Final answer:
Faith's experiment has a selection bias due to the non-representative sample of her family members, affecting the validity of the results. A more valid approach would be a randomized controlled trial with a diverse sample and control groups.
Step-by-step explanation:
The bias in Faith's experiment to test the effects of a weight-loss supplement is selection bias. Since she asks several of her family members to participate, the sample may not be representative of the general population. This bias could affect the validity of the results, as family members may share similar lifestyles, genetics, and behaviors that could influence the weight loss outcomes independent of the supplement's effectiveness.
To address this bias and conduct a more scientifically sound experiment, a randomized controlled trial with a representative sample is necessary. Including control groups and possibly a placebo group would also improve the study design and provide more reliable data on the supplement's effects on weight loss.