A health education specialist evaluated the impact of a no-smoking policy and found significant lower rates of smoking in the intervention group. Which probability level indicates the results are least likely due to chance?

A probability level of P=.001 indicates that the results are very unlikely to have occurred due to chance. In statistical terms, a P-value represents the probability of obtaining results as extreme as the observed results, assuming that the null hypothesis is true (which typically postulates no effect or no difference). A P-value of .001 signifies that there is only a 0.1% chance that the observed differences in smoking rates are due to random variability rather than a genuine effect of the no-smoking policy.

This very low probability suggests strong evidence against the null hypothesis, meaning the health education specialist can be more confident that the intervention had a real and significant impact on reducing smoking rates. In research, a smaller P-value indicates stronger evidence for the existence of an effect, making P=.001 a more reliable indicator compared to higher P-values, such as .01 or .10, which suggest a greater likelihood that the findings could be due to chance.

Choosing a P-value of .001 reflects a higher level of statistical significance, leading to more robust conclusions regarding the effectiveness of the intervention.