IRD Calculator
clear all


removed from A
removed from B

supplemental output

IRD (improvement rate difference) is a nonparametric measure of nonoverlap for comparing two phases, typically Baseline and Treatment phases. IRD equals the difference between the two “improvement rates” for a Baseline and a Treatment phase. It does not include data trend. IRD is appropriate for nearly all data types and distributions, including dichotomous data. IRD was modeled after the “Risk Difference” concept used in group medical research. It is a novel method applied to single case data, first described by Parker, Vannest & Brown, 2009. Strengths of IRD are its simplicity and its reflection of visual nonoverlap. This webpage calculates “Robust IRD”. [Parker, R. I., Vannest, K. J. & Brown, L. (2009). The Improvement Rate Difference for Single Case Research. Exceptional Children. 75:2, 135-150 ]
  1. Data are input in the ten windows at the page top, each headed by a label box and a selection check.
  2. Type or paste data from just one phase in each input window, and label each phase above, e.g. A1, B3, 2A1, etc.
  3. Select only two phases for a first contrast. Select by checking beside a label.
  4. Click “IRD” button. Directly below will be provided results for that contrast.
  5. Repeat steps 3 and 4, making all phase contrasts desired. All will be saved below.
  6. To combine contrasts for a single design, use the check boxes to the left of their results (left of “id”), near the middle of the page. Select as many contrast results as desired. Then click “Combine” button below. Combined IRD effect sizes are weighted averages, where weights are the inverse of their variances. The combined SD for NAP is the square root of the sum of NAP variances involved.
  7. The final “weighted average” button permits any combination of individual contrasts or combined contrasts, by first checking them above. The combination algorithms are the same as in #6 above.

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