Presentation of Data Flashcards
Why do you screen data?
To detect blunders
To locate outliers
Distributional properties
Missing values
What are the 2 types of measurement?
Qualitative - nominal or ordinal
Quantitative - interval
Describe groups of qualitative data:
Nominal - non ordered e.g male or female
Ordinal - ordered e.g pain levels
What is frequency distribution?
Shows the frequency (or count) of the occurrence of different values of a variable
What is relative frequency?
The frequency expressed as a proportion (or percentage) of the total frequency
How are interval scale variables graphically presented?
Histogram -
Box plots
Define;
mean
median
mode
Mean -
Median - middle value if a sample is arranged in increasing order
Mode -
What are summary statistics used for?
Attempt to capture a typical value (the location) or the spread (or dispersion).
What is range and why is not used to detect dispersion?
The range is the difference between the largest and smallest observations in the sample;
Not recommended as it is severely affected by outlying observations.
What is variance?
The variance (s2) is the sum of the squared distance of each value from the mean, divided by the number of values minus 1
Basically how far a result is from the mean
What is standard deviation and why does it have presence over variation?
Square root of the variance.
Advantage of being in the original scale of measurement, and is therefore used in preference to the variance
What is the coefficient of variation?
Provides a measure of variation which is independent of the unit of measurement
Used to compare the variation of variables measured on different scales
What summary statistics are used for roughly symmetrical distribution?
The mean and standard deviation
What summary statistics are used for skewed distribution?
Median and interquartile range
