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Biostatistics Flashcards

1
Q

What is continuous data? Examples

A

Logical order with values that can increase or decrease by the same amount

Examples: Ratio and IntervalW

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2
Q

What is ratio data?

A

Absolute 0 where 0 means none

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3
Q

What is interval data

A

No meaningful zero

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4
Q

What is categorical data? Examples

A

Data fits into a limited number of categories

Ex: Nominal and ordinal

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5
Q

Nominal vs ordinal data

A

Nominal: Arbitrary order (order of categories doesn’t matter)

Ordinal: Categories can be ranked

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6
Q

What is the mean? When is it preferred?

A

Average

Continuous data with a normal distribution

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7
Q

What is median? When is it preferred?

A

Number in middle with data is organized numerically

Ordinal or continuous data that is skewed

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8
Q

What is mode? When is it used?

A

Most frequently data point

Nominal data

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9
Q

What is range?

A

The difference between highest and lowest values

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10
Q

What is standard distribution?

A

How spread out data is from the mean

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11
Q

What does a large standard dev mean?

A

Large amount of data is dispersed away from the mean

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12
Q

What is another name for bell-shaped curve?

A

Gaussian

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13
Q

Where do the central tendencies lie on a Gaussian distribution

A

Mean, median, mode are the same value

68% of data falls within 1 SD of the mean

95% of data falls with 2 SD

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14
Q

What makes a distribution skewed?

A

Number of values (sample size) is small or contains outliers

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15
Q

Method of measuring central tendencies in skewed data?

A

Median

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16
Q

What is the difference between outliers of high vs low values?

A

High: Right (positive) skew → mode to median to mean (left to right)

Low: Left (negative) skew → mean to median to mode (left to right)

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17
Q

What is the difference between independent and dependent variables?

A

Independent: can be manipulated by the research

Dependent: affected by the independent variables (outcomes)

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18
Q

What is the null hypothesis?

A

That there is no statistically significant difference between groups

Researchers aim to disprove or reject

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19
Q

What is an alternative hypothesis?

A

There is a statistically significant difference between groups

Researchers aim to prove or accept

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20
Q

What is the importance for alpha

A

Maximum permissible error margin

Commonly 5%

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21
Q

How do we interpret p-value using alpha (0.05)?

A

p-value < a: reject the null proving statistical significant results (alternative hypothesis accepted)

p-value > a: accept the null stating there is no statistical significance

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22
Q

What is a confidence interval

A

Provides information on the significance of p-value

CI = 1-a

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23
Q

When would you use CI of 0 vs 1?

A

Comparing differences of means: use 0
Comparing ratio data: use 1

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24
Q

How do you interpret CI when looking at means of data?

