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Step 3 Prep > Epidemiology/Biostats > Flashcards

Epidemiology/Biostats Flashcards

1
Q

Equation for and definition of Absoulte risk reduction (ARR)

A 
ARR = percentage indiating actual difference in event rate between control and treatment groups
ARR= Control Rate - Treatment Rate
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2
Q

Equation and definition of Relative Risk Reduction RRR

A

RRR = ARR/control rate

%indicating relative reduction in the treatment event rate compared to the control group

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3
Q

Relative risk RR definition and equation

A

Ratio of the probability of an event occurring in the Tx group compared to control group

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4
Q

Number needed to treat or NNT definition and equation

A

NNT is number of individuals that need to be tx to prevent a negative outcome in 1 patient
NNT = 1/ARR

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5
Q

A confidence interval that crosses ____ or a P-value > erro cuttoff value _____ denotes a result is NOT statistically signification

A

crosses the null value (often solid line)

P value >0.05

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6
Q

Study that is RETROspective; looks for odds of a previous exposure on the development of a rare dx manifestation.
Person has rare disease…lock backward at other groups that are otherwise matched, assess risk of exposure
What is a bias of this group?

A

Case Control Study

Recall bias

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7
Q

Odds ratio are used for Case Control
What is equation?
How is it used?

A

Start with those that have a disease; then look for chance of having an exposure
Odds ratio = Cases exposed/Cases not exposed
Controls expose/ controls not exposed

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8
Q

Study that is a ‘snapshot’ in time to determine whether or not they have a certain risk factor and PREVELANCE of certain disease of interest.

A

Cross sectional study

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9
Q

Categorizes patients with and w/o specific disease and compares the risk factor frequency between the two gruops

A

Case Control Study

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10
Q

Group of case reports regarding individual patients with similiar clinical manifestations or received similar tx; each case described in detail and may be used in rare disease or novel tx

A

Case Series

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11
Q

Study that follows individuals who do NOT have the dx/outcome of interests and who may or may not have a certain risk factor OVER TIME… study to assess disease development

A

Prospective cohort study

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12
Q

Occurs when an extraneous variable CHANGES THE DIRECTION OR STRENGTH of the effect the independent variable (exposure or treatment) has on the dependent variable(outcome)

A

Effect modification

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13
Q

An extraneous variable associated with BOTH the exposure and outcome obscures the association btwn exposure and outcome

A

Confounding bias

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14
Q

How can you tell the difference btwn effect modification and confounding bias?

A

Confounding bias has NO change in the strength or direction of the effect is seen with stratification; with randomization you mix up confounding variable

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15
Q

occurs when 2 disease interventions are compared and on intervention diagnoses the disease earlier than the other leading to erroneous presumption that there is an effect on the outcome

A

Lead time bias

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16
Q

Occurs when trials w/ significant positive results are published but trials with negative/null results are not

A

Publication bias

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17
Q

What does it mean when the standard error of measurement bars overlap btwn two samples?

A

Means there is a non-statistically significant difference

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18
Q

The applicability of a study’s results beyond the group that was initially assessed; ‘How generalizable are the results of the study to other populations?”

A

External Validity

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19
Q

Relates to conclusions regarding cause and effect in a study; answers question ‘are we observing/measuring what we think we are measuring/observing?”; threat to this is counfounding

A

Internal validity

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20
Q

The ability to detect an effect if that effect exsists. Depends on sample size; bigger is better

A

Power

the Effect Size = standard deviation

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21
Q

Non overlapping confidence intervals always imply statistically significant DIFFEReNCE BUT; the ones that do overlap:

  • 0.39 % (95% -0.58, -0.07)
  • 0.51% (95% -0.71, -0.14)
A

may or may not have statistically significant difference.

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22
Q

Increase for ___when multiple simultaneous hypotheses are tested at set p values
Ie testing multiple secondary endpoints increases probability of erroneously finding a statistically sig result

A

Type I errors (false positives) or alpha; probability of rejecting a null hypothesis when it is in fact true

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23
Q

Measurement of inter-rater RELIABILITY or extent to which inter-rater agreement is an improvement on change agreement alone

A

Kappa stastic

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24
Q

Intention to treat analysis is that participants in trials should be analyzed in the groups they were randomized, regardless of whether they received or adhered to allocated intervention and regardless if they withdrew, this helps prevnt..

A

Crossover and dropout and overall preserves randomization

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25
Q

Represents failure to reject a null hypothesis when it is false. dependent on the power of a study which depends on sample size

A

Type II error

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26
Q

Phenomenon when pts symptoms are alleviated by otherwise ineffective tx likely due to individual expecting the tx to work

A

placebo affect

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27
Q

Correlation coefficient (r) ranges from values -1 to +1 which indicates a positive or negative direction of association between 2 variables
0 is _____
____ is a strong association

A

0 is null value

-1 to +1 is stronger association; -1 is negative correlation while +1 is positive correlation

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28
Q

What does SnNout stand for

A

Test with high Sensitivity, a Negative results will help rule OUT a diagnosis

29
Q

What does SpPin stand for

A

Given a test with high Specificty a Positive result would help to rule IN a dx

30
Q

An epidemiological parameter that doesn’t vary with disease prevalence, provides clinically useful information for individual patients.
= a probability of a given test result occurring in a pt with a disorder compared to the probability of the same result occurring in a patient without the disorder

A

Likelihood Ratio

31
Q

How to calculate likelihood ratio from sensitivity and specificity

A

Postive test result = Positive LR = sensitivity / (1-specificity)
Neg Test result: Negative LR = (1-sensitivity)/ specificity

32
Q

when a study uses gold standard testing selectively in order to confirm a positive (or negative) result of preliminary testing. This can overestimate or underestimates sensitivity or specificity

A

Verification bias

33
Q

when control group unintentionally receives the tx or intervention, thus reducing the difference in outcomes btwn control and tx group.

