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Epidemiology and Population Health

Measurement rigor is not a substitute for design rigor in causal inference: increased physical activity does cause (modest) weight loss

International Journal of Obesity volume 47, pages 3–4 (2023)Cite this article

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We read with interest a recent article in Science entitled “The Calorie Counter” describing the work of Professor Herman Pontzer et al. on energy balance, especially physical activity [1]. We also listened to two recent interviews with Dr. Pontzer where he appeared on NPR (Pontzer Interview on NPR) and Dr. Oz (Pontzer Interview on Dr. Oz). Dr. Pontzer’s work is highly important, interesting, and exemplary in its use of scientifically sound measures of energy metabolism, which represents a substantial advancement in the field that relies on patently inadequate measures of energy expenditure and physical activity [2].

However, we take issue with two points. The first is well-known, but often neglected. It is to make inferences about causal effects that negate the dictum that “correlation does not necessarily imply causation,” as well as its contrapositive that lack of correlation does not necessarily imply lack of causation. No amount of measurement quality, new technology, or large sample size can substitute for randomization of experimental units to different levels of the independent variable (i.e., the postulated causal factor) in allowing causal inferences to be made. This has been demonstrated theoretically [3, 4] and illustrated empirically [5]. This is not merely a pedantic point, but an increasing concern in science where trust in “communication of science” is at stake [6, 7]. It is also of concern in some fields of human investigation where observational studies prevail and where causal inferences are often defended on the basis of large sample size.

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Authors and Affiliations

  1. Indiana University School of Public Health-Bloomington, 1025 E 7th Street, PH 111, Bloomington, IN, 47405, USA

    David B. Allison

  2. Baylor College of Medicine, Houston, TX, USA

    Dennis M. Bier

  3. University of Alabama at Birmingham Department of Medicine, Birmingham, AL, USA

    Julie L. Locher

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  1. David B. Allison
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  2. Dennis M. Bier
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  3. Julie L. Locher
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Contributions

DBA conceived of the work that led to the submission, and all authors played an important role in interpreting the results. All authors drafted or revised the paper, approved of the final version, and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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Correspondence to David B. Allison.

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Competing interests

In the last 36 months, Dr. DBA has received personal payments or promises for same from: Alkermes, Inc.; Amin Talati Wasserman for KSF Acquisition Corp (Glanbia); Big Sky Health; Kaleido Biosciences; Law Offices of Ronald Marron; Medpace/Gelesis; NAS/NASEM; and Novo Nordisk Fonden. Donations to a foundation have been made on his behalf by the Northarvest Bean Growers Association. Dr DBA’s institution, Indiana University, and the Indiana University Foundation have received funds or donations to support his research or educational activities from: Alliance for Potato Research and Education; American Egg Board; Arnold Ventures; Eli Lilly and Company; Haas Avocado Board; Mars, Inc.; National Cattlemen’s Beef Association; USDA; NAS/NASEM; Soleno Therapeutics; WW (formerly Weight Watchers); and numerous other for-profit and non-profit organizations to support the work of the School of Public Health and the university more broadly. Neither Drs DMB or JLL have any competing financial interests, or other conflict, related to this commentary.

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Allison, D.B., Bier, D.M. & Locher, J.L. Measurement rigor is not a substitute for design rigor in causal inference: increased physical activity does cause (modest) weight loss. Int J Obes 47, 3–4 (2023). https://doi.org/10.1038/s41366-022-01234-9

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