Biostats

Question 1

What is a case control study?

Answer 1

Select pts with dz (cases) and those wo dz (control) and RETROSPECTIVELY determine exposure

Question 2

What is a cross sectional study?

Answer 2

Prevalence study. Ie a survey.

Of looking at ppl w heart disease and then making them go thru img test to calculate their calcification score

Question 3

What types of prevention are there? Primary, secondary, tertiary? Primordial?

Answer 3

Primordial- before risk factor develops
Primary - for those at risk, before disease develops
Secondary halt disease process
Tertiary when disease has become advanced and now try to limit disability- ie cabg or pulm rehab
Quarternary preventions - HEALTH SYSTEM- using EMR to prevent extra catheterization

Question 4

95% of pts lie within how many standard deviations?
99.7%?
68%?

Answer 4

2 standard deviations from the mean
3 SD
1 SD

Question 5

Funnel plot is used to asses what type of bias?

Answer 5

Publication bias
X axis has treatment effect, y axis is standard error
No bias means 95% of the studies lie in triangle
Larger studies are at top and narrow spread bc more powerful. Smaller studies wide and on the base of triangle

Question 6

Funnel plot is used to asses what type of bias?

Answer 6

Publication bias
X axis has treatment effect, y axis is standard error
No bias means 95% of the studies lie in triangle
Larger studies are at top and narrow spread bc more powerful. Smaller studies wide and on the base of triangle

Question 7

What is best answer for the NET CLINICAL BENEFIT of a drug??

Answer 7

Answer should include the beneft and harm (ie intracranial bleed). Not just the benefit.

Question 8

Important features of randomized controlled trials include randomization, blinding, and intention to treat analysis. ITT is to preserve what

Answer 8

Randomization. Regardless of if they drop out or die or didnt finish tx

Question 9

What is external validity?

Answer 9

How applicable the results are or how representative they are to the desired population

Question 10

What is type II error?

Answer 10

When a study FAILs to reject null hypothesis that is false. Depend on power of the study to detect a difference when a difference exists.

Question 11

Which is better measure of central tendency in a strongly skewed distribution? Mean or median?

Answer 11

Median

If normally distributed then mean is best.

Question 12

What is type I error?

Answer 12

False positive

Study incorrectly rejects null hypothesis that is true

Reflects the significance

Question 13

Define: Case fatality

Mortality

Answer 13

Case fatality is porportion of ppl on specific gp who die

Mortality is prob dying from condition in general population

Question 14

What would using one tailed test do to the power?

Answer 14

Incr power bc only look at effect in one direction

When you see alpha, that is the p value or statistical significance

Question 15

How to calculate incidence ratio?

Answer 15

Number of observed cases/expected cases

Question 16

What test uses p value and F to study mean values between groups?

Answer 16

Anova - analysis of variable

Fischers test only when small sample

Mcnemar test comparing two proportions where pts serve as own control

Question 17

Case control studies measure what?

Answer 17

Association

Question 18

How to calculate relative risk?

Answer 18

Risk in exposed/risk in unexposed

Question 19

What is attributable risk? Ie what percent of ischemic strokes observed in SMOKER is attributed to smoking status?

Answer 19

Risk in exposed - risk in unexposed / risk in exposed

Question 20

What is population attributable risk percent ? Ie what percent of ischemic stroke observed in the POPULATIon is attributed to smoking?

Answer 20

Risk in total population - risk in unexposed / risk in total population

Question 21

When does a result become NOT statistically significant if there is CI?

Answer 21

If included null value of 1

Question 22

In order to calculate Ntt, how to calculate arr?

Answer 22

Risk in group-risk jn placebo. Then ntt is 1/arr

Question 23

When asked to find group with selection bias, what do you look at?

Answer 23

The N in both the observed group and treatment group should all be accounted for. If only 33% of the ppl had their ferritin levels measured then that is not representative of the target population

Question 24

A study shows significance in use of new inhaled agent with mean number of rescue uses 22.6 vs 24.1 withh p value 0.04. What does this study lack?

Answer 24

Clinical significance!!

Just like how a new antihtn which lowers significantly by 0.5 mmhg doenst matter

Question 25

How to calculate
Positive likelihood ratio
Neg likelihood ratio

Answer 25

Positive likelihood = sensitivity/(1-spec)

Neg likelihood= 1-sense/spec

These do not depend on prevalence

Question 26

When a study uses a test ie colposcopy on pap abn women and also performs pap on women w normal pap what is this trying to reduce

Answer 26

Verification bias

Question 27

What is smr the standardized mortality ratio?

Answer 27

Number observed deaths/expected number deaths

Question 28

What is this kind of study
Crossover study
Cross sectional
Factorial study

Answer 28

Crossover is experimental where expose to diff tx sequentially

Cross sectional is observational

Factorial study is experiment where use more than 2 interventions in all combinations. Je randomize pts to glutamine, antioxidants, both or nothing

Question 29

sensitivity vs ppv

Answer 29

Sensitivity is percent of predicting dz if it is present

Vs ppv is ratio of having the disease given positive result

Question 30

Rr of 0.4 can be thought of as what percent

Answer 30

40%

Question 31

Odds ratio

Answer 31

Odds are lower!!

Ie 0.25

Question 32

How to calculate NNH

How to calc attributable risk

Answer 32

Need artributable risk incidence of dm in exposed minus incidence in nonexposed

18.9/1000-16.9/1000=0.002
NNH = 1/Atrributable risk=500

Question 33

Screening test should have high

Answer 33

SeNsitivity!!!! To rule out

Question 34

If the tail (less side) is to the right then the orders of mean median node are from left to right

Answer 34

Median mode mean