Subjective Discretionary Income Scale: SDI (O’Guinn and Wells 1989) - Statswork

Subjective Discretionary Income Scale: SDI (O’Guinn and Wells 1989)


As originally conceptualized and developed by O'Guinn and Wells, subjective discretionary income (SDI) is a measure of perceived spending power. Specifically, it is "an estimate by the consumer of how much money he or she has to spend on nonessentials" (p. 32). As such, the SDI assesses the capacity to spend and is considered an attitudinal rather than an objective behavioral resource.


There are three components in the SDI which are:-

  • No matter how fast our income goes up we never seem to get ahead
  • We have more to spend on extras than most of our neighbors
  • Our family income is high enough to satisfy nearly all of our important desires


The SDI is a three-item scale where the items are scored on 6-point scales ranging from definitely disagree to definitely agree. Item scores are summed to form an overall SDI index that can range from 3 to 18.


Using quartile splits of the SDI, O'Guinn and Wells reported that 20.4% of their sample fell into the "low" SDI level (range of 3-6), 35.2% of their sample fell into the "medium" SDI level (range of 7-10), 32.9% of their sample fell into the "medium-high" SDI level (range of 11-14), and 11.5% of their sample fell into the "high" SDI level (range of 15-18). O'Guinn and Wells (1989) report that the SDI items had high loadings on a single factor (i.e., > .80) with item-to-total correlations ranging from .57 to .69. They report a correlation of r .34 between the SDI and total family income (TFI) as evidence of discriminant validity and, using logistic regression, show that the SDI was a significant predictor of numerous financial-based products and services (e.g., mutual funds, money market funds, and stock ownership).


O'Guinn, Thomas C , and William D. Wells. (1989). "Subjective Discretionary Income." Marketing Research: A Magazine of Application and Practice, I, 32-41.

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