BIOSTATISTICS ASSESSMENT EXAM QUESTIONS &
ANSWERS ALREADY GRADED A+ (BRAND NEW)
What is confounding? - CORRECT ANSWER >>>bias that can result when the exposuredisease
relationship is mixed with the effect of extraneous factors (i.e. confounders).
What is the NPV? - CORRECT ANSWER >>>probability of being free of a disease if the result is
negative
- varies wsith pretest probability
What is the purpose of randomization? - CORRECT ANSWER >>>method to control confounders
in the design stage of a study
- helps to control known risk factors as well as unknown and difficult-to-measure confounders
What is the Chi-square test? - CORRECT ANSWER >>>compares the proportions of a categorized
outcome
- ex) serum CRP level is either high or normal and is presented with the expsoure (HRT or no
HRT) in a 2x2 table.
- compared observed values with expected values
What is latent period? - CORRECT ANSWER >>>natural phenomenon (not a bias)
- infectious disease = short latency and chronic disease = long latency
- extended period of exposure may be necessary to affect outcome
- selection bias is a distortion in the estimation of exposure-disease relationship due to
inappropriate means of people selection for the study or due to selective losses from follow-
up what is susceptibility bias? - CORRECT ANSWER >>>type of selection bias where treatment
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, regiment is selected fore a patient based on the severity of their condition without taking into
account other possible confounding variables.
What is the purpose of matching cases with controls based on characteristics like age, race, etc?
- CORRECT ANSWER >>>reduce confounding variables
How is NNT calculated? - CORRECT ANSWER >>>NNT = 1/ARR
ARR = CER-EER
What is the affect of changing the cutoff value for a given condition? - CORRECT ANSWER
>>>alters the PPV, NPV, sensitivity, and specificity
- increased specificity correlates with increased PPV
- increased sensitivity corresponds to increased NPV
What is the affect of lowering the cut off point? - CORRECT ANSWER >>>increases teh
sensitivity of a test, but as a result, false positives will increase, so PPV will decrease and false
negatives will decrease
PPV= TP/TP+FP
Sensitivity = TP/TP+FN
Specificity = TN/TN+FP
How does prevalence affect PPV and NPV? - CORRECT ANSWER >>>PPV increases with an
increase in prevalence of disease in the study population
NPV decreases with increase in prevalence of disease in the study population
How is NPV calculated? - CORRECT ANSWER >>>TN/TN+FN
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, What is the two-sample t test? - CORRECT ANSWER >>>statistical method that is commonly
employed to compare the means of two groups of subjects
what is ANOVA? - CORRECT ANSWER >>>analysis of variance is used to compare three or more
means
What is the two-sample z test? - CORRECT ANSWER >>>used to compare to means, but
population (not sample) variances are employed in the calculations
- less practical test because population variances often not known
When is odds ratio close to relative risk? - CORRECT ANSWER >>>when outcome of a
casecontrol study is not common in the population
What is the null hypothesis? - CORRECT ANSWER >>>statement of no relationship between the
exposure and the outcome
What does a wide confidence interval suggest? - CORRECT ANSWER >>>small sample size and
insufficient power
increasing sample size increases the power of a study and consequently makes teh confidence
interval of the power estimate (e.g. relative risk ) tighter
What determines statistical significance in confidence interals? - CORRECT ANSWER >>>95%
confidence interval does not include the null value (1.0)
What kind of bias results from loss to follow-up in prospective studies? - CORRECT ANSWER
>>>creates potential for selection bias
How is specificity calculated? - CORRECT ANSWER >>>TN/TN+FP
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ANSWERS ALREADY GRADED A+ (BRAND NEW)
What is confounding? - CORRECT ANSWER >>>bias that can result when the exposuredisease
relationship is mixed with the effect of extraneous factors (i.e. confounders).
What is the NPV? - CORRECT ANSWER >>>probability of being free of a disease if the result is
negative
- varies wsith pretest probability
What is the purpose of randomization? - CORRECT ANSWER >>>method to control confounders
in the design stage of a study
- helps to control known risk factors as well as unknown and difficult-to-measure confounders
What is the Chi-square test? - CORRECT ANSWER >>>compares the proportions of a categorized
outcome
- ex) serum CRP level is either high or normal and is presented with the expsoure (HRT or no
HRT) in a 2x2 table.
- compared observed values with expected values
What is latent period? - CORRECT ANSWER >>>natural phenomenon (not a bias)
- infectious disease = short latency and chronic disease = long latency
- extended period of exposure may be necessary to affect outcome
- selection bias is a distortion in the estimation of exposure-disease relationship due to
inappropriate means of people selection for the study or due to selective losses from follow-
up what is susceptibility bias? - CORRECT ANSWER >>>type of selection bias where treatment
1|Page
, regiment is selected fore a patient based on the severity of their condition without taking into
account other possible confounding variables.
What is the purpose of matching cases with controls based on characteristics like age, race, etc?
- CORRECT ANSWER >>>reduce confounding variables
How is NNT calculated? - CORRECT ANSWER >>>NNT = 1/ARR
ARR = CER-EER
What is the affect of changing the cutoff value for a given condition? - CORRECT ANSWER
>>>alters the PPV, NPV, sensitivity, and specificity
- increased specificity correlates with increased PPV
- increased sensitivity corresponds to increased NPV
What is the affect of lowering the cut off point? - CORRECT ANSWER >>>increases teh
sensitivity of a test, but as a result, false positives will increase, so PPV will decrease and false
negatives will decrease
PPV= TP/TP+FP
Sensitivity = TP/TP+FN
Specificity = TN/TN+FP
How does prevalence affect PPV and NPV? - CORRECT ANSWER >>>PPV increases with an
increase in prevalence of disease in the study population
NPV decreases with increase in prevalence of disease in the study population
How is NPV calculated? - CORRECT ANSWER >>>TN/TN+FN
2|Page
, What is the two-sample t test? - CORRECT ANSWER >>>statistical method that is commonly
employed to compare the means of two groups of subjects
what is ANOVA? - CORRECT ANSWER >>>analysis of variance is used to compare three or more
means
What is the two-sample z test? - CORRECT ANSWER >>>used to compare to means, but
population (not sample) variances are employed in the calculations
- less practical test because population variances often not known
When is odds ratio close to relative risk? - CORRECT ANSWER >>>when outcome of a
casecontrol study is not common in the population
What is the null hypothesis? - CORRECT ANSWER >>>statement of no relationship between the
exposure and the outcome
What does a wide confidence interval suggest? - CORRECT ANSWER >>>small sample size and
insufficient power
increasing sample size increases the power of a study and consequently makes teh confidence
interval of the power estimate (e.g. relative risk ) tighter
What determines statistical significance in confidence interals? - CORRECT ANSWER >>>95%
confidence interval does not include the null value (1.0)
What kind of bias results from loss to follow-up in prospective studies? - CORRECT ANSWER
>>>creates potential for selection bias
How is specificity calculated? - CORRECT ANSWER >>>TN/TN+FP
3|Page
