Question

What is the difference between an efficacy study and an effectiveness study? Explain why each is important? What phase of clinical trials are these done?

Answer 1

# Introduction

Efficacy trials (explanatory trials) determine whether an intervention produces the expected result under ideal circumstances. Effectiveness trials (pragmatic trials) measure the degree of beneficial effect under “real world” clinical settings.

Efficacy, in the health care sector, is the capacity for beneficial change (or therapeutic effect) of a given intervention (for example a drug, medical device, surgical procedure or a public health intervention) under ideal or controlled conditions.

Effectiveness links to the notion of external validity, in that it refers to patients who are visited by physicians in their everyday practice.

# What is the difference between an efficacy study and an effectiveness study?

Efficacy, in the health care sector, is the capacity of a given intervention under ideal or controlled conditions. Effectiveness is the ability of an intervention to have a meaningful effect on patients in normal clinical conditions. Efficiency is doing things in the most economical way.

# Importance

When developing a new or experimental intervention, an efficacy study might be important to increase the likelihood of detecting a positive change. However, “real world” factors may make a difference in how a product is used. Perhaps an intervention might be inconvenient (due to multiple doses throughout the day) or unpalatable for the patient. Perhaps the dosing regimen is complicated and the primary care providers don’t apply the correct dosing for patients. In these cases, an effectiveness study might be a better guide to how useful the intervention will be in clinical practice.

As a final note, it can be tempting to simply read the abstract of a clinical trial to assess the results of a study. However, in many instances the crucial details of the study (e.g., how the study participants were selected, who was included or excluded, what type of clinical setting was used) are buried in the methods section of the study. Patient diet, exposure to other treatments and comorbid conditions are all common confounding factors encountered in trials evaluating supplements.

# What phase of clinical trials are these done?

Clinical trials of drugs are usually described based on their phase. The FDA typically requires Phase I, II, and III trials to be conducted to determine if the drug can be approved for use.

* A Phase I trial tests an experimental treatment on a small group of often healthy people (20 to 80) to judge its safety and side effects and to find the correct drug dosage.

* A Phase II trial uses more people (100 to 300). While the emphasis in Phase I is on safety, the emphasis in Phase II is on effectiveness. This phase aims to obtain preliminary data on whether the drug works in people who have a certain disease or condition. These trials also continue to study safety, including short-term side effects. This phase can last several years.

* A Phase III trial gathers more information about safety and effectiveness, studying different populations and different dosages, using the drug in combination with other drugs. The number of subjects usually ranges from several hundred to about 3,000 people. If the FDA agrees that the trial results are positive, it will approve the experimental drug or device* Phase IV trial for drugs or devices takes place after the FDA approves their use. A device or drug's effectiveness and safety are monitored in large, diverse populations. Sometimes, the side effects of a drug may not become clear until more people have taken it over a longer period of time.