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?

General Discussion or Questions?

Michael Maloney mmaloney1@columbus.gov 614-645-7494