CHAPTER: Stats//Behavioral Flashcards
Type of study that measures odds ratio - whats the equation
Case control Retrospective (why can't calc RR) Exp grp = cases = diseased Control = disease FREE OR = ad / cb
Type of study that measures relative risk - equation
Cohort study
Prospective or historical
RR = (a/a+b) / (c/c+d)
Evaluation of the people who got the disease in some way (what put these people at higher risk?!)
Name phase 1-4 of a clinical trial
1 = is it safe = healthy vol 2 = does it work = small grp pts w/ disease 3 = is it as good or better = randomly assigned to treatment v placebo 4 = cant it stay = post-marketing surveillance for long term adverse SE
What is an ecological survey?
Study of POPULATIONS
How frequently does x pair with y outcome in pop data
What is a cross over study
Rd 1 = a placebo and trt grp
Washout
Rd 2 = grps get the other treatment
Pro = pts serve as own controls
In a 2x2 table, what is the x vs y axis
X = disease +/- Y = test, RF or intervention +/-
Equation for incidence + prevalence - which value is affected by disease recurrance
Incidence = # new cases/#people @ risk
Prev = #existing cases / total # ppl
Only prevalence is affected by recurrence (add some back into existing case pool)
Similarly, cures + death only remove from existing cases
If a drug ↑survival but does not cure: ↑prev, no change incidence
What is AR + equation
Proportion of disease occurrences attributable to the exposure
AR = (a/a+b) - (c/c+d)
AR is subtraction, RR is division
Equation relative risk reduction
Proportion of risk reduction due to intervention
RRR = 1-RR
Absolute risk reduction equation
Difference in risk due to intervention
ARR = event rate (control) - ER (trt)
ARR = (c/c+d) - (a/a+b)
ER is one of those two variables, don’t separate a+b values
Switch the AR equation
Define + equation NNT
NNT for 1 pt to BENEFIT
NNT = 1/ARR
Define + equation for NNH
# pts need to be exposed to a RF for 1 pt to be harmed NNH = 1/AR
Another word for precision is…
How does precision change with random error, SD
Precision = reliability (how close 3 hits are)
↑Random error ↓precision
↑precision - ↓SD (duh)
Another word for accuracy is… what type or error changes accuracy?
Accuracy = validity (are you on the target)
Does this test measure what it should
Systemic error ↓accuracy
What is procedure bias? How reduce it
Different grps not treated the same
Ex: trt grp spent more time in a specialized hospital
BLIND + PLACEBO
What is the Pygmalion and Hawthorne effects? How reduce
Pygmalion = researcher’s belief changes outcome (self fulfilling prophecy)
Hawthorne = subject behavior changes as they know they are being studied (ex: doctors in a quality control study)
Blinding + placebo
Best way to control confounding
Matching
What type of bias should you keep in mind for screening tests
Lead time bias - did this screening test actually extend someone’s life or just detect the disease earlier
What is the mean, med, mode in normal dist vs positive skew vs negative skew
Normal dist: mean = med = mode
+ skew = hump to L, long tail to the R
mOde E > O
What is a type 1 error? Alpha?
T1 error = false positive
You said there was an effect but none exists
Alpha = probability making T1 error
Why do you compare alpha to the p value?
If p
What is a type 2 error? Beta?
False neg
You said my data is cramp, but it really isn’t! There is an effect
B = probability making T2 error
What is power? 3 ways to ↑power?
Power = 1-B Ability to detect a difference when one really exists (you're subtracting the likelihood that you don't ID a relationship) ↑power if you ↓B 1. ↑SS (pwoer in #s) 2. ↑expected effect size 3. ↑precision of your tests
If CI = mean +/- Z(stand error of mean), what is Z for a 95 vs 99% CI?
95% CI, Z = 1.96
99% CI, Z = 2.58
