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UWorld > Biostatistics > Flashcards

Biostatistics Flashcards

1
Q

What P value is considered statistically significant?

A

P < 0.05

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2
Q

Define accumulation effect

A

Exposture to risk factor/risk reducers may depend on duration and intensity of exposure
(Therefore there may be discrepancy between patients exposed for longer period of time than those exposed less)

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3
Q

In a positively skewed distribution, there is an increased number of observations with _____ (larger or smaller) than expected magnitudes that shift the mean toward the _____ and a longer slope (tail) of the curve to the _____

A

Larger
Right
Right (positive side of distribution)

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4
Q

A negatively skewed distribution has an increased number of observations with ____ (larger or smaller) than expected magnitudes that shifts the _____ toward the left, producing a longer slope of the curve (tail) on the negative side of distribution

A

Smaller

Mean

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5
Q

In general, in a positively skewed distribution the ___ is shifted the most in the positive direction, then the ____ and then the _____
(Mode, median, mean)

A

Mean
Median
Mode

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6
Q

In a positively skewed distribution, the mean is the most shifted in the positive direction. In such a situation, the ____ is often a better reflection of the central tendency than the mean.

A

Median

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7
Q

Case control study is an observational study in which potential participans are initially identified as cases or controls based on ____

A

Disease status

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8
Q

Are case control studies retrospective or prospective

A

Retrospective

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9
Q

Case control studies compare what between groups

A

Risk factor frequency

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10
Q

The anaylsis of variance (ANOVA) test compares the ____ of how many groups

A

Means

3 or more

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11
Q

The analysis of variance (ANOVA) test requires a ____ dependent variable

A

Quantitative

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12
Q

The analysis of variance (ANOVA) test requires a ______ independent variable

A

Categorical

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13
Q

What is an independent variable?

A

What is used to divide the study pool into groups

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14
Q

What is the dependent variable

A

The outcome

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15
Q

If a patient asks “what are the chances that I really do not have thyroid cancer?” After receiving results on a biopsy saying a nodule was benign, what diagnostic test parameter would be most helpful for answering their question

A

Negative predictive value

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16
Q

How is negative predictive value calculated

A

True negatives divided by total number of negative tests

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17
Q

Does negative predictive value vary with the prevalence of disease in the target population?

A

Yes

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18
Q

What is a type I error

A

Rejecting a true null hypothesis

Determining there is a correlation when one truly does not exist

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19
Q

What is a type II error

A

Fail to reject false null hypothesis

Determine there is no correlation when one truly exists

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20
Q

What is the power of a test?

A

The probability of making the correct decision of rejecting a false null hypothesis

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21
Q

What is the probability of a type II eror

A

The probability of failing to reject a false null hypothesis

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22
Q

How can the power of a test be calculated from the probability of a type II error

A

Power = 1 - (probability of a type II error)

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23
Q

What is the p-value

A

The probabililty of obtaining the observed result when the null hypothesis is assumed to be true
(Informally interpreted as the probability that the observed results are due to chance)

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24
Q

What is pretest probability

A

The probability of having the disease before testing

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25
Q

A t-test compares the ____ of how many groups

A

Mean

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26
Q

A t-test requires a ___ dependent variable and ___ independent variable

A

Quantitative

Categorical

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27
Q

How does a t-test differ from a paired t-test

A

T-test: 2 groups are independent
Paired: matched groups are formed (either same individuals being assessed twice or individuals are matched with indivduals in the other group based on certain attributes)

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28
Q

Does phase I testing in a clinical trial include healthy or ill patients

A

Healthy

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29
Q

Does phase II testing include healthy or affected subjects

A

Affected

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30
Q

What phase study asses the safety, pharmacokinetic profile, and metabolism of a drug in a smal number of healthy subjects

A

Phase I

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31
Q

What is the goal of phase III clinical trials

A

Assess safety and effectiveness of a new treatment compared to a standard treatment or a placebo

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32
Q

Expansive populations have ____ birth rates and ____ mortalilty rates

A

High

High

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33
Q

Expansive populations have ___ life expectancy and a _____ population

A

Short

Growing

34
Q

Stationary popilations have a ___ in birth rates and ___ mortality rates

A

Decline

Low

35
Q

Stationary populations have a ____ life expectancy and ____ population

A

Long

Stable

36
Q

Constrictive populations have ____ birth rates and ___ mortality rates

A

Very low

Low

37
Q

Constrictive populations have ___ life expectancy and a ___ population

A

Long

Shrinking

38
Q

What type of population would be expected in a very advanced country with a high level of lilteracy, easy access to birth control mesures, and exceptional health and medical resources? (Constrictive, stationary, or expansive)

A

Constrictive

39
Q

What population type is seen in many developed countries (stable, expansive, or constrictive)

A

Stable

40
Q

what is the equation for positive predictive value

A

true positive / (true positive + false positive)

41
Q

how can you calculate the true negatives with the sensitivity

A

true negatives = sensitivity x patients without disease

42
Q

what is the attack rate?

