In Exercises 21–28, determine whether the study is an experiment or an observational study, and then identify a major problem with the study.

Atkins Weight Loss Program An independent researcher tested the effectiveness of the Atkins weight loss program by randomly selecting 1000 subjects using that program. Each of the subjects was called to report their weight before the diet and after the diet.

A study is conducted to test the effectiveness of a weight loss program using a sample of 1000 subjects. The subjects are required to inform their weights before and after diet.

A collection of observations of the subjects of a sample without altering any of them is termed anobservational study. The researcher simply observes the behavior and states it explicitly.

The testing of an effect on a group of subjects by altering one or more aspects of each of the subjects is termed anexperimental study. The researcher manipulates the surroundings in which the study is performed to practically analyse the results that are free from biases.

The study deals with assessing the effectiveness of the weight loss program without inducing any modifications in the subjects. However, it does not mention anything about altering the subjects (increase/decrease in weight). Thus, it is anobservational study.

In a survey study,voluntary responses of the subjects can result in theinaccuracy of the analysis reports that are based on these responses.

Since the subjects have reported their pre-diet and post-diet weights voluntarily without any verification of the values by the researcher using a scale, the results will be inaccurate.