Exam #1: Biostatistics I Flashcards
What are the six major reasons to study stats as a medical student?
1) To evaluate medical lit.
2) To communicate w/ patients
3) To communicate w/ peers
4) To evaluate your performance
5) To protect your practice from the MISuse of statistics
6) Conduct your own investigation
Where the two major divisions of the field of statistics?
- Descriptive
- Inferential
What is the purpose of descriptive statistics & what does the field involve?
Purpose is to describe data, which involves:
- collecting data
- presenting data
- characterizing data
What is the purpose of inferential statistics & what does the field involve?
Purpose is to make decisions about population characteristics, which involves:
- Estimation
- Hypothesis testing
****This field uses the descriptive stats to make generalizations about the underlying population
What are experimental elements or units of analysis?
Objects upon which we collect data
What is the population?
All of the items of interest
*****Measurements that are based on a population are called “parameters.”
What is a variable?
Characteristic of an individual experimental unit
What is a sample?
Subset of the units of a population
******Measurements that are based on a sample are called “statistics.”
What is the difference between a categorical & quantitative variable?
Categorical= a numeric or character code that represents
- Presence or absence of trait
- Relative weight/ rank of thing being studied
Quantitative= numerical result of some measurement
What are the four scales of measurement?
1) Nominal scale*
2) Ordinal scale*
3) Interval scale**
4) Ratio**
*Categorical
**Quantitative
What is the nominal scale?
Categories observations e.g. male v.s. female
What is the ordinal scale?
Nominal variables that have an order or rank e.g. cancer stage
What is an interval scale?
Measurable difference between two observations e.g. temperature
What is a ratio?
Same as interval but with an absolute reference point
How are qualitative variables described/ presented?
Summary tables/ graphs
How are quantitative variables described/ presented?
- Dot plot
- Stem & leaf display
- Frequency distribution
- Histogram
What is a class?
One of the categories into which qualitative data can be classified
What is the class frequency?
Number of observations in the data set falling into a particular class
What is the class relative frequency?
Frequency/ Total Observations
What is the class percentage?
Class relative frequency x 100
What is the difference between a bar graph and a histogram?
Bar graph= qualitative
Histogram= quantitative
What is central tendency?
Tendency of the data to cluster or center about certain numerical values
What is variability?
The spread of the data
Write the symbols for mean for both sample and a population.
Write the symbols for size for both sample and population.
What is the difference between mean, median & mode?
Mean= average
Median= central # in data set
Mode= most commonly occuring
Which measure of central tendency is most affected by extreme values?
Mean
What measures of central tendency are NOT affected by extreme values?
Median & Mode
For a data set, it is possible to NOT have a mode?
Yes, if one value does not occur more frequency than the others
For a data set can there be more than one mode?
Yes, if two numbers occur with equal frequency, then there are two modes
Draw the standard notation for standard deviation & variance for samples & populations.
What is the only numerical summary value that can be used for qualitative data?
Mode
What is the range?
Total spread of data
What is the standard deviation?
Dispersion about a mean
What is the variance?
Squared dispersion about a mean
What is the relationship between mean & median when a data set is symmetric? Left-skewed? Right-skewed?
Symmetric= equal Left= Mean median
What type of distribution must there be to apply the empirical rule?
Normal distribution
What is the empirical rule?
68%= within 1 Std
95%= within 2 Std
99.7%= within 3 Std
