Biostatistics
What are 2 broad areas into which statistical methods fall? – answer
1. Descriptive statistics
2. Inferential statistics
What is the purpose of descriptive statistics? - answer describe, organize, or summarize data:
refer only to the actual data available
What is an example of descriptive statistics? - answer mean blood pressure of a group
success rate of a surgical procedure
What is the purpose of inferential statistics? - answer making inferences that go beyond the
actual data:
Usually involve inductive reasoning
What is an example of inferential statistics? - answer- mean blood pressure of all Americans
- expected success rate of a surgical pocedure in patients who have not yet undergone the
operation
What is a population? – answer the universe about which an investigator wishes to draw
conclusions
Does a population need to consist of people? – answer no
What is a sample – answer subset of the population- the part that is being observed or studied
What is an element? - answer a single observation, denoted by X
The number of elements in a population is denoted by what? – answer N
The number of elements in a sample is denoted by what? – answer n
What does a population consist of? – answer all elements from X1 to XN
What does a sample consist of? – answer n of N elements
Most samples used in biomedical research are what? - answer probability samples
What are probability samples? - answer samples in which the researcher can specify the
probability of any one element in the population being included
Probability samples permit the use of what type of statistics? - answer inferential statistics
,Nonprobability samples allow what type of statistics to be used? – answer descriptive statistics
only
What are the four basic kinds of probability samples? – answer
1. Simple random samples
2. Stratified random samples
3. Cluster samples
4. Systematic samples
What is the simplest kind of probability sample? - answer simple random sample
How is a simple random sample drawn? - answer in such a way that every element in the
population has an equal probability of being included
A random sample is defined by what? - answer the method of drawing the sample, not by the
outcome
When is a sample representative? - answer if it closely resembles the population from which it is
drawn
When does a sample or result demonstrate bias? - answer if it consistently errs in a particular
direction
Are biased samples representative? - answer no, they are unrepresentative. true randomization is
proof against bias
What happens in a stratified random sample? - answer the population is first divided into
relatively internally homogenous groups, or strata, from which random samples are then drawn.
When are cluster samples used? - answer when it is too expensive or laborious to draw a simple
random sample or stratified random sample
How is a cluster sample drawn? - answer an investigator starts by selecting a random set of
clusters and then selecting a subset of each.
How are systematic samples drawn? - answer selecting elements in a systematic way (i.e. every
5th one)
What advantage do systematic samples provide? - answer the equivalent of a simple random
sample without actually using randomization
What is a common sampling problem in clinical research? – answer self-selection
What is internal validity? - answer when a study is valid as far as a subset of patients are
concerned
, What is external validity? - answer being valid to generalize a study to an entire population
extrapolated from a sample
The probability of an event is denoted by what? – answer p
How are probabilities expressed? - answer decimal fractions between 0-1
Can the probability of an event be negative? - answer no
The probability of an event not occurring is equal to what? – answer q=1-p
What is the addition rule of probability? - answer the probability of any one of several particular
events occurring is equal to the sum of their individual probabilities, provided the events are
mutually exclusive
What is the multiplication rule of probability? - answer the probability of two or more
statistically independent events all occurring is equal to the product of their individual
probabilities
The probability that a specific combination of mutually exclusive independent evens will occur
can be determined by what? - answer binomial distribution
What is a binomial distribution? - answer one in which there are only two possibilities, such as
yes/no. the binomial distribution gives the probability of obtaining an exact number of successes
in a series of independent trials.
What is a typical medical use of the binomial distribution? - answer genetic counseling
What are the four scales of measurement? – answer
1. Nominal
2. Ordinal
3. Interval
4. Ratio
What are nominal scale data? - answer data divided into qualitative categories or groups
Is there implication of order or ratio for nominal scale data? - answer no
What are nominal data that fall into only two groups called? - answer dichotomous data
What are ordinal scale data? - answer data that can be placed in a meaningful order, but lacks
information about the size of the interval
What are interval scale data? - answer data that can be placed in a meaningful order and have
meaningful intervals between items, which are usually measured quantities.
