Education and cognitive activity have been suggested to protect against cognitive decline in old age. However, little is known about the long-term effects of extremely high levels of education and intellectual activity across the lifespan. The present study investigated the extent to which these two variables may moderate the age-related differences in cognitive performance in old adults. There...

OBJECTIVE In ex vivo hip fracture studies femoral pairs are split to create two comparable test groups. When more than two groups are required, or if paired femurs cannot be obtained, group allocation according to bone mineral density (BMD) is sometimes performed. In this statistical experiment we explore how this affects experimental results and sample size considerations. METHODS In a hip f...

In statistic tests, the probability distribution of the statistics is important. When samples are drawn from population N (µ, σ(2)) with a sample size of n, the distribution of the sample mean X̄ should be a normal distribution N (µ, σ(2)/n). Under the null hypothesis µ = µ0, the distribution of statistics [Formula: see text] should be standardized as a normal distribution. When the variance of ...

The one-sample paired t-test may be used to test whether the mean difference of two populations is greater than, less than, or not equal to a specific value. Because the t distribution is used to calculate critical values for the test, this test is often called the paired t-test. If the standard deviation of the differences is known, the normal distribution is used instead of the t distribution...