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Statistics 1

UWORLD + FA Statistics Review

QuestionAnswer
Correlation coefficients range from ____ to ____, and are used to describe ________________ and ________________ of a linear association. The ________________ to ___ or ____, the ______________ the association. -1 to +1; strength and polarity; Closer to -1 or +1; STRONGER
What kind of cancer is the most common in men and women? Lung cancer
What is the most important factor for lung cancer development? Tobacco use
Order of female cancer mortality Lung> Breast> colon> Pancreas> stomach
Sensitivity is? Refers to the ability of the test to identify those with the disease.
Screening for a life-threatening diseases, prefer a __________ ________________ test. High sensitive
A sensitive test yields a ________ number of _______________ which helps to __________________. High number of False positives; Rule OUT
What is the reason of an SPECIFIC test? It is the ability to identify those without the disease
Specific test yield a ________ number of __________________, which helps to ____________________. Low number of False positives; Rule IN
Low false-negative is related to Sensitivity
A person who has a disease or might have it test positive Sensitivity
Sensitivity Rule out
Specificity Rule in
Sensitivity equation = TP /(TP + FN)
Proportion of all people without the disease who test negative, or the probability when the disease is absent, the test is negative. Specificity
Low-false positive rate Specificity
______ ____________ test is used after a positive screening test High Speficific
Specificity equation: = TN/(TN + FP)
PPV Positive Predictive value
Probability of a person that test positive actually has the disease PPV
PPV varies directly with: Pretest probability
High pretest probability = High PPV
NPV varies _________________ with ______________ and ____________. INVERSEBLY; pretest probability and Prevalence
Case-fatality rate is a measure of? Severity of a condition
Number of DEAD by condition divided by number of people alive with the condition. Case-fatality rate
Ignorance of the test accords Blinding technique
A blinding technique reduces the: Observer bias
What is recall bias? Study participants inaccurate recall of post exposure and happens in most POST-EXPOSURE studies such as case-control studies.
What kind of study is used in order to reduce recall bias? Prospective study
Study done in order to record the initial exposure status and have tight control Prospective study
____________________ bias is NOT representative of the general population. Selection bias
What are the Observational studies? Cohort (retrospective and prospective), case-control, cross-sectional, and ecological studies
Cohort studies are also referred as _________________ studies. Longitudinal
What are the subcategories of Cohort studies? Retrospective and Prospective studies
Retrospective studies are affected by: Recall bias
What value/unit answers the question, 'What is the probability that a patient has a disease?'? PPV
What is the main determination of the Cutoff value? Measure whether a result is interpreted as positive or negative
Lowering cut off value: - moves midline to the LEFT - Increase False Positives and Sensitivity - Decrease False Negatives and Specificity - Increase NPV and Decrease PPV
What happens with an increase in cutoff value? - moves midline to the RIGHT - Increases false negatives, Specificity, and PPV - Lowers false positives, Sensitivity, and NPV
What is the equation for Power? = 1-B
Power: Measures the probability of rejecting a null hypothesis when it is truly false
What are the 2 important factors that determine Power? 1. Sample size 2. Difference between outcomes
Power normal value is usually at 80%
B-error probability of making a type II error
Investigated to reject a null hypothesis, when it is really true Type I error
What kind of error is encountered in when investigator find a statistical difference where there is none? Type I error
What represents the maximum acceptable degree of type I error? a (alpha)
a(alpha) is usually compared to what other value? p-value
What is the usual value of "p-value"? 0.05 or 5%
Null hypothesis (H0); Hypothesis of no difference or relationship
Stating there is not a difference or relation where there really is one Type II error
B(beta): probability of making a type II error
B(beta) is related to ___________________________. Statistical power (1-B)
What is statistical power? The chance of rejecting a null hypothesis when it is false
What are the 3 factors that increase power and decrease B? 1. Increase sample size 2. Increase expected effect size 3. Increase precision of measurement
False-positive error is another way to refer to _______________. Type I error
Another way to refer to a Type II error? False- negative error
A 95% Confidence Interval (CI) corresponds to a _____________, which the most often used values. a(alpha) = 0.05
Range of values within the true mean of the population is expected to fall, with a specified probability? Confidence Interval (CI)
What is the most commonly used CI? 95%
What is the value of "Z" in a 95% CI? 1.96
What is the value of "Z" in a 99% CI? 2.58
If the 95% CI for 2 values includes 0: 1. There is NO significant difference 2. H0 (null hypothesis) is NOT rejected
If the CIs of 2 groups do not overlap, it means? There is a statistical difference
What is the meaning if the CIs of 2 groups overlaps? There is NO statistical difference
If the 95% CI of odds ratio and relative risk includes ______, then _____________________________. 1; H0(null hypothesis) is not rejected
What is the equation of chance is the probability is set at x and there is y number of samples? = x (to power of y); multiply x itself y number of times.
What is determined by a Case-control study? The EXPOSURE STATUS of people with disease (cases) to the exposure status of people without the disease (control).
