The is the entire group being studied. A is a group that is selected from the population. You can generate a simple sample using excel or your calculator. In a distribution the left is roughly a mirror image of the right. Other data distributions are left skewed or right also known as negatively or skewed. Data that can be paired is data, for example, height versus armspan. A is used to see if there is a correlation between them. If r, the correlation , is close to 1 there is a strong positive correlation. If r is close to -1, there is a strong correlation. If r = 0 then there is correlation. The measures of central tendency are the mode, the and the median. To find the , rank the data first and then choose the middle value. The measures of spread are the standard , the interquartile range and the range. The range is the difference between the highest and lowest values. The range is the range of the middle 50%. When deciding which average to use, if there are outliers, choose the not the mean and if the data is not numerical choose the . In any normal distribution, 68% of the lie within one standard deviation of the mean: this is the rule.