Time-reversed Analysis

David A. Kenny

December 24, 2013

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The Basic Idea• Redo the analysis but flip or reverse the flow

of time.• So for a two-wave study, have Time 1

become Time 2 and Time 2 become Time 1.• See Campbell & Kenny, A Primer on

Regression Artifacts (1999), pp. 158-163 for details.

So instead of T1 T2 …

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You have T2 T1 …

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Why?• If you get essentially the same pattern of

results in the time-reversed analysis, as in the original analysis, that calls into question the original analysis.

• For the above figures, if we find that the path from X to Y is bigger than the path from Y to X in both the regular and the time-reversed analysis, we should be suspicious of analyses.

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A Nonsensical Analysis?• A time-reversed makes no sense.• The idea is that if the results from a

nonsense analysis make as much as the regular analysis, then maybe the regular analysis does not make sense.

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When to Consider a Time-Reversed Analysis?

• Some analysis techniques yield the opposite results when a time reversed analysis is performed.

• For example if X is regressed on Y2 – Y1 (i.e., change) to yield b, then when X is regressed on time reversed change or Y1 – Y2, the result is –b.

• A time-reversed analysis is more useful when an earlier time is used to predict a later time.

• If regression toward the mean is a plausible explanation of a result, then a time-reversed analysis might be beneficial.

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An IllustrationKee, K. S., Qreen, M. F., Mintz, J., &

Brekke, J. S. (2003). Is emotion processing a predictor of functional outcome in schizophrenia? Schizophrenia Bulletin, 29, 487-497.

(If you have an illustration, please let me know.)