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How might asymmetry arise in data?
When there is a constraint at the other end of the distribution
This can be natural (number of values on a dice) or man made (difficulty of a test)
What is the ceiling effect?
The test is too easy
Causes negative skew as more people do well
What is the floor effect?
The test is too hard
Causes a positive skew as fewer people do well
What is symmetrical distribution
The normal distribution of data for a typical sample group
What is bimodality?
The presence of two peaks in a distribution
Usually indicates that the measuring instrument is dividing data into two distinct subgroups
(scores on memory tests when some have eidetic memories)
What is the correlation coefficient?
An index of the linear relationship between two values
Must fall between +1 (perfect positive correlation) and -1 (perfect negative correlation)
0.0 implies no linear relationship (but possibly a non linear one)
What is the modal value?
The most frequently appearing score in a data set
What is the modal class?
The class interval containing the highest frequency of quantitative scores
What is the modal category?
The category with the highest frequency of counts (categorical)