A

CI includes 0 → Not statistically significant

CI doesn’t include 0 → Statistically significance

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25
How do you interpret CI when looking at ratio data?
CI includes 1 → Not statistically significant CI doesn't include 1 → Statistically significance
26
How do interpret a 0.95 CI 0.06, 9.35?
95% confidence that the true value lies between 6-35%
27
What is the difference between narrow and wide CI?
Narrow: high precision Wide: poor precision
28
What is a false positive? How is it represented?
The alternative hypothesis was accepted when and the null was rejected in error (Null is supposed to be accepted and no statistical significant difference present) Represented as alpha (Type 1 error)
29
What is a false negative? How is it represented?
The null was accepted and the alternative hypothesis was rejected (Alternative is supposed to be accepted → there is a statistically significant difference present) Represented by beta (Type 2 error)
30
What is power?
The probability that a test would reject the null hypothesis correctly → the avoidance of type 2 errors
31
How do you interpret power?
More power → less likely of a type 2 error to occur
32
How do you calculate risk and risk ratio?
Risk = number of subjects of an unfavorable event/Total of subjects in group Risk ratio = risk of treatment group / risk of control group
33
How do you interpret a risk ratio?
RR = 1 implies no difference in risk between the 2 groups RR > 1 implies there is a greater risk in the treatment vs control RR < 1 implies there is a greater risk in the control vs treatment
34
How to interpret a RR of .57?
The treatment group is 57% AS LIKELY to have the progression of outcomes as the control group
35
How do you calculate relative risk reduction?
RRR = (% risk of control - % risk of treatment) / % risk of control RRR = 1-RR (as a decimal)
36
How do you interpret RRR of 47%
Treatment group is 47% less likely to have the outcome than the control
37
Why is absolute risk reduction more useful than RR or RRR?
RR and RRR is comparative data between treatment and control → no meaning of absolute risk ARR includes reduction of risk and the incidence rate of outcomes
38
How do interpret a study if ARR was not reported?
Risk reduction is minimal to start with, therefore ARR would have been small
39
How do you calculate ARR?
I % of control - % of treatment I
40
How do you calculate NNT and NNH?
1/ (risk in control - risk in treatment) 1/ARR (in decimal) NNT: Round up NNH: Round down
41
How do interpret a NNT of 9 in a study that lasted for 1 yr
9 patients needed to receive treatment for 1 yr to see a progression prevented in 1 patient
42
What is NNT?
Number of patients needed to treat for a period in order to see a benefit in 1 patient
43
What is NNH?
Number of patients needed to be treated for a period in order to see one patient harmed
44
How do interpret a NNH of 9 in a study that lasted for 1 yr
9 patients needed to receive treatment for 1 yr for 1 patient to be harmed
45
What study primarily uses odds ratio?
Case control
46
What are odd ratio?
The estimated risk of an unfavorable event associated with a treatment of intervention
47
How do you calculate OR?
OR = (# outcome with exposure/ # no outcome with exposure) / (# outcome without exposure / # no outcome without exposure)
48
What data is used in survival analysis?
Hazard rate
49
How do you calculate hazard ratio
Hazard rate in treatment / Hazard rate in control
50
How do you interpret OR and HR?
OR or HR = 1: the event rate is same (no advantages to the treatment) OR or HR >1: the event in the treatment group is higher than the control group (control is more advantageous) OR or HR <1: the event is the control group is higher than treatment (treatment is more advantageous)
51
What is the difference between primary and composite endpoints?
Primary: main result that is measured for significant benefit Composite: combines individual endpoints into one measurement
52
What is the criteria of making a composite endpoint?
All endpoints must be of similar magnitude and similar importance to the patient
53
What is the difference between parametric and nonparametric test?
Parametric requires normal distribution Nonparametric: for data not normally distributed
54
Differentiate the types of t-tests? What are they for?
T-tests are used for continuous data that is normally distributed One-sample: 1 sample Dependent/paired: 1 sample (before and after) Independent/unpaired student: 2 samples (treatment and control)
55
What test is used for continuous data with a normal distribution and ≥3 samples?
Analysis of variance: ANOVA (F-test)
56
What is a sign test
Skewed distribution of 1 sample
57
What is Wilcoxon signed rank test for?
Continuous skewed distribution of 1 sample with 2 measurements Categorical data of 1 sample with 2 measurements
58
What is Mann-Whitney test used for?
Continuous Skewed distribution of 2 samples Ordinal data with 2 samples
59
What is Kruskal-Wallis test?
Continuous Skewed distribution of ≥3 samples Categorical data of ≥3 samples
60
When is chi-square tests used?
Categorical data of 1 or 2 samples
61
When is Fisher's extract used?
Categorical data of 2 samples
62
What is a correlation?
Used to determine if 1 variable changes or is related to another variable
63
What is regression?
The relationship between a dependent variable and one or more independent How the independent variable impacts or changes the dependent
64
Differentiate specificity vs sensitivity?
Sensitivity: True positive (those who test positive out of people who have the condition) Specificity: True negative (those who test negative and don't have the condition)
65
What is included in intention-to-treat?
Data from all patients are used even if patient didn't complete the trial according to the study's protocol
66
Differentiate equivalence and non-inferiority trials?
Equivalence: Demonstrate that the new treatment has the same effect as the old Non-inferiority: Demonstrate that the new treatment is no worse that the current standard
67
When are forest plots commonly used?
Meta-analysis
68
How do you interpret a forest plot?
Boxes: show the effect estimate (size of box correlates to size of study) Horizontal lines: CI represented in the trials Vertical solid line: No effect If data falls to the left of line: significant benefit If data falls to the right of the line: significant harm If CI crosses the line → results are not statistically significant Difference data: 0 Ratio data: 1
69
What is a case-control study?
Compares patients with a disease (case) to those without the disease (control) Researcher looks retrospectively of outcomes that already have happened
70
What is a cohort study?
Compares outcomes of a group of patients exposed and not exposed Researchers follow groups prospectively to see if groups develop outcomes
71
What is a cross-sectional survey?
Estimates the relationship between variables and outcomes at one particular time in a population
72
What is case report/series?
Follows a disease or ADR in a single patient (case report) or a few patients (case series)
73
What is an RCT?
Patients are randomized (having an equal chance of being in the control or treatment group)
74
How do you eliminate bias in RCT or with any study? Examples?
Blind them Double-blinded: both the patient and the investigator are unaware of treatment assignment Single-blinded: patient is unaware of treatment assignment Open-label: all parties know which treatment
75
What is the preferred study type to determine cause and effect?
RCT
76
What is a parallel RCT
Subjects are randomized to the treatment or control arm for the entire study
77
What is a crossover RCT?
Patients are randomized to one of 2 sequential treatments then switch
78
What is a factorial design?
Randomizes to more than the usual two groups to test a number of experimental conditions
79
What is meta-analysis?
Combines results from multiple studies in order to develop a conclusion that has greater statistical power
80
What is a systematic review?
Summary of the clinical literature that focuses on a specific topic or question
81
What is cost-minimization analysis?
Demonstrated equivalence in outcomes and the cost of each intervention are being compared
82
What is cost-benefit analysis?
Comparing benefits and costs of an intervention in terms of monetary units

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