Question

For each of the following cases [(a) (b)], (I) state whether the study should be observational or experimental. (II) state whether the study should be run blind, doubleblind, or neither. If the study should be run blind or double-blind, who should be blinded? (a) An investigation of whether taking aspirin reduces one's chance of having a heart attack. (b) An investigation of whether babies born into poor families (family income below \(\$ 25,000\) ) are more likely to weigh less than 5.5 pounds at birth than babies born into wealthy families (family income above \(\$ 65,000\) ).

Short answer

Case (a) should be an experimental, double-blind study with both participants and researchers blinded. Case (b) should be an observational study, with neither blind nor double-blind methods needed.

Step-by-step solution

Determine Study Type for Case (a)

In case (a), the question is about the effect of taking a specific medication (aspirin) on a health outcome (chance of having a heart attack). Since the goal is to evaluate the effectiveness of an intervention (aspirin), this should be an experimental study. In an experimental study, researchers actively intervene by controlling who receives the treatment and who does not.

Determine Blindness for Study (a)

For the study in case (a), it should be run as a double-blind study to prevent bias. Both the participants and the researchers who interact with them should be blinded to whether the participants are receiving the actual treatment (aspirin) or a placebo. This is because the knowledge of who is receiving the treatment can influence both the participants' and researchers' behaviors and assessments.

Determine Study Type for Case (b)

In case (b), the investigation is about the relationship between family income and newborns' birth weight. This study should be observational because it is not ethical or practical to manipulate people's family income. In an observational study, researchers simply observe and record the outcomes without intervening or imposing treatments.

Determine Blindness for Study (b)

For case (b), neither a blind nor double-blind study is necessary because the data on family income and babies' birth weights can be collected without any need for concealment. The investigator or the data collector does not require blinding as these are not subjective measurements that can be influenced by participants' or researchers' expectations.

Key concepts

Observational Study

When students encounter the term 'observational study,' it describes a research method in which outcomes are observed without manipulating any variable. Unlike an experimental study, researchers do not change the environment or apply specific treatments to the participants. An observational study is ideal for situations where it is not ethical or practical to conduct an experiment. For example, investigating the relationship between family income and babies' birth weights, as in case (b), is apt for an observational study since altering people's income for research is neither ethical nor feasible.

Key aspects of observational studies include:

• Real-world data collection without intervention.
• Utilizing existing variations in the population, like economic status or lifestyle habits.
• Ability to study outcomes in large groups over time.
• Useful for generating hypotheses that can be later tested with experimental studies.

However, there's a limitation to consider: observational studies cannot conclusively show causation due to potential confounding variables.

Experimental Study

An 'experimental study' takes a step further into scientific inquiry by carefully manipulating one or more variables to observe their effect on other variables. This design allows researchers to establish causality rather than mere correlations. For instance, in case (a), where the effect of aspirin on reducing heart attack risk is investigated, an experimental study is appropriate. Researchers control who receives aspirin (treatment group) and who receives a placebo (control group), providing strong evidence for aspirin's effectiveness.

The strengths of experimental studies are:

• Ability to isolate and test the effects of a specific variable.
• High control over the research environment.
• Easier to replicate for verifying results.

This control, however, comes with a caveat. Experimental studies often take place under conditions that may not perfectly mirror real-world settings, which can limit the generalizability of the findings.

Double-Blind Study

The concept of a 'double-blind study' is pivotal in eliminating bias and ensuring the reliability of an experiment's results. In a double-blind study, neither the participants nor the researchers know who is receiving the actual treatment versus a placebo. This kind of study is the gold standard, particularly in clinical trials, such as the aspirin efficacy study in case (a). By blinding both parties, the study maintains objectivity and reduces the placebo effect and observer bias.

Key features of a double-blind study include:

• Blinding of participants to prevent the placebo effect.
• Blinding of researchers to avoid unconscious bias in data collection or interpretation.
• Often used in conjunction with randomized trials to improve validity.

Despite its strengths, double-blind studies are complex to administer and may not always be possible due to the nature of some treatments or interventions.