A

Contamination bias

34
Q

What method of analysis is good in clinical trials with high drop out or non-compliance?

A

Intention to treat; you include all subjects as initially allocated after randomization, regardless of what happens during study period.

35
Q

The goal of this trial is to prove that a new drug or intervention is not unacceptably worse than an alternate drug or intervention.

A

Noniferiority trials

36
Q

On data from subjects who completed the intervention originally allocated at randomization are analyzed

A

Per protocol analysis; you end up losing benefit of randomization and will overestimate the real effect of the intervention

37
Q

The likelihood of an event occuring in a treatment group relative to the control group

A

Hazard ratio

38
Q

The null value for hazard ratio (HR) =

A HR that is _____ indicates event is less likely to occur in tx group than control group

A

The null value for hazard ratio (HR) = 1.0

A HR that is < 1.0 indicates event is less likely to occur in tx group than control group

39
Q

In order for confidence intervals to be statistically significant…

A

They need to NOT include the null value (1.0)
Significant ~ CI 0.32-0.69
NOT sigfniciant~ CI 0.72- 1.2

40
Q

Proportion of people with a particular condition who end up dying from that condition

A

Case fatality ratio

41
Q

Proportion of people in whom an illness develops out of the total population at risk for the disease

A

Attack rate

42
Q

burden of disease measure that evaluates the impact of specific diagnoses/treatment son indivdual or economic impact on health intervention on population.
Years of life lost and lived with diability used for..

A

Quality adjusted life years or QALY

Use ‘Time Trade Off’ of TTO; so 5 years in disable condition = 1 year of normal health

43
Q

burden of disease measure that evaluates the impact of specific diagnoses/treatment son individual or economic impact on health intervention on population.
These reflect the difference between the current situation and the ideal situation; ie living in perfect health up to standard of life expectancy; commonly used in global disease burdens

A

Disability adjusted life years (DALY)

Use years of life lost and years lived with disability used for this calculation

44
Q

In a case control study, we commonly use ____ as a measure of association

A

Odds ratio

45
Q

Type of study design that is experimental and utilizes >2 interventions and all combinations of these interventions

A

Factorial

46
Q

type of study that generally is observational in which a specific population or group is studied at one specific point in time, thus gives a picture of the whole group at that particular point in time

A

Cross sectional

47
Q

Form of retrospective observational study in which subsets of controls are matched to cases and analyzed for variables of interests

A

Nested study

48
Q

Seeks to determine whether an intervention works in real life conditions

A

Pragmatic study

49
Q

evaluates the association between a quantitative dependent variable and independent variables of interest while controlling for the effects of the other factors

A

Multiple linear regression

50
Q

results when an external variable has a positive or negative impact on the observed effect of a risk factor on disease status

A

Effect modification
Stratification can help detect effect modification
you should report separate measures of outcome

51
Q

A univariate analysis does not adjust for ____ while a multiple regression analysis does

A

confounding factors

52
Q

In a patient population with low disease prevelance the positive predictive value is likely to be low due to …

A

higher number of false positives relative to true positives

53
Q

Inciting pathologic events or exposures to risk sometimes occurs years before clinical manifestations become apparent… thus we monitor over time. Phenomonon…

A

concept of latent period

54
Q

In highly skewed distribution, the best measure of central tendancy is..

A

mean

55
Q

In highly skewed distribution the best measure of Central Location is

A

median

56
Q

refers to repeating primary analysis calculations after modifying criteria or variable ranges; goal is determine whether modifications significantly affect intial results

A

Sensitivity analysis

57
Q

Occurs when a test diagnoses a disease earlier than another does resulting in time from diagnosis until death appears to be prolongued but its not

A

lead time bias

58
Q

systemic differences btwn groups in term of treatment response or prognosis

A

selection bias

59
Q

Test to study difference in mean values among several different groups

A

Analysis of Variance or ANOVA

*must have homoscedasticty or homogeniety of variance for the test to be valid

60
Q

What does teh F statistic mean in ANOVA test

A

based on variation w/in and btwn different groups; used to obtain p value

61
Q

Can test difference between two paired means; patietns serve as their own control; ie mean BP before and after tx in same subject

A

Paired T-test

62
Q

___% patients lie w/in 1 STD of mean
___% patients lie w/in 2 STD of mean
___% patients lie w/in 3 STD of mean

A

68%
95%
99.7%

63
Q

A cross sectional study will look at + vs negative risk factors and compare…

A

disease PREVALANCE

64
Q

A Prospective cohort study will look at + vs - risk factors and compare…

A

Disease INCIDENCE

65
Q

A ____ will select patient with a particular disease and patietnts without disease and then retrospectively determine exposure status

A

Case (disease) Control (not diseased)

66
Q

Action taken before a patient develops a disease and targeted at preventing outcomes of the disease itself at initial stage

A

Primary prevention

67
Q

Action that attempts to halt progression of disease at it’s initial stage before irreversible changes take place to prevent complications

A

Secondary prevention

68
Q

____ in funnel plots suggest publication bias

A

Asymmetry

69
Q

Repeating primary analysis calculations by modifying certain criteria or variable ranges to determine if modifications significantly initial results

A

Sensitivity analysis

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