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USLME Kiss my ass and pray > Biostats > Flashcards

Biostats Flashcards

1
Q

APGAR

A 
Appearance
Pulse
Grimace
Activity
Respiration

1 and 5 min
>7 good, 4-6 assist, < 4 resuscitate

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2
Q

Sensitivity

A

TP/(TP +FN)

-set up a 2x2
Sensitivity rules out - If negative, very likely not going have. Too sensitive of a test you are going to have many false positives.

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3
Q

Specificity

A

TN/(TN+FP)

Sp -in rules in. If positive likely positive test

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4
Q

1-statisitcal power =

A

Type II error

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5
Q

Odds ratios are calculated in what type of study

A

Case control

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6
Q

Relative risks are calculated in what type of study

A

Cohort studies

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7
Q

How does odds ratio relate to Relative risk?

A

Odds ratio is an approximation of relative risk because you cannot know the entire population in a case control. In a cohort the population is defined and risks can be calculated

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8
Q

Case control study is looking for what?

A

looking for risk factors and exposures that are in common in a group of people with a disease in comparison to those without the disease

it is retrospective and observational

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9
Q

Cohort study is looking for what

A

it is comparing those that have an exposure or risk to those without and seeing what becomes of it

It is observational and can be prospective or retrospective (form a cohort after an exposure and follow then)

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10
Q

Cross sectional study gives what about a disease

A

the prevalence

a snapshot in time of those that have the disease, can start looking at associations w/ risks to determine correlations

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11
Q

Twin concordance studies measures what?

A

heritability

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12
Q

Clinical trials can be improved w/ what 3 design strengtheners

A

Control group
Randomization
Double blind

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13
Q

Phase I of a drug trial asks

A

Is it safe

Tests on healthy people for toxicity and pharmacodinamics

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14
Q

Phase II of a drug trial asks

A

Does it work

Test on sick people for efficacy, dosing and adverse effects

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15
Q

Phase III of a drug trial asks

A

Does it work better

Large #s of people and clinical trials

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16
Q

Phase IV of a drug trial asks

A

What else can go wrong?

Post market surveillance

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17
Q

Meta analalysis

A

Pooling together of different studies based in inclusion criteria to gain statistical power

-some selection bias and concern for individual merits of the studies

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18
Q

Sensitivity tests what?

Formula

A

Sensitivity tests proportion of those that test positive to the disease and compares to ALL that have the disease

TP/(TP + FN)

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19
Q

Specificity Tests what?

Formula

A

Specificity tests the proportion those that test negative to the disease compared to ALL those that do not have the disease

TN/(TN+FP)

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20
Q

Positive predictive value tests what?

Formula

A

PPV compares those that test positive and actually have the disease to the the proportion of ALL those that test positive to the disease

TP/(TP and FP)

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21
Q

negative predictive value tests what?

Formula

A

NPV compares those that are actually disease free to the proportion of ALL those that test negative to the disease

TN/(TN + FP)

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22
Q

How does Specificity and sensitivity change with prevalence?

A

They don’t. Specificity and specificity are limited to the categories of those that either have the disease or don’t.

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23
Q

How does PPV and NPV change with prevalence?

A

With increased prevalence the PPV increases and NPV decreases.
-testing in an area where there is a lot of disease you are more likely to believe a positive test over a negative test

With a decrease in prevalence, the PPV decreases and NPV increases.
-Testing in an area where there is not a lot of disease. more likely to believe the negative test than the positive test

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24
Q

Given only the false negative %, what is the sensitivity?

