Impact of the Hawthorne Effect in a Longitudinal Clinical Study: The Case of Anesthesia

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Abstract

Clinical research can be influenced by many factors that are capable of invalidating results, and one of these factors is known as the Hawthorne effect: the mere awareness of being under observation can alter the way in which a person behaves. In experimental research this effect can be the undesired effect of the experiments themselves, and the stronger its presence, the greater it can influence the results. In anesthesia practice, owing to the particular emotional condition of a patient facing a surgical operation, the Hawthorne effect could be especially strong. The aim of our study was to show the impact that the knowledge of being included in a study has (Hawthorne effect), by comparing the postoperative changes in psychological well-being in two groups of patients undergoing knee arthroscopy and receiving different information about the study from the anesthetist during the preoperative interview. Other signs and symptoms such as postoperative knee pain, nausea, vomiting (the most feared occurrences), headache, return of spontaneous diuresis, analgesic request, anesthesia complications, as well as the intensity of anxiety were also assessed as secondary endpoints.

Our results show that subjects who were aware that they were part of a study scored significantly better on postoperative measures of psychological well-being and postoperative knee pain, compared to subjects who were unaware. The size of the effect, as measured by the odds ratio, remains unchanged when controlling for potential confounding factors. The study has enabled us to demonstrate the presence of the Hawthorne effect in clinical research. Therefore, the Hawthorne effect should be acknowledged and accounted for in the design of a study and in the interpretation of results. Control Clin Trials 2000;21:103–114

Introduction

Clinical research can be influenced by many factors that are capable of invalidating results. One of these factors is known as the Hawthorne effect, a name derived from experimental studies carried out from 1924 through 1932 in the Hawthorne Works Plant of the Western Electric Company in Chicago [1]. These studies were conducted with a view to improving the productivity of workers by changing their environmental conditions. For example, more light was accompanied by increased productivity but less light also increased productivity. Thus the company's efforts produced conflicting results, because any change in working conditions, however insignificant, led to greater productivity. The subjects increased their productivity in response to the increased attention and to the subtle pressure of being observed. It was recognized that what later came to be called the Hawthorne effect was responsible for this. Man has a natural propensity to be influenced by being observed, and therefore the mere awareness of being under observation can alter the way in which a person behaves.

In experimental research this can be the undesired effect of the experiments themselves, and the stronger its presence, the greater it can influence the results. Therefore risk exists that what is simply the consequence of a patient knowing that he is observed can be mistaken for the outcome of a specific intervention. This should be borne in mind both when preparing the study design and when analyzing the results 2, 3, 4, 5.

In the clinical setting an emotional involvement related to the patient-doctor relationship is inevitable, and could induce the Hawthorne effect. Actually, the latter could be especially strong in the practice of anesthesia, owing to the particular emotional condition of a patient facing a surgical operation, and it might therefore influence the results of clinical research in anesthesiology. More than 30 years ago it was discovered that the meeting between patient and anesthetist and the type of information given to the patient can have a positive or negative influence on his state of psychological well-being and on postoperative morbidity 6, 7, 8, 9, 10, 11.

The aim of our study was to show the impact that the knowledge of being included in a study has on a trial (Hawthorne effect), by comparing the postoperative changes in psychological well-being in two groups of patients undergoing knee arthroscopy and receiving different information about the study from the anesthetist at the preoperative interview. Other signs and symptoms such as postoperative knee pain, nausea, vomiting (the most feared occurrences), headache, return of spontaneous diuresis, analgesic request, anesthesia complications, as well as the intensity of anxiety were also assessed as secondary endpoints.

Section snippets

Study Design

The study was designed as a randomized controlled clinical trial. Two groups of patients were compared: an “additional information group” (exposed group), patients who were informed that they were taking part in a trial; and a “routine information group” (control group), patients who were not. Patients were assigned to one of the two groups according to a simple randomization scheme. It was calculated that a sample size of 58 patients per group would guarantee a power for the study of 80% with

Results

A total of 116 patients were enrolled in the study: 56 patients were included in the control group and 60 in the exposed group. Baseline characteristics of the patients are shown in Table 1. Mean GHQ score was 2.3 (SD 3.1) in the control group and 2.7 (SD 2.6) in the exposed group. Fourteen patients in both groups (25.0 and 23.3%, respectively) had a score ⩾ 6 at the baseline assessment.

Results

Our study was aimed at uncovering the Hawthorne effect, namely the tendency of people to change their behavior because of their being observed, in a clinical longitudinal study. Most articles published in the literature were designed to acknowledge the Hawthorne effect in health care research (and sometimes suggest solutions to it), with particular concern for the behavior of physicians or other health care professionals 3, 4, 5, 17, 18. As far as we are aware, a single study was published in

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