# Normality

## Continuous variables must possess normality in order to use parametric statistics

The statistical assumption of normality is

**central**to conducting inferential statistics using continuous variables and outcomes. A**normal distribution resembles the "bell curve"**where the mean, median, and mode of a distribution are all the same. In a normal distribution, 68% of all observations will fall within one standard deviation above and below the mean, 95% will occur within two standard deviations above and below the mean, and 99.5% of all observations will exist within three standard deviations above and below the mean. The assumption of normality is tested for when employing parametric statistics with continuous variables and outcomes.### Normality and applied statistics

Whenever using a

If a continuous variable's distribution yields skewness and kurtosis statistics

In certain instances, an

**continuous variable**, researchers must check the normality of the continuous variable's distribution using**skewness and kurtosis statistics**. If a continuous variable has a skewness or kurtosis statistic**above an absolute value of 2.0**, then the variable is assumed to have a non-normal distribution. Check for**outliers**, or observations that are more than 3.29 standard deviations away from the mean, and make a decision to 1)**delete**the observation in a listwise fashion, 2) conduct a**logarithmic transformation**to "normalize" the distribution, or 3) employ**non-parametric statistics**to yield inferences.If a continuous variable's distribution yields skewness and kurtosis statistics

**below an absolute value of 2.0**, then the assumption of normality has been met. More powerful**parametric statistics**can be used on continuous variables that meet the assumption of normality.In certain instances, an

**ordinal variable**can be upgraded to an**interval scale of measurement**if the assumption of normality is met for the ordinal distribution. This is especially true if the ordinal variable is a**Likert-type score yielded from an empirically-validated instrument**. More statistical power is achieved for these types of ordinal variables if the assumption of normality can be met and parametric statistics are used.## Hire A Statistician - Statistical Consulting for Students

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