Platelet-Rich Plasma Does a platelet-rich plasma (PRP) injection into the scalp promote hair growth? Researchers identified 30 female patients with female pattern hair loss. The patients ranged in age from 20 to 45 years. For each patient, two areas with hair loss were identified. A coin toss was used to decide which area received the PRP injection and which received a saline injection. Injections were given to each patient at one-week intervals. After 6 months the change in the patients’ hair density (number of hairs per square centimeter) and hair diameter (millimeters) was measured. The mean difference in hair density (PCP minus saline) was 59.47 hairs/cm2 and the mean difference in hair thickness was 0.08 mm.


What type of experimental design is this?

Verified step by step guidance

1. Step 1: Identify the subjects and treatments involved. Here, 30 female patients with hair loss are studied, and each patient receives two treatments: a platelet-rich plasma (PRP) injection and a saline injection.
2. Step 2: Note that for each patient, two different areas of hair loss are selected, and one area receives the PRP injection while the other receives the saline injection. The assignment of which area gets which treatment is randomized by a coin toss.
3. Step 3: Recognize that the same patient experiences both treatments, meaning the comparison is made within the same individual rather than between different individuals.
4. Step 4: Understand that this design controls for individual differences because each patient serves as their own control, reducing variability caused by differences between patients.
5. Step 5: Conclude that this is a "within-subjects" or "repeated measures" experimental design, specifically a randomized paired design where each subject receives both treatments in different areas.

Key Concepts

Within-Subjects Design

A within-subjects design involves the same participants receiving multiple treatments or conditions. In this study, each patient received both the PRP injection and the saline injection on different scalp areas, allowing direct comparison within the same individual. This design helps control for individual differences that could affect the outcome.

Randomization

Randomization is the process of assigning treatments to subjects or conditions by chance to reduce bias. Here, a coin toss was used to randomly decide which scalp area received the PRP or saline injection, ensuring that treatment assignment was unbiased and that confounding variables were minimized.

Controlled Experiment

A controlled experiment includes a treatment group and a control group to compare effects. In this case, the PRP injection is the treatment, and the saline injection serves as the control, allowing researchers to isolate the effect of PRP on hair growth by comparing it against a placebo.