### median

the middle value of a group of values, found by arranging all the observations from lowest value to highest value and picking the middle one

### variance

a measure of the spread of values within a group; calculated by dividing the sum of each values variation (the difference between the value and the mean) squared by the count (total number of values) minus one

### standard deviation

the average difference of each value in a group from the mean value; calculated by taking the square root of the variance

### confidence interval

the level of certainty that the true score falls within a specific range. The smaller the range the less the certainty.

### interquartile range

the difference between the scores (or estimated scores) at the 75th percentile and the 25th percentile. Used more than the range because it eliminates extreme scores.

### skewed distribution

not normal, or not bell curved, Any distribution of values which is not normal, that is not symmetrical along the x-axis

### normal distribution

symmetrical distribution of values (mean=median) expected when a sample is taken from a large population; forms a bell-shaped curve called the normal curve

### standard error of the mean

a measure of precision, the index that tells us how much a particular mean is likely to vary from one sample to another when all samples are drawn from the same population; the standard deviation of the sampling distribution of the mean

### p value

the probability that the differences between two groups of values are due to chance; i.e. the probability that a null hypothesis has been mistakenly rejected, the probability that you have a false positive

### p<.05

generally accepted characteristic of significant results, meaning the probability that the null hypothesis was mistakenly rejected is less than 5%, i.e. the probability that the null hypothesis is false is 95%

### p >.05

the probability that randomly generated results would resemble the observed results is more than 5%, rendering the results not significant

### the t test

assesses whether the means of two groups (eg. control group and experimental group) are statistically different from each other, assumes that each group is sampled from different populations and that the distributions of the variable of interest are normal;

### linear regression

defines a line of best fit for correlational data that can be used as a prediction equation

### correlation

a measure of the extent to which two factors vary together (covary); a reciprocal relation between two or more things; CORRELATION DOES NOT ENTAIL CAUSATION, but it does suggest causation