the good, the bad, and the ugly: blazing trails with z-scoringthe good, the bad, and the ugly-...
TRANSCRIPT
The Good, The Bad, and The Ugly- Blazing Trails
with Z-scoring2013 IPAC
Session Agenda
• Introduction- presentation context- presenter bio and organizational experience with z-scoring
• Segment 1- Z-scoring defined and illustrated using Excel• Segment 2- The Good: Reasons/rationales for z-scoring• Segment 3- The Bad: Challenges in using z-scoring• Segment 4- The Ugly: Z-scoring sour grapes and such• Discussion
Presentation Context
• Presenter bio- business degree, 23 years with City of Columbus, 6 years as accountant, 17 years as personnel analyst
• City of Columbus Civil Service employment testing, z-scoring late 70s, early 80s
• Safety forces testing, entry level and promotional; non-uniformed
Z-scoring Defined
The standard normal curve (aka the bell curve)
Properties of the Distribution
• Mean is 0 (center of the scale)
• Standard Deviation is 1
• 99.6% of the data should fall within + or – 3 standard deviations
Practical ImplicationWhen it comes to test scores, if our test is valid we can infer that the likelihood of a candidate being successful at the job increases as we move from left to right along the z-score spectrum, and that significantly higher z-scores should translate to higher or better performance.
Z-score formula:
• Population standard deviation vs. sample standard deviation
Calculating Z-scores using Excel
• Organize the data (columns?)
• Use functions-
AVERAGE, STDEVP
• Absolute vs Relative cell referencing
• Sample score data transformed to z-scores
The Good:• Allows the establishment of a passpoint based
on group performance rather than a fixed score
• Mitigates potential effects of “difficult” or “easy” exams
• Mitigates potential dilution of performance resulting from multiple phases having significantly different levels of variance
The Good (cont’d):
• Enables proper weighting
• Ensures seniority points have a consistent “meaningfulness” from test to test
The Bad:• Can be difficult for candidates to understand
• Can undermine trust in process
• Can have some unintended effects
The Ugly:• Police Commander anecdote
• Accountant I anecdote
• Police candidate forum
• Audience anecdotes?
