Calculations and Formulas

Mean

The average: adding the scores and dividing by the number of scores.

Median

The middle score in a distribution: half the scores are above and half are below

Mode

the value that occurs most frequently in a given data set

Normal distribution

A bell-shaped curve, describing the spread of a characteristic throughout a population

Range

The difference between the highest and lowest scores in a distribution

Standard deviation

A measure of variability that describes an average distance of every score from the mean

Standard error of the mean

the standard deviation of the sampling distribution of the mean

Error bars

Reflect standard deviations of confidence intervals

Positive control group

Effect should be seen in this group because they are expected

Negative control group

Control group that is not exposed to the experimental treatment or to any other treatment that is expected to have an effect.

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Simply: the experiment that are treated the same as all the others but are not expected to change from any variable in the experiment.

Null hypothesis (H0)

the statistical hypothesis tested by the statistical procedure; usually a hypothesis of no difference or no relationship

Alternative hypothesis (Ha)

Hypothesis in which there are effects or a relationship