CPH EXAM-BIOSTATISTICS EXAM COMPLETE
QUESTIONS AND CORRECT ANSWERS 2023-202
Biostatistics includes a set of principles and methods which allow us to ,
and important public health problems. - Answer assess, analyze
andsolve
The application of biostatistics involves what? - Answer The application of
biostatistics involves developing clear research questions, designing studies to
collect relevant information or data, applying appropriate techniques to analyze those
data and drawingmeaningful conclusions from data appropriately accounting for
uncertainty.
T/F: In every study, it is not important to define the population of interest. -
AnswerFalse
T/F: The population is the collection of all units (usually people) that we wish to make
inferences about. The appropriate population depends on the research question. -
Answer True
T/F: Using a probability sampling technique maximizes the likelihood the sample
isrepresentative of the larger population. - Answer True
T/F: This is important to minimize bias which is a systematic error in a study that
leads to uncertainty about the estimates generated from the study. Bias is actually
caused bythe investigators in the design or conduct of the study - Answer True
Summary measures based on population data are called and estimates
derived from sample data are called . - Answer Summary measures based
onpopulation data are called parameters and estimates derived from sample data
are called statistics.
N is used to denote the and is an example of a parameter, n denotes the
and is an example of a statistic - Answer N is used to denote the
population size and is an example of a parameter, n denotes the sample size and is
an example ofa statistic.
T/F: In applied biostatistical analysis, we use sample statistics to estimate
unknownpopulation parameters. - Answer True
Name three general classifications of variables - Answer discrete, continuous and
timeto event variables
,Discrete variables - Answer variables that assume only a finite number of values, for
example, whether or not a participant is taking lipid lowering treatment (yes or no), their
blood type (A, B, AB or O), or symptom severity (none, mild, moderate, or severe).
Discrete variables with two response options are called -
AnswerDiscrete variables with two response options are called dichotomous
Discrete variables with more than 2 unordered are called -
AnswerDiscrete variables with more than 2 unordered are called
categorical/nominal
Continuous variables - Answer Sometimes called quantitative or measurement
variables, can take on any value within a range of plausible values. For example,
total serum cholesterol level, height, weight and systolic blood pressure are examples
of continuous variables. Time to event variables reflect the time to a particular event
suchas a heart attack, cancer remission or death.
Ordered response options are called - Answer Ordered response
optionsare called ordinal variables
Continuous variables are summarized using measures of and
. - Answer Continuous variables are summarized using measures
ofcentral tendency and variability
The and are generally appropriate to describe central
tendency and variability, respectively. - Answer The mean and standard deviation
are generallyappropriate to describe central tendency and variability, respectively.
The mean is computed: - Answer n = the sample size or the number of participants
inthe sample
The standard deviation is computed as follows: - Answer
T/F: When there are extreme values in the sample (called outliers), the mean may be
inflated or deflated depending on whether the extreme values are high or low. - Answer
True
When there are outliers, what ranges are appropriate to describe central tendency
andvariability, respectively? - Answer When there are outliers, the median (middle
value) and interquartile range (third quartile, Q3, 75th percentile - first quartile, Q1,
25th percentile) are appropriate to describe central tendency and variability,
respectively.
Popular guide for assessing outliers: - Answer Outliers are values either above
Q3+1.5(Q3-Q1) or below Q1-1.5(Q3-Q1), where Q1 and Q3 are the first and
thirdquartiles, respectively.
,T/F: A box and whisker plot is a popular graphical display for a continuous variable -
Answer True: The "box" contains the middle 50% of the distribution (i.e., Q1 is the
bottom of the box and Q3 is the top of the box) and the median is the horizontal line
inbetween. The range of the data (minimum to maximum) are indicated by the
vertical line. Some computer packages will indicate outliers in the sample in the box
and whisker plot.
When comparing groups with respect to a continuous variable, we typically compare
the
between groups. - Answer When comparing groups with respect to
acontinuous variable, we typically compare the means between groups.
What do µ1 and µ2 represent? - Answer Let µ1 and µ2 be the true, unknown population
means of the two groups that we wish to compare.
How is the difference in the true means (µ1- µ2) estimated? - Answer The difference
in the true means (µ1- µ2) is estimated by the difference in the observed sample
means (X1-X2 ).
Categorical and ordinal variables are best summarized by the and
proportionor of participants in each response category. - Answer Categorical
and ordinal variables are best summarized by the frequency (count) and proportion or
relative frequency (frequency/n) of participants in each response category.
