Biostatistics Exam 2 questions well
answered to pass
Factors that effect the sampling distribution: - correct answer ✔✔SAMPLE DESIGN (SRS): Non random
may be biased.
SAMPLE SIZE (n): As becomes larger, sample statistic converges on true population.
VARIABILTY (SD): How quickly converges.
Sub-sample populations - correct answer ✔✔Used to find out about populations.
Sample statistics - correct answer ✔✔Used to predict population parameters.
SEM (standard error of the mean) - correct answer ✔✔One of the most commonly reported measures of
spread. Formula: SEM: SD/sqrt(n)
Xbar - correct answer ✔✔SAMPLE MEAN. Best average of mean. Xbar is unbiased. SEM describes the
VARIABILITY of Xbar. Regardless of the distribution of individuals in the population, distribution of the
sample mean (Xbar) becomes normal as n gets large. in 95% of all samples, Xbars lies within 2 SD of the
population mean. Less variable & more normal with SRS.
Central Limit Theorem - correct answer ✔✔The theory allows us to infer about mean from just 1 sample
(using Xbar, s). As n within a random sample becomes large, the sampling distribution of a statistic
becomes normal, even from a strongly non-normal population.
Unstandardizing - correct answer ✔✔Working with inverse normal distribution.
x= zs+Xbar
Confidence Intervals - correct answer ✔✔A formal way to make statements about the probable location
of a parameter from a statistic. Larger CI (smaller sample)=less certainty, SMALLER= MORE CERTAINTY.
Typically use 90% or greater. A general formula to express the confidence interval for the mean: (Mean
+/+ the standard error). (assuming SD is known):
, Xbar(mean)+/- Z*(SD/sqrt(n))
What will happen to the interval as % confidence increases? - correct answer ✔✔The interval will
increase.
Standardizing - correct answer ✔✔All normal curves are the same if we measure them in units of size
(SD) about the mean. A standardized value is a "z-score".
Standard normal curve: mean=0 & SD=1
(POPULATION): (x-mean)/SD
(SAMPLE): z= (x-xbar)/s
Degrees of freedom - correct answer ✔✔Number of samples minus 1 (n-1).
Null hypothesis (Ho) - correct answer ✔✔Test designed to assess the strength of the evidence against
the null hypothesis. A claim about a population characteristic that is initially asummed to be true. State
in terms of "no effect" or "no difference". Will always be an equality: (u=uo).
3 forms: u>uo, u<uo, u(not)=uo.
Alternative hypothesis (Ha) - correct answer ✔✔Claim about population that we are trying to find
evidence for. The statement that the parameter has a value that differs from the null hypothesis. One-
sided if it states that a parameter is larger than or smaller than the null hypothesis value. Two-sided if it
states that the parameter is different from the null value (smaller or larger).
Hypothesis - correct answer ✔✔A claim or statement about either the value of a single population
characteristic or the values of several population characteristics.
Hypothesis test (test of significance) - correct answer ✔✔A procedure for using sample data to decide
between 2 competing claims (hypotheses) about a population characteristic.
One-tailed hypothesis tests - correct answer ✔✔One-sided, directional. a is placed under one tail.
answered to pass
Factors that effect the sampling distribution: - correct answer ✔✔SAMPLE DESIGN (SRS): Non random
may be biased.
SAMPLE SIZE (n): As becomes larger, sample statistic converges on true population.
VARIABILTY (SD): How quickly converges.
Sub-sample populations - correct answer ✔✔Used to find out about populations.
Sample statistics - correct answer ✔✔Used to predict population parameters.
SEM (standard error of the mean) - correct answer ✔✔One of the most commonly reported measures of
spread. Formula: SEM: SD/sqrt(n)
Xbar - correct answer ✔✔SAMPLE MEAN. Best average of mean. Xbar is unbiased. SEM describes the
VARIABILITY of Xbar. Regardless of the distribution of individuals in the population, distribution of the
sample mean (Xbar) becomes normal as n gets large. in 95% of all samples, Xbars lies within 2 SD of the
population mean. Less variable & more normal with SRS.
Central Limit Theorem - correct answer ✔✔The theory allows us to infer about mean from just 1 sample
(using Xbar, s). As n within a random sample becomes large, the sampling distribution of a statistic
becomes normal, even from a strongly non-normal population.
Unstandardizing - correct answer ✔✔Working with inverse normal distribution.
x= zs+Xbar
Confidence Intervals - correct answer ✔✔A formal way to make statements about the probable location
of a parameter from a statistic. Larger CI (smaller sample)=less certainty, SMALLER= MORE CERTAINTY.
Typically use 90% or greater. A general formula to express the confidence interval for the mean: (Mean
+/+ the standard error). (assuming SD is known):
, Xbar(mean)+/- Z*(SD/sqrt(n))
What will happen to the interval as % confidence increases? - correct answer ✔✔The interval will
increase.
Standardizing - correct answer ✔✔All normal curves are the same if we measure them in units of size
(SD) about the mean. A standardized value is a "z-score".
Standard normal curve: mean=0 & SD=1
(POPULATION): (x-mean)/SD
(SAMPLE): z= (x-xbar)/s
Degrees of freedom - correct answer ✔✔Number of samples minus 1 (n-1).
Null hypothesis (Ho) - correct answer ✔✔Test designed to assess the strength of the evidence against
the null hypothesis. A claim about a population characteristic that is initially asummed to be true. State
in terms of "no effect" or "no difference". Will always be an equality: (u=uo).
3 forms: u>uo, u<uo, u(not)=uo.
Alternative hypothesis (Ha) - correct answer ✔✔Claim about population that we are trying to find
evidence for. The statement that the parameter has a value that differs from the null hypothesis. One-
sided if it states that a parameter is larger than or smaller than the null hypothesis value. Two-sided if it
states that the parameter is different from the null value (smaller or larger).
Hypothesis - correct answer ✔✔A claim or statement about either the value of a single population
characteristic or the values of several population characteristics.
Hypothesis test (test of significance) - correct answer ✔✔A procedure for using sample data to decide
between 2 competing claims (hypotheses) about a population characteristic.
One-tailed hypothesis tests - correct answer ✔✔One-sided, directional. a is placed under one tail.
