An engineer designs an improved light bulb. The previous design had an average lifetime of 1200 hours. The new bulb has a lifetime of 1201 hours, using a sample of 2000 bulbs. Although the difference is quite small, the effect was statistically significant. The explanation is that new designs typically have more variability than standard designs new designs typically have more variability than standard designs the mean of 1200 is large the mean of 1200 is large the new bulbs last longer than the old bulbs the new bulbs last longer than the old bulbs the sample size is very large the sample size is very large all of the above