T/F: Graphical displays are also useful for summarizing discrete data. - Answer True
What type of chart is used to summarize categorical or nominal variable? - Answer A
bar chart is used to summarize a categorical or nominal variable
What type of chart is used to summarize ordinal data? - Answer A histogram is used
tosummarize ordinal data
What do p1 and p2 represent? - Answer Let p1 and p2 be the true, unknown
populationproportions in the two groups that we wish to compare.
How is the difference in the true proportions (p1-p2) estimated? - Answer The
differencein the true proportions (p1-p2) is estimated by the difference in the observed
sample proportions.
Also called the risk difference
Relative Risk Ratio: - Answer Estimated using the observed sample data.
, Odds ratio: - Answer Estimated using the observed sample data.
T/F: relative risk ratio is more intuitive - Answer True
T/F: in case-control studies, it is not possible to estimate a relative risk because the
case-control design involves selecting participants on the basis of their outcome
status.
- Answer True
T/F: in case-control studies, the odds ratio can be estimated and used to summarize
theassociation between the exposure or risk factor and the outcome. - Answer True
T/F: When the proportion of outcome events is low, the odds ratio is close in value
tothe relative risk. - Answer True
A common way to summarize time to event data is through a - Answer
Acommon way to summarize time to event data is through a hazard rate
What is the hazard rate? - Answer The hazard rate is the rate of a particular
outcome conditional on time. To compare two groups with respect to the time to
event, we usethe hazard ratio, which is the ratio of the hazard rates for each group.
What is a probability? - Answer A probability is a number between 0 and 1
(inclusive)that represents the likelihood that a particular outcome occurs.
A random variable is a variable whose value is determined by . - Answer
Arandom variable is a variable whose value is determined by chance.
T/F: A probability distribution is a table or a function that links each value of a
randomvariable to its likelihood of occurring (probability). - Answer True
The normal distribution is characterized by its and .-
AnswerThe normal distribution is characterized by its mean and standard
deviation.
A normal distribution is one in which the mean is equal to the (and also
to the mode or the most frequent value). - Answer A normal distribution is one in
which themean is equal to the median (and also to the mode or the most frequent
value).
Approximately 95% of the values in a normal distribution lie between the mean minus
times the standard deviation and the mean plus times the standard
deviation. - Answer Approximately 95% of the values in a normal distribution lie
between the mean minus two times the standard deviation and the mean plus two
timesthe standard deviation.
QUESTIONS AND CORRECT ANSWERS 2023-202
Biostatistics includes a set of principles and methods which allow us to ,
and important public health problems. - Answer assess, analyze
andsolve
The application of biostatistics involves what? - Answer The application of
biostatistics involves developing clear research questions, designing studies to
collect relevant information or data, applying appropriate techniques to analyze those
data and drawingmeaningful conclusions from data appropriately accounting for
uncertainty.
T/F: In every study, it is not important to define the population of interest. -
AnswerFalse
T/F: The population is the collection of all units (usually people) that we wish to make
inferences about. The appropriate population depends on the research question. -
Answer True
T/F: Using a probability sampling technique maximizes the likelihood the sample
isrepresentative of the larger population. - Answer True
T/F: This is important to minimize bias which is a systematic error in a study that
leads to uncertainty about the estimates generated from the study. Bias is actually
caused bythe investigators in the design or conduct of the study - Answer True
Summary measures based on population data are called and estimates
derived from sample data are called . - Answer Summary measures based
onpopulation data are called parameters and estimates derived from sample data
are called statistics.
N is used to denote the and is an example of a parameter, n denotes the
and is an example of a statistic - Answer N is used to denote the
population size and is an example of a parameter, n denotes the sample size and is
an example ofa statistic.
T/F: In applied biostatistical analysis, we use sample statistics to estimate
unknownpopulation parameters. - Answer True
Name three general classifications of variables - Answer discrete, continuous and
timeto event variables
,Discrete variables - Answer variables that assume only a finite number of values, for
example, whether or not a participant is taking lipid lowering treatment (yes or no), their
blood type (A, B, AB or O), or symptom severity (none, mild, moderate, or severe).
Discrete variables with two response options are called -
AnswerDiscrete variables with two response options are called dichotomous
Discrete variables with more than 2 unordered are called -
AnswerDiscrete variables with more than 2 unordered are called
categorical/nominal
Continuous variables - Answer Sometimes called quantitative or measurement
variables, can take on any value within a range of plausible values. For example,
total serum cholesterol level, height, weight and systolic blood pressure are examples
of continuous variables. Time to event variables reflect the time to a particular event
suchas a heart attack, cancer remission or death.
