44 Statistics and Patient Safety Flashcards
type 1 error
rejects the null hypothesis incorrently, falsely assumed there was a difference when no difference actually exists
type 2 error
accets null hypothesis incorrectly, 2/2 small sample size, tx are interpreted as equal when there is actually a difference
null hypothesis
hypothesis that no difference exists between groups
p value
convention is <0.05 rejects the null hypothesis … mean 95% likelihood that the difference between the populations is true … <5% likelihood that the difference is not true and occurred by chance alone
variance
spread of data around a mean
parameter
population
mode
most common value
mean
average
meadian
middle value, 50th percentile
trials and studies: list types
RCT, double-blind controlled trial, cohort study, case-control study (retro), meta-analysis
randomized controlled trial
prospective study with random assignment to treatment and non-tx groups, avoid treatment biases
double-blind controlled trial
prospective study in which patient and doctor are blind to treatment, avoids observational biases
cohort study
prospective study - compares disease rate between exposued and unexposed groups (random assignment)
case-control study
retrospective study in which those who have the disease are compared with a similar population who do not have the disease, the frequency of the suspected risk factor is then compared between the 2 groups
meta-analysis
combines data from different studies
list quantitative vs qualitative variables
quant = student’s t test, paired t test, ANOVA … qual = nonparametric statistics, chi-squared, kaplan-meyer
student’s t test
2 independent groups, variable is quantitative - compares means
paired t test
variable is quantitative, beore and after studies (i.e. weight before and after drug vs placebo)
ANOVA
compares quant variables (means) for more than 2 groups
non-parametric stats
compare categorical (qualitative) variable (i.e. race, sex, medical problems and diseases, meds)
chi-squared test
compares 2 groups with categorical (qualitative) variables - i.e. number of obese patients with and without DM versus nonobese pts with and without DM
Kaplan-Meyer test
small groups, estimates survival
relative risk
incidence in exposed / incidence in unexposed
power of test
probability of making the correct conclusion = 1 - prob of type 2 error (accepts null incorrectly) … likelihood that the conclusion of the test is true … larger sample size increases power of test
prevalence
number of people with disease in a population (i.e. number of pts in US with colon CA), long-standing disease increases prevalence
incidence
number of new cases diagnosed over a certain time frame in a population (i.e. number of pts in US newly diagnosed with colon CA in 2003)
TP, TN, FP, FN 2x2 table
L: disease present and absent …. top: test positive and negative
sensitivity
ability to detect disease = TP / (TP + FN) … note denominator is the actual number of pts in the population with the disease … indicates the number of people who have the disease who test positive …. with high sens, a negative test results mean pt is very unlikely to have the disease
specificity
ability to state no disease is present = TN / (TN + FP) … note denominator is true number of pts in population without disease … indicates the number of ppl who do not have the disease who test negative … which high spec, a +test result means pt is very likely to have the disease
PPV
TP / (TP + FP) … denom is all + tests … likelihood that with a positive test, the patient actually has the disease
NPV
TN / (TN + FN) … denom is all neg tests … likelihood that with a negative test result, the pt does not have the disease
accuracy
(TP + TN) / (TP + TN + FP + FN) … denom is whole population … note denominator
predictive value
depends on disease prevalnce
sensitivity and specificity - relation to prevalnce
independent
goal of NSQIP
NSQIP = national surgical quality improvement program … seeks to collect outcome data to measure and improve surgical quality in the US … outcomes are reported as observed vs expected ratios
JCAHO prevention - use, protocol
aim to prevent wrong site, procedure, patient … protocol = preop verification of patient and procedure, operative site and side (marking if L or R or multiple levels, must be visible after the pt is prepped) … time out before incision is made (verify pt, procedure, position site and side, availability of implants or special requirements)
what promotes a culture of safey
confidential system of reporting errors, emphasis on learning over accountability, flexibility in adapting to new situations or problems
risk factors for retained object after surgery, MC object
MC retained sponge … emergency surgery, unplanned change in procedure, obesity, towel used for closure
define sentinel event
defined by JCAHO - unexpected occurrence involving death or serious injury or the risk thereof –> hospital undergoes RCA to prevent and minimize future occurences (i.e. wrong site surgery)
GAP protection technique
gaps in care (i.e. change in caregiver, divisions of labor, shift changes, transfers) can lead to loss of information and error … prevention = structured handoffs and checklists (face to face if possible), standardizing orders, reading back orders if verbal