A

number of people who contracted an illness divided by people who are at risk of contracting that illness

43
Q

matching is a method often used in case control studies to control what bias?

A

confounding

44
Q

according to, Hardy weinberg analysis, what variables represent disease frequency

A

q squared

45
Q

according to Hardy weinberg analysis, how is carrier frequency represented for recessive disorders

A

2q

46
Q

what is the purpose of randomization

A

to make experimental groups as similar as possible

47
Q

what test is adequate for qualitative dependent variable and qualitative independent variable

A

chi-square

logistic regression

48
Q

what test is adequate for qualitative dependent variable and quantitative independent variable

A

logistic regression

49
Q

what test is adequate for a quantitative dependent variable and qualitative independent variable

A

t-test
ANOVA
linear regression

50
Q

what test is adequate for a quantitative dependent variable and quantitative independent variable

A

correlation

linear regression

51
Q

which would you likely calculate an odds ration: in a cohort study or case-control study

A

case-control

52
Q

which would you likely calculate relative risk: in a cohort study or case control study?

A

cohort study

53
Q

In a null hypothesis for a case control study, the odds ration will be equal to ___

A

1

54
Q

what is the power of a study

A

power = 1 - (probability there is no difference in the two groups, or that the null hypothesis is correct)

55
Q

what is health promotion

A

the process of enabling people to increase control over their health and its determinants, and thereby improve their health (it is a form of primary intervention)

56
Q

how does a larger population affect negative and positive predictive values

A

increases positive predictive value

decreases negative predictive value

57
Q

what is a statistical method commonly employed to compare the means of 2 groups of subjects

A

two-sample t test

58
Q

what type of bias includes error due to loss to follow up

A

selection bias

59
Q

what percentage of observations lie within 1, 2, and 3 standard deviations of the mean?

A

1: 68
2: 95
3: 99.7

60
Q

what is effect modification

A

when the effect of the main exposure on the outcome is modified by the presence of another variable (not a bias, not the same as confounding)

61
Q

what is alpha?

A

the significance level used to establish the statistical significance of s study result, a study is considered statistically significant when the p value is less than the significance level (alpha)
alpha is also the probability of making a type 1 error

62
Q

what does “r” stand for in biostatistical analysis

A

correlation coefficient, the direction and strength of a linear relationship between 2 variables

63
Q

what p value represents statistically significant data

A

less than the significance level

64
Q

what 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 perioed

A

case series

65
Q

what phase trial assesses treatment efficacy, toxicity, adverse effects, and optimal dosing strategies in a small number of affected subjects

A

phase II

66
Q

what is attributable risk percent

A

the excess risk in the exposed population that can be attributed to the risk factor
ARP = [(RR-1)/RR]

67
Q

What is statistical power in a biostatistical study?

A

a study’s ability to detect a difference when on exists

1-beta

68
Q

what statistical test evaluates association between 2 categorical variables

A

chi square test

69
Q

how can absolute risk reduction be calculate

A

event rate in control - event rate in treatment group

70
Q

how does a confidence interval determine if a relevant risk is significant or not

A

if a confidence interval contains the relative risk value, it is not statistically significant
ie. CI of .57-1.28 and RR =.87 indicates not statistically significant

71
Q

define precision vs accuracy

A

precision: ability of test to reproduce identical or similar results with repeated measurements (ie. hitting the same spot on a dart board repeatidly)
accuracy: validity, ability of test to measure what it its actually supposed to measure (ie. getting a bulls eye)

72
Q

How should non compliant test subject’s data be treated in a study that uses “intention-to-treat”

A

included regardless of their compliance

73
Q

how is number needed to harm interpreted between 2 treatment options

A

NNH = 1/ absolute risk increase

74
Q

if the parameter of interest is a difference between groups, what confidence interval will indicate statistically significant

A

if the confidence interval does not include the null hypothesis, which is 0 when testing for a difference between groups, the data is statistically significant
(if comparing relative risk or odds ration, the null value is 1)

75
Q

how is the confidence interval of the mean calculated

A

confidence interval of mean = mean + [z-score for confidence leve] x (SD/square root of n)

76
Q

which of the follow has the best indication of accuracy: sensitivity, specificity, area under the curve

A

area under the curve

closer to 1 = more accurate

77
Q

what do you know about the p value if the 95% confidence interval does not include the null hypothesis

A

the p value is < .05

78
Q

what is length time bias

A

subjects with a rapidly progressive form of disease are less likely to be detected by screening compared to those with slowly progressive disease

79
Q

what phase of a drug trial includes post marketing surveillance that assesses rare or delayed adverse effects of newly approved treatments on the market

A

phase IV

80
Q

The unit of analysis in ____ studies is populations rather than individuals

A

ecological

81
Q

what is the equation to determine relative risk reduction

A

RRR= (Risk in control- risk in treatment)/risk in control

or

RRR= 1-relative risk

UWorld (19 decks)

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