What it is the main association of Case-control study? Odds ratio (OR)
What is the equation for odds ratio? = (odds of Exposure in cases)/ (odds of Exposure in control)
= ad/bc Odds ratio (OR)
Values (largest to smallest) in a NEGATIVELY skewed distribution . MEAN>>Median>> mode
Mean, median, and mode are arranged as __________________________________________ in a POSITIVELY skewed distrugion. mode> Median> MEAN
In a graphic depiction of a negatively skewed distribution, the graph "appears" to be ______________________ to the __________. PUSHED to the RIGHT
A positively skewed graph, appears to be ___________ to the ______. PULLED to the LEFT
In a normal (Gaussian) distribution, the normal SE account for the following percentages: 1 SE --> 68% 2 SEs ----> 95% 3 SEs --------> 99.7%
ANOVA: Analysis of variance
ANOVA is used to determine any significant differences between the _____________________ of ________________________. Means; 3 or more groups
A t-test is used in analysis of ______ groups. 2
What is the overall advantage of a Meta analysis? Gathers data of several studies, leading to greater statistical power.
What testo of analysis would be used to compare the blood pressure between men and women? t-test
Checks differences between 2 or more percentages or proportions of categorical outcomes Chi-square test
Chi-square does NOT measure the ________ values. Mean
In labeling a 2x2 square values for calculating ODDS RATIO, what are the description of the following: A+C --> total people with disease B+D --> total people without disease A+B --> total people with Exposure C+D --> toal people without Exposure
What is the attack rate: a ratio between people who contracted a disease divided by the people who is at risk of contracting the disease.
3 standard deviation account for ________% of the sample results. 99.7%
A result with 2 standard deviations is within what percentage of all the sample population? 95%
68% of all population in a result is withing how many standard deviation? 68%
What is risk? Probability of developing a disease over a certain period of time
How is risk calculated? = (number of affected subjects)/ (number of corresponding subjects in that group)
Relative Risk (RR) is usually a measure seen in ________________ studies. Cohort
Risk of developing disease in exposed group divided by risk of unexposed group Relative Risk (RR)
In what cases or situations OR approximates to RR? In rare diseases or those with low prevalence
What does an RR=1 means? No relation between the exposure and disease
RR < 1 means: Exposure associated with decreased disease occurence
RR of 1.5 would signify that: Exposures associated with INCREASED disease occurrence
RR is calculated by: = a/(a+b) / c/(c+d)
Difference in risk between the exposed and unexposed groups Attributable risk (AR)
= a/(a+b) - c/(c+d) Attributable risk (AR)
Risk of those in the exposed group is calculated by: = a / (a+b)
What would be the AR if lung cancer in smokers is 25% and lung cancer in nonsmokers is 10%? 15%
The proportion of risk reduction attributable to the intervention as compared to a control. Relative Risk Reduction (RRR)
If 3% of people who receive their annual flu vaccination developed the disease, and 12% of those who decided to remain unvaccinated developed the disease. What is the RR? and RRR? RR is 3/12 = .25 or 25%, and RRR is 1-RR, so, RRR=1-.25= 0.75
How is relative risk reduction (RRR) calculated: = 1 - RR
The difference in risk (not the proportion) attributable to the intervention as compared to a control Absolute risk reduction (ARR)
While AR is the difference (subtraction) of the risk of EXPOSED group minus the risk of those UNEXPOSED group, in ARR: The subtraction reverses the values of the subtraction, having the risk of UNEXPOSED - risk of EXPOSED
ARR is caluated: = C/(C+D) -- A(A+B)
NNT: Number of patients who need to be treated for 1 patient to benefit
What value is needed in order to calculate for NNT? ARR
What is the equation for NNT? = 1/(ARR)
One divided by the difference in risk (not proportion) attributable to the intervention as compared to a control. Number needed to treat (NNT)
What does it mean for the treatment quality, a low NNT? The lower the NNT, the better the treatment
Number of patients who need to be exposed to a risk factor for 1 patient to be harmed Number needed to Harm (NNH)
What value of risk is needed to calculate NNH? Attributable risk (AR)
What is the equation to calculate NNH? = 1/ (AR)
A high NNH number means: Safer exposure
The consistency and reproducibility of a test Precision
Another term used to refer to "PRECISION" Reliability
Trueness of test measurements accounts or describes _______________. Accuracy
Matching in a study is used for: Control confounding matching variables in a case-control study.
What are the potential (common) confounding factors associated with matching? Race, age, neighborhood, diet
Case control studies desire _____________________ variables, in order to approximate a similar distribution. Matching confounding
What is a "Prevalence" or a "Snapchat" study? Cross-sectional study
What is measured or researched in a Cross-Sectional Study? Exposure and outcome simultaneously of a particular POINT in TIME.
