – specific

TP/FP

(sensitive TiP FiP)

1- sensitive/ specific

FN/TN

(specific FaN TaN )

91
Q

________ represents a study’s strength to detect a difference (ie, effect size) between treatment groups when one truly exists. It depends on _______ (among other factors).

A

Statistical power

sample size

** studies with greater sample sizes have greater power than studies with smaller sample sizes.

92
Q

Cheap fast way to calculate

TP =

FN =

A

TP = (Sensitivity) × (Number of patients with the confirmed disease)

FN = (1 − Sensitivity) × (Number of patients with the confirmed disease)

93
Q

Cumulative incidence (CI) is calculated as the total number of new cases of a disease over a specific period divided by the number of __________

A

people at risk at the beginning of the period

aka

(Total population – current cases)

94
Q

The _____ is the ratio of the number of people who contract an illness divided by the number of people who were exposed to the illness or at risk.

A

attack rate

95
Q

In a normally distributed curve

How do you calculate % of individuals 2 standard deviations away from the mean?

A

The center top of graph = MEAN

Out of a group of 100 individuals

2.35% are 2 SDs away from the mean.

*So 3 individuals (round up).

96
Q

A _______ is a descriptive observational study design in which a group of patients with a similar diagnosis or treatment is described at a point in time or followed over a certain period. This study design has no comparison group; therefore, it cannot establish associations between risk factors (eg, treatments) and outcomes (eg, diseases).

A

case series

97
Q

The power of a test is the probability of making the correct decision of rejecting a false H0 (ie determining there is a correlation when one truly exists).

If there is a 10% chance of concluding no relationship between 2 variables what is the power the study?

A

Power = 1 – ß

Power = 1 – .10 = .90

98
Q

when ____ is assumed to be true (ie not rejected) it is informally interpreted as the probability that the observed results are due to chance.

A

H0

(not rejected = results due to chance)

99
Q

A confidence interval (CI) that includes the null value for an RR (ie, RR = 1) is __________

A

not statistically significant

100
Q

A Confidence Interval, CI, that excludes the null value

(ie, RR = 1) is _______.

A

statistically significant

101
Q

Prevalence = (Incidence) x _______

A

(Duration of disease)

102
Q

The odds ratio (OR) is a measure of association used in case-control studies. It quantifies the relationship between an exposure and a disease

(ie: everyone is exposed to same hazard, but let’s compare why some got the disease and some didn’t).

its null hypothesis value is always ____

A

1

(Odds Ratio = 1).

103
Q

As disease prevalence increases, the positive predictive value _______, and the negative predictive value ________.

A

increases

decreases

104
Q

__ is the maximum probability of making a type I error that a researcher is willing to accept.

A

α

*The value of α is typically set at 0.05, meaning that researchers are willing to accept up to a 5% chance of making a type I error.

105
Q

___ is the probability of committing a type II error .Type II error occurs when researchers fail to reject the null hypothesis when it is truly false.

A

β

*if β is set at 0.2, the power will be (1 – β) = 80%; there will be an 80% chance of rejecting the null hypothesis when it is truly false (BAD).

106
Q

Case-Control compares

A

Risk Factor frequency of effects

107
Q

Cross sectional compares

A

disease prevelance

108
Q

Retrospective cohort uses past records to compare

A

disease incidence

109
Q

____ studies are organized by selecting a group of individuals, determining their exposure status, and then following them over time for development of the disease of interest.

A

Prospective cohort

110
Q

The accuracy of screening or diagnostic tests is quantified by the area under the ROC curve (AUC). The more accurate the test is (ie, higher sensitivity and specificity), the closer the AUC value is to ____.

A

1.0

111
Q

To calculate the probability of a series of independent events (ie that do not affect each other in anyway) happening all at once you must.

A

multiply their individual probabilities together

an independent event for example is a student taking a test. How one student does on the test does NOT affect how they other two students do.

IF the probability of one student a perfect score on the exam is 9% what is the probability that all 3 students will get a perfect score?

.09x.09x.09

112
Q

Quick way to calculate

True negatives =

False positives =

A

True negatives = (Specificity) * (Number of patients confirmed without the disease)

False positives = (1 − Specificity) * (Number of patients confirmed without the disease)

113
Q

Intention-to-treat analysis includes each subject in their initial randomization group even if subjects ______ or shift to a different intervention. This approach tends to provide a conservative but more valid estimate of the intervention effect in real-world scenarios (ie, clinical settings).

A

stop the intervention

114
Q

A 2 × 2 table is normally used to record the presence or absence of exposure and disease in research. Rows and columns represent the different levels for each categorical (ie, exposure and disease) variable. The chi-square test for independence is used to evaluate the association between 2 ____ variables.

A

categorical

115
Q

(adverse event rate in the control group) – (adverse event rate in the treatment group)

=

A

Absolute Risk Increase

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