# 1 Biostatistics

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2016-06-02 17:01

Question | Answer |
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Children or elder abuse | broken ribs, subdural hematoma and bilateral bruises on arms |

Hardy–Weinberg law | allele frequencies: p+q=1 a gene that exists in two alleles, gene frequencies (p2) + (2pq) + (q2) = 1 x linked recessive mutation, male=q, femaile =q2 KA23-11, KA12/6, KA36-4 |

steady state concentraton | continuous infusion at a dose of 0.1 mg/min half life is 1.9 hours volume of distribution is 230 L The clearance is 60L/h (=1L/min) the steady-state concentration=0.1/1=0.1 KA12/18 |

volume of distribution | Vd= volume=the ratio of the dose and its plasma concentration Drugs with a smll Vd: too large, binds to albumin, low lipid solubility t1/2=(0.7x Vd)/CL Vd=(the clearance x half life)/0.7 |

lower incidence of cancer | new vaccine, decreased risk factors can lower incidence new treatment, early detection can lower prevalence (no change on incidence) increased survival can increase prevalence (no change on incidence) increased death from disease can lower prevalence (no change on incidence) |

which of substrate con.c is most suitable for conducitng the desired enzyme assay? | use con.c when the reaction rate approaches Vmax>>>the rate will vary in proportion to changes in enzyme con.c. the substrate con.c is in the range of first order kinetics with respect to substrate. the rate of the reaction will depend on both substrate and enzyme |

What does the Chi-square test? | checks difference between 2 or more percentages or proportions of categorical outcomes (NOT MEAN VALUES) |

What means an absolute value of person's correlation coefficient (r) of 1 | closer to 1= stronger the linear correlation between the 2 variables (coefficient of determination= r^2) |

What does the ANOVA test? | checks difference between the means of 3 or more groups (mnemonic: ANOVA= analysis Of Variance of 3 or more groups) |

% of sample on one SD, Two SD and three SD | 68%, 95% and 99.7% |

Question | Answer |
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What is a selection bias? | when the subject chooses whether to enter a drug group or a placebo group rather than being randomly assigned or investigator purposely chosses KA34-38 |

What is a sampling bias? | non random sample of a populatin |

What is a confounding bias? | occurs when factor is related to both exposure and outcome. Gender ,smoking status, age and race |

Question | Answer |
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What means a null statistical hypothesis (Ho)? | no difference between the disease and risk factor |

What means a alternative statistical hypothesis (H1)? | some difference |

What is a type 1 error (α) | stating difference when none exists "α: you sαw a difference that didn't exist" p<0.5; less than a 5% chance that the data will show something that is not really there |

What is a type 2 error (β)? | stating no difference when one exists "you were βlind to a difference that did exist" |

What means the power (1-β) of a result? | probability of rejecting a false null hypothesis |

What increases the power of a result? | increase sample size, increase expected effect size and increase precision of measurement |

20% probability there is no difference in blood cholesterol level when there is one in reality, what is the power of the study? | 0.8 |

Question | Answer |
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In what type of studies do we use odds ratio (OR)? | often used in case-control studies, OR=(a*d)/(b*c) case control: disease>>>risk factor |

In what type of studies do we use relative risk (RR)? | typically used in cohort studies. RR= (a/(a+b))/(c/(c+d)) cohort: risk factor >>>incidence of disease |

attributable risk | the difference in risk between exposed and unexposed groups attributable risk = (a/(a+b)) - (c/(c+d)) |

8% of people who receive a placebo vaccine develop flu vs 2% of people who receive a flu vaccine. | ARR=8%-2%=6% |

number needed to treat | Number of patients who need to be treat for 1 patient to benefit. NNT=1/ARR |

number needed to harm | Number of patients who need to be exposed to a risk for 1 patient to be harmed. NNH=1/attributable risk |

crossover study | patients serve as their own controls |

cross sectional study | what is happening? simultaneously measures exposure and outcome |

case series | people have the same condition, no control group KA34-18 |

new cases/total population AT RISK | Incidence |

No. of persons with the disease/total population | Prevalence |

a new serologic test for detecting prostate cancer is negative in 95% of patients who do not have the disease. if the test is used on 8 blood samples taken from patients without prostate cancer. What is the probability of getting at least 1 positive test result? | 1-0.95'8 |

Absolute risk reduction for drug A versus standard is 4%, incidence of pulmonary embolism with standard is 6%, and 24 pulmonary embolism in the drug group, how many total subjects are there in the drug group? | 1200 |

Question | Answer |
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confidence interval (CI) | range of values in which a specified probability of the mean of repeated samples would be expected to fall |

95% CI for a mean difference between 2 variables includes 0? | no significant difference and Ho is not rejected |

95% CI for a odds ratio or relative risk includes 1? | Ho is not rejected |

CIs between two groups don't overlap? | a significant difference exists |

Sensitivity | 1- false-negative rate |

Specificity | 1- false-positive rate |

positive predictive value (PPV)? | test(+)>>>result(+) proportion of positive test results that are true positive, =TP/(TP+FP) high prevalence>>>High PPV |

negative predictive value (NPV)? | test(-)>>>results (-) proportion of negative test result that are true negative = TN/(FN+TN) high prevalence>>>low NPV KA23-35 |

Question | Answer |
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apgar score | appearance, pulse, grimace, activity Respiration a: blue, trunk pink, pink p: 0, <100, >100 g: none, grimace, cough a:limp, some, active r: none, irregular, regular |

sleep stage | stage 3-4: Deepest non REM sleep delta (lowest frequency and highest amplitude) night terrors, bedwetting, sleepwalking stage 1 light sleep theta REM increased pulse, BP ACh increased REM and early morning awakening in depressed patients beta (highest frequency and lowest amplitude) |

Narcolepsy treatment | amphetamines, modafinil and sodium oxybate(GHB). |

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