Approximately what percentage of scores fall within one standard deviation of the mean in a normal distribution?

Approximately what percentage of scores fall within one standard deviation of the mean in a normal distribution? (a) 34%

(b) 95%

(c) 99%

(d) 68%

✅ Correct option: (d) 68%

Explanation:

In a normal distribution, data follow a symmetrical bell-shaped curve. According to the Empirical Rule (68–95–99.7 rule), approximately 68% of the scores fall within one standard deviation above and below the mean. This rule helps researchers quickly understand how data are distributed without complex calculations. About 95% of the data fall within two standard deviations, and nearly 99.7% fall within three standard deviations. Understanding this concept is essential in educational testing, psychology, and research interpretation because it allows estimation of score distribution and probability. Therefore, the correct answer is 68%.

10 Related PPSC Facts:

Normal distribution is symmetrical. Mean, median, and mode are equal. 68% lies within ±1 SD. 95% lies within ±2 SD. 99.7% lies within ±3 SD. Empirical rule applies only to normal curves. Standard deviation measures spread. Bell curve is common in test scores. Z-scores rely on normal distribution. Larger SD means more variability.