What are 2 broad areas into which statistical methods fall? – answer
1. Descriptive statistics
2. Inferential statistics
What is the purpose of descriptive statistics? - answer describe, organize, or summarize data:
refer only to the actual data available
What is an example of descriptive statistics? - answer mean blood pressure of a group
success rate of a surgical procedure
What is the purpose of inferential statistics? - answer making inferences that go beyond the
actual data:
Usually involve inductive reasoning
What is an example of inferential statistics? - answer- mean blood pressure of all Americans
- expected success rate of a surgical pocedure in patients who have not yet undergone the
operation
What is a population? – answer the universe about which an investigator wishes to draw
conclusions
Does a population need to consist of people? – answer no
What is a sample – answer subset of the population- the part that is being observed or studied
What is an element? - answer a single observation, denoted by X
The number of elements in a population is denoted by what? – answer N
The number of elements in a sample is denoted by what? – answer n
What does a population consist of? – answer all elements from X1 to XN
What does a sample consist of? – answer n of N elements
Most samples used in biomedical research are what? - answer probability samples
What are probability samples? - answer samples in which the researcher can specify the
probability of any one element in the population being included
Probability samples permit the use of what type of statistics? - answer inferential statistics
,Nonprobability samples allow what type of statistics to be used? – answer descriptive statistics
only
What are the four basic kinds of probability samples? – answer
1. Simple random samples
2. Stratified random samples
3. Cluster samples
4. Systematic samples
What is the simplest kind of probability sample? - answer simple random sample
How is a simple random sample drawn? - answer in such a way that every element in the
population has an equal probability of being included
A random sample is defined by what? - answer the method of drawing the sample, not by the
outcome
When is a sample representative? - answer if it closely resembles the population from which it is
drawn
When does a sample or result demonstrate bias? - answer if it consistently errs in a particular
direction
Are biased samples representative? - answer no, they are unrepresentative. true randomization is
proof against bias
What happens in a stratified random sample? - answer the population is first divided into
relatively internally homogenous groups, or strata, from which random samples are then drawn.
When are cluster samples used? - answer when it is too expensive or laborious to draw a simple
random sample or stratified random sample
How is a cluster sample drawn? - answer an investigator starts by selecting a random set of
clusters and then selecting a subset of each.
How are systematic samples drawn? - answer selecting elements in a systematic way (i.e. every
5th one)
What advantage do systematic samples provide? - answer the equivalent of a simple random
sample without actually using randomization
What is a common sampling problem in clinical research? – answer self-selection
What is internal validity? - answer when a study is valid as far as a subset of patients are
concerned
, What is external validity? - answer being valid to generalize a study to an entire population
extrapolated from a sample
The probability of an event is denoted by what? – answer p
How are probabilities expressed? - answer decimal fractions between 0-1
Can the probability of an event be negative? - answer no
The probability of an event not occurring is equal to what? – answer q=1-p
What is the addition rule of probability? - answer the probability of any one of several particular
events occurring is equal to the sum of their individual probabilities, provided the events are
mutually exclusive
What is the multiplication rule of probability? - answer the probability of two or more
statistically independent events all occurring is equal to the product of their individual
probabilities
The probability that a specific combination of mutually exclusive independent evens will occur
can be determined by what? - answer binomial distribution
What is a binomial distribution? - answer one in which there are only two possibilities, such as
yes/no. the binomial distribution gives the probability of obtaining an exact number of successes
in a series of independent trials.
What is a typical medical use of the binomial distribution? - answer genetic counseling
What are the four scales of measurement? – answer
1. Nominal
2. Ordinal
3. Interval
4. Ratio
What are nominal scale data? - answer data divided into qualitative categories or groups
Is there implication of order or ratio for nominal scale data? - answer no
What are nominal data that fall into only two groups called? - answer dichotomous data
What are ordinal scale data? - answer data that can be placed in a meaningful order, but lacks
information about the size of the interval
What are interval scale data? - answer data that can be placed in a meaningful order and have
meaningful intervals between items, which are usually measured quantities.