A

1 - FN

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25
1 - False Positive% =
Specificity
26
Which test do you use to screen for and which do you use to confirm?
you screen with a highly sensitive test because you want to catch all the positives. May have some FP. You you then run a high specific test which is looking for those that are negative(Specific tests are those comparing those that are truly neg compared to all those that test negative); if you test negative you are negative in the disease and eliminates FP from the sensitive screen
27
what is incidence? Formula
Incidence is the amount of new cases found in a population at risk of cases/those at risk (minus those w/ disease)
28
what is prevalence? Formula
prevalence is the amount of people with a disease (all cases) in a population at risk of existing cases /population at risk
29
How does time course of an illness affect prevalence and incidnce
incidence = prevelence x time course The shorter the disease duration the smaller the prevalence. Ex: the flu Chronic disease may have a low incidence but a high prevalence (COPD, DM)
30
ODDs ratio formula?
odds ratio is the odds that a group exposed to a risk will develop the disease compared to those that are not exposes - case studies (a/b)/(c/d)
31
Relative risk formula
RR is the incidence of a disease in a population exposed to a risk divided by the incidence of a disease in those not exposed - Cohort [a/(a+b)] / [c/(c+d)] RR -> OR when the prevalence of the disease is really small ( a and c are minuscule)
32
Attributable Risk is ? Formula Associated w?
the difference between incidence of those that are exposed to a risk with a disease compared to those that are not exposed a/(a+b) - c/(c+d) Associated w/ Number needed to harm which is 1/AR
33
Absolute risk reduction is? Formula? Associated w?
the difference between the incidence of the disease in those NOT exposed to a Rx to compared to those that are c/(c+d) - a/(a+b) Associated with number needed to treat 1/ARR
34
Number needed to treat
Determines the cost effectiveness of a treatment. Number of people that get treatment before having one positive effect 1/Absolute risk reduction 1 / [c/(c+d) - a/(a+b)]
35
Number needed to harm
determines the number of people needed to be exposed to a risk before before disease 1/ Attributable Risk 1 / [a/(a+b) - c/(c+d)]
36
precision is
the reproducibility/repeatability of a test May not be accurate
37
Accuracy is?
the truthfulness of a test may not be precise/reproducible
38
Selection bias
nonrandom assignment to participation in study | -ex may be those reffered to a study are closer to end stage disease
39
Berkons bias
subtype of selection bias where selection of patents are more likely to be hospitalized - selection skewed since those selected were more likely to be hospitalized anyways
40
Recall bias
knowledge of a disorder impacts the ability to recall detail for a study Ex parents of autistic kids remember more than parents of kids w/o autism
41
sampling bias
subjects are not representative of the target population ex - avg age of participants is less than avg age of target group
42
Late look bias
information gathered in a timeframe that preferentially selects for this w/ more indolent course of disease; severe cases dead and limits generizability
43
Procedure bias
Subjects are not treated the same in a clinical trial ex: experimental drug rx may receive extra couching and disease education compared to controls
44
Lead time bias
esp pertinent to screening studies - falsely attributing increased survivability when in fact early screening only found the disease sooner natural course of the disease has not changes
45
observer expectancy effect/pygmalian effect
the confidence of the researchers assumption of the results of a study influences the study to match expectations. Not malignant in change, maybe participants conform to thought
46
Hawthorne effect
disruption of truthfulness of the study due participants knowledge of being observed ex: hand washing frequency
47
confounding error
when there is a 3rd variable related to the variable tested and the measure result that either modifies or magnifies the result Something else may be going on
48
Cross over study
patient serves as their own control. Take both the experimental and control substance unknowingly to determine effect
49
positive skew in a distribution
tail to the right meaning the mean>median>mode
50
negative skew in a distribution
tail is to the left meaning the Mean< mode
51
maintain Ho when H1 is true
False negative or type II error (beta) falsely saying nothing is going on with 2 variables when in fact there is a relationship
52
alpha in biostatistics
is type I error - making a statement that there is an association when in fact there isn't; rejecting Ho for H1 when Ho is true alpha is a usually selected at 0.05 for the cut off of risk of making a type 1 error- 5 % chance of saying there is something going on when there is not. p needs to be less than 0.05
53
beta in biostatistics
type II error - making a statement that there is nothing connecting 2 variables when there is something a false negative
54
p value
is probability calculated from the data the the results are due to chance alone. Compared to alpha value and usually needs to be less than 0.05 If so then, you are safe to reject the null hypothesis, for there it is unlikely that there is nothing going on and an alternative hypothesis must be accepted
55
Power in biostats
1- beta(or type II error) the probability of falsely rejecting a null hypothesis when it is in fact false. -or the likelihood of finding a difference if one in fact exists. empowering your decision to reject null, increase power, increase rationality that it is ok to reject null
56
Increase power how?(3)
increase sample size increase expected effect size increase precision of measurement
57
% of population w/in? 1 SD 2SD 3SD
1SD- 68% 2SD -95% 3SD - 99.7%
58
SEM =?
SD/ square root (n) n = population - as n increases SEM decreases (less error) used in calculating Confidence intervals
59
Confidence interval -
Mean +/- Z x (SEM) ``` Z= 1.64 w/90% Z= 1.96 w/95% Z= 2.5 w/ 99% ```
60
When to not reject Ho with a confidence interval
When confidence interval includes 0 When CI for an OR or RR includes 1
61
t test?
checks difference between the means of 2 groups of continuous variables (i.e weight)
62
ANOVA
checks the difference between the means of 3+ groups of continuous variables (i.e. weight)
63
Chi Square
tests the difference between 2 or more percents or proportions of categorical incomes ex: yes/no; age 50-59 vs 60-69; men vs females
64
r
is pearsons correlation which can range from -1 to 1 the closer the value is to the 1 the stronger the positive correlation that exists between 2 variables 0 = no correlation
65
Coefficient of the determinent
=r squared the goodness of bit and variance within the data pts. reflects the proportion of variance in y that is due to variance in x
66
Car seat recommendations
) booster
67
Vaccines in kids 0-6(10)
``` Hep A Hep B Rota DTP HiB Varicella Pneumococi IPV influenza MMR ```
68
Vaccines in kids 7-18 (4)
TDaP -> Td q 10yrs meningococcus HPV Influenza
69
Vaccines in adults
``` influenza Herpes zoster > 50 pnumococci >65 Meningococci Hep A and B if liver damage ```
70
Screening recommendations in adults age 50
``` Colon q 10 yrs Depression BP dyslipidemia DM Obesity Tobacco and alcohol ```
71
ASA use for preventative measures?(2)
45-79 - daily in Men for MI 55-79 daily in women for Stroke
72
Kubler Ross grief stages (5)
DABDA ``` Denial Anger Breievment Depression Acceptance ```
73
When does grief become pathological
depression criteria med at least 2 weeks after the 1st 2 months generalized feelings of hopelessness, helplessness, worthlessness, and guile Suicidal Distreessed feeling > 6 months inability to move on > 6 months
74
3 leading causes of death in adults > 65
CA Stroke Heart disease
75
Odd recommendation for AAA screening
1 US for men 65-75 who have ever smoked
76
OSteoperosisis screening
DEXA scan q 2 yrs older than 65
77
PAP smears age
start age 21 end age 65
78
Mammogram screening age
~50-75
79
Reportable diseases (5)
``` STDs - Chlamydia, gonorrhea, Shyphilis HIV Hep A, B and C Diarrheal - salmonella and shigella vaccine preventable diseases like mumps TB ```
80
What does not change in the elderly (2)
``` Sexual interest (may have mech issues though) intelligence ```
81
Changes in sleep with elderly(3)
increased latency and awakenings Less REM and N3 (deep sleep) total sleep time declines

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