"Putting It Together: Salk Vaccine On April 12, 1955, Dr. Jonas Salk released the results of clinical trials for his vaccine to prevent polio. In these clinical trials, 400,000 children were randomly divided in two groups. The subjects in group 1 (the experimental group) were given the vaccine, while the subjects in group 2 (the control group) were given a placebo. Of the 200,000 children in the experimental group, 33 developed polio. Of the 200,000 children in the control group, 115 developed polio.What type of experimental design is this?
e. Does it appear to be the case that the vaccine was effective?"

Verified step by step guidance

1. Step 1: Identify the type of experimental design used. Since the children were randomly divided into two groups—one receiving the vaccine (experimental group) and the other receiving a placebo (control group)—this is a randomized controlled experiment. This design helps to isolate the effect of the vaccine by controlling for other variables.
2. Step 2: Calculate the incidence (proportion) of polio in each group. For the experimental group, the incidence is given by the number of children who developed polio divided by the total number in that group: \(\frac{33}{200,000}\). For the control group, it is \(\frac{115}{200,000}\).
3. Step 3: Compare the incidence rates between the two groups. A lower incidence in the experimental group compared to the control group suggests that the vaccine may be effective in preventing polio.
4. Step 4: Consider the difference in proportions to quantify the effect of the vaccine. This can be calculated as \(\text{Incidence}_{control} - \text{Incidence}_{experimental}\). A positive difference indicates fewer cases in the vaccinated group.
5. Step 5: Reflect on the practical significance of the difference and whether the reduction in polio cases is meaningful. Since the groups were randomized and large, a substantial difference supports the conclusion that the vaccine was effective.

Key Concepts

Randomized Controlled Trial (RCT)

An RCT is an experimental design where participants are randomly assigned to either a treatment group or a control group. This randomization helps eliminate bias and ensures that differences in outcomes can be attributed to the treatment. In the Salk vaccine study, children were randomly divided into vaccinated and placebo groups, exemplifying an RCT.

Control Group and Placebo

A control group receives a placebo or no treatment, serving as a baseline to compare the effects of the experimental treatment. The placebo mimics the treatment without active ingredients, helping to isolate the vaccine's effect. Here, the control group received a placebo to measure polio incidence without vaccination.

Effectiveness of Treatment and Comparison of Outcomes

To assess treatment effectiveness, compare the incidence of the outcome between groups. A lower rate of polio in the vaccinated group compared to the control group suggests the vaccine's effectiveness. In this case, 33 cases versus 115 cases indicate the vaccine likely reduced polio risk.