What kind of study is designed to answer the question, "What's happening?" Cross-sectional study
What is the MC measure appointed in a Cross-sectional study? Disease Prevalance
Frequency of disease and frequency of risk-related factors are assessed in the present Cross-sectional study
Cross-sectional study can show ______________________, but it does not establish _____________________. Risk factor association with disease; Casuality
A Case-control study is designed to answer what question? What happened?
Case-control study: Compares a group of people with disease to a group without disease
What is the value obtained in designing a Case-control study? Odds ratio
Odds ratio is often calculated in what kind of study? Case-control study
A cohort study answers the questions: 1. Who will develop disease? (Prospective) or, 2. Who developed the disease? (Retrospective)
What kind of study is designed to look to see if exposure or risk factor is associated with later development of disease. Cohort study
Compares a group with a given exposure or risk factor to a group without such exposure. Cohort study
Relative Risk (RR) is a measurement obtained in what kind of study? Cohort study
Study Design --------->Measurement: Cohort Study ------------------------------> Case-control study -----------------------> Cross - sectional study -------------------> Relative risk Odds Ratio Disease Prevalence
What bias is involved in recruiting of subjects? Selection bias
Methods used to reduce Selection bias? 1. Randomization 2. Ensure the choice of the right comparison/reference group
What is Berkson bias? A type of Selection bias, in which the selected population of a hospital is less healthy than the general population
What is the most common error leading to a Selection bias? Sampling bias
Nonrandom sampling or treatment allocation of subjects such that study population is not representative of target population Selection bias
What bias or errors are committed while performing the study? 1. Recall bias 2. Measurement bias 3. Procedure bias 4. Observer-expectancy bias
1. Confounding bias 2. Lead-time bias 3. Length-time bias Errors or bias that occur while interpreting the results
What is the most common bias seen in retrospective studies? Recall bias
Subject's awareness of disorder, is a predisposition to: Recall bias
A patient recently noticed a previous exposure to a specific risk factor after reading similar case in the newspaper. Recall bias
How is recall bias reduced? Decrease time from exposure to follow-up
What is the Hawthorne effect, and what does it lead up to? Participants behavior changes upon awareness of been observed, leading to Measurement bias
A faulty blood pressure cuff will lead to a ____________________. Measurement bias
A placebo group would reduce the ____________________ Measurement bias
Information is gathered in a distorted manner, either due to equipment malfunction or by odd or changing behavior of subject. Measurement bias
Pygmalion effect is: The belief of the researcher efficacy of the treatment, which results in changes in outcome of that treatment.
A physician with a daughter with terminal cancer, is in charge of research a new chemotherapeutic drug. This represents what kind of challenge to the study? Observer-expectancy bias may result due to strong need or desire of the physician.
An observer with strong desire of favorable outcomes is more likely to notice positive results. Observer-expectancy bias
Subjects in different groups are not treated the same Procedure bias
What are 3 methods or procedures used to reduce Confounding bias? 1. Multiple/Repeated studies 2. Crossover studies 3. Matching
Subject acts as their own controls Crossover study
Study in which participant is subjected to several sequence of treatments or exposures Crossover study
Patients with similar characteristics in both treatment and control group Matching
Confounding bias When a factor is related to both the exposure and outcome, but not on the causal pathway, it distorts or confuses effect of exposure on outcome
A wash-out period is seen in what kind of study design? Crossover study
If variable affects both, the exposure and outcome, is known as __________________ bias. Confounding bias
Confounding: A situation in which the effect or association between an exposure and outcome is distorted by the presence of another variable
When early detection is confused with increased survival Lead-time bias
Length-time bias: Overestimation of survival duration due to the relative excess of cases detected that are slowly progressing
Lead-time bias: Overestimation of survival duration due to earlier detection by screening than clinical presentation
In a slowly progressive cases of lung cancer, there is a chance of________________, due to ____________________________. Length-time bias; the slow progression of condition leads to a increased number of cases.
A quick and effective screening test for HIV infection, is a risk to the development of what kind of bias? Lead-time bias as it increases the "apparent " survival duration, but not the overall mortality rate.
Participants without the disease in a study. Control group
Previous exposures status is evaluated by _________ study. Case-control study
= Control rate - Case (treatment) rate ARR
= ARR/ (control rate) RRR
= (Treatment rate) / (control rate) RR
What is a case-series study? A descriptive study that tracts patients with a known condition to docucient the natural history or response to a treatment. It provides no statistical significance measurements
Most frequent value in a data set Mode
Value located in the precise center of an ordered data set Median
Average of all data set? Mean
In a positively skewed distribution, the greatest measurement of the data set is the _____________. Mode
What is meta analysis? The result of several trials to increase statistical power and provide overall pooled effect estimate
The null value is dependent on the _________. Confidence Interval (CI)
If the CI DOES NOT include the null value? Result is statistically significant
If the study or case is to reflect a DIFFERENCE in values, the null value is _____________. If the CI in this case does NOT include the _____, the results are __________________________. 0; 0; statistically significant
= (Absolute risk control) - (Absolute risk treatment) / (Absolute risk control) RRR
Created by: rakomi