Bias, withdrawal Error due to characteristics of those participants who choose to withdraw from a study or become lost to follow up. Causation Statistical methods alone cannot establish a causal relationship between factors. Central tendency, mode The most frequently occurring observation. Chance Random variation, i.e., the happening of events without an apparent cause. Data, interval Data classified into equal intervals without an absolute zero point, e.g., I.Q. of 120 is 60 points higher than an IQ of 60, but this does not necessarily indicate twice as much intelligence.
Temperature is another example.
Data, ratio Data classified into an interval scale with an absolute zero point so that ratios between values are meaningful, e.g., weight, height, income. Distribution, bimodal A distribution having two peaks of high frequency of observations separated by a region of low frequency observations. A symmetrical distribution which has a shape defined by its mean and standard deviation. Often called the bell-shaped curve. A line graph of observation frequencies forming an illustration of a distribution.