Ordered response options are called - Answer Ordered response
optionsare called ordinal variables
Continuous variables are summarized using measures of and
. - Answer Continuous variables are summarized using measures
ofcentral tendency and variability
The and are generally appropriate to describe central
tendency and variability, respectively. - Answer The mean and standard deviation
are generallyappropriate to describe central tendency and variability, respectively.
The mean is computed: - Answer n = the sample size or the number of participants
inthe sample
The standard deviation is computed as follows: - Answer
T/F: When there are extreme values in the sample (called outliers), the mean may be
inflated or deflated depending on whether the extreme values are high or low. - Answer
True
When there are outliers, what ranges are appropriate to describe central tendency
andvariability, respectively? - Answer When there are outliers, the median (middle
value) and interquartile range (third quartile, Q3, 75th percentile - first quartile, Q1,
25th percentile) are appropriate to describe central tendency and variability,
respectively.
Popular guide for assessing outliers: - Answer Outliers are values either above
Q3+1.5(Q3-Q1) or below Q1-1.5(Q3-Q1), where Q1 and Q3 are the first and
thirdquartiles, respectively.
,T/F: A box and whisker plot is a popular graphical display for a continuous variable -
Answer True: The "box" contains the middle 50% of the distribution (i.e., Q1 is the
bottom of the box and Q3 is the top of the box) and the median is the horizontal line
inbetween. The range of the data (minimum to maximum) are indicated by the
vertical line. Some computer packages will indicate outliers in the sample in the box
and whisker plot.
When comparing groups with respect to a continuous variable, we typically compare
the
between groups. - Answer When comparing groups with respect to
acontinuous variable, we typically compare the means between groups.
What do µ1 and µ2 represent? - Answer Let µ1 and µ2 be the true, unknown population
means of the two groups that we wish to compare.
How is the difference in the true means (µ1- µ2) estimated? - Answer The difference
in the true means (µ1- µ2) is estimated by the difference in the observed sample
means (X1-X2 ).
Categorical and ordinal variables are best summarized by the and
proportionor of participants in each response category. - Answer Categorical
and ordinal variables are best summarized by the frequency (count) and proportion or
relative frequency (frequency/n) of participants in each response category.
T/F: Graphical displays are also useful for summarizing discrete data. - Answer True
What type of chart is used to summarize categorical or nominal variable? - Answer A
bar chart is used to summarize a categorical or nominal variable
What type of chart is used to summarize ordinal data? - Answer A histogram is used
tosummarize ordinal data
What do p1 and p2 represent? - Answer Let p1 and p2 be the true, unknown
populationproportions in the two groups that we wish to compare.
How is the difference in the true proportions (p1-p2) estimated? - Answer The
differencein the true proportions (p1-p2) is estimated by the difference in the observed
sample proportions.
Also called the risk difference
Relative Risk Ratio: - Answer Estimated using the observed sample data.
, Odds ratio: - Answer Estimated using the observed sample data.
T/F: relative risk ratio is more intuitive - Answer True
T/F: in case-control studies, it is not possible to estimate a relative risk because the
case-control design involves selecting participants on the basis of their outcome
status.
- Answer True
T/F: in case-control studies, the odds ratio can be estimated and used to summarize
theassociation between the exposure or risk factor and the outcome. - Answer True
T/F: When the proportion of outcome events is low, the odds ratio is close in value
tothe relative risk. - Answer True
A common way to summarize time to event data is through a - Answer
Acommon way to summarize time to event data is through a hazard rate
What is the hazard rate? - Answer The hazard rate is the rate of a particular
outcome conditional on time. To compare two groups with respect to the time to
event, we usethe hazard ratio, which is the ratio of the hazard rates for each group.
What is a probability? - Answer A probability is a number between 0 and 1
(inclusive)that represents the likelihood that a particular outcome occurs.
A random variable is a variable whose value is determined by . - Answer
Arandom variable is a variable whose value is determined by chance.
T/F: A probability distribution is a table or a function that links each value of a
randomvariable to its likelihood of occurring (probability). - Answer True
The normal distribution is characterized by its and .-
AnswerThe normal distribution is characterized by its mean and standard
deviation.
A normal distribution is one in which the mean is equal to the (and also
to the mode or the most frequent value). - Answer A normal distribution is one in
which themean is equal to the median (and also to the mode or the most frequent
value).
Approximately 95% of the values in a normal distribution lie between the mean minus
times the standard deviation and the mean plus times the standard
deviation. - Answer Approximately 95% of the values in a normal distribution lie
between the mean minus two times the standard deviation and the mean plus two
timesthe standard deviation.
