Statistic definitions Flashcards
Cronbach α (Alpha)
Cronbach’s alpha is a measure of internal consistency, that is, how closely related a set of items are as a group. It is considered to be a measure of scale reliability.
A Cronbach score can be used to assess scale
reliability- with α > .70 indicative of satisfactory
reliability.
Sometimes to improve the Cronbach α, items from
a subscale are removed.
Null hypothesis: H0
In scientific research, the null hypothesis is the claim that no relationship exists between two sets of data or variables being analysed. The null hypothesis is that any experimentally observed difference is due to chance alone, and an underlying causative relationship does not exist, hence the term “null”.
Hypothesis: H1
A hypothesis is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous observations that cannot satisfactorily be explained with the available scientific theories.
Z-score
Z-score is a statistical measurement that describes a value’s relationship to the mean of a group of values. Z-score is measured in terms of standard deviations from the mean. If a Z-score is 0, it indicates that the data point’s score is identical to the mean score.
Cohens d
Cohens d is a standardized effect size for measuring the difference between two group means. Frequently, you’ll use it when you’re comparing a treatment to a control group. It can be a suitable effect size to include with t-test and ANOVA results. The field of psychology frequently uses Cohens d
Effect sizes
- 0.2 (small)
- 0.5 (medium)
- 0.8 (large)
Confidence Interval
A Confidence Interval is a range of values we are fairly sure our true value lies in. A confidence interval is the mean of your estimate plus and minus the variation in that estimate. This is the range of values you expect your estimate to fall between if you redo your test, within a certain level of confidence. Confidence, in statistics, is another way to describe probability. overall your confidence interval is the range you expect to find the r value to be 95% out of 100 samples
Bivariate
involving or depending on two variates.
Pearson correlation coefficient ( r )
What is r? Put simply, it is Pearson’s correlation coefficient (r). Or in other words: R is a correlation coefficient that measures the strength of the relationship between two variables, as well as the direction on a scatterplot. The value of r is always between a negative one and a positive one (-1 and a +1)
.50 high correlation/large effect
.30 moderate correlation/moderate effect
.10 low correlation/low effect
it can also be used to quantify the difference in means between two groups.
Correlation Coefficients
- Bounded between -1 and 1.
A correlation coefficient is a numerical measure of some type of correlation, meaning a statistical relationship between two variables. The variables may be two columns of a given data set of observations, often called a sample, or two components of a multivariate random variable with a known distribution. There are multiple Correlation Coefficients which include Covariance, Pearson’s Spearman’s, and Polychoric Correlation Coefficient. - It’s worth bearing in mind that r is not measured on a linear scale, so an effect with r = 0.6 isn’t twice as big as one with r = 0.3
Heteroscedasticity
Heteroskedasticity (or heteroscedasticity) happens when the standard deviations of a predicted variable, monitored over different values of an independent variable or as related to prior time periods, are non-constant.
Normal distribution
a function that represents the distribution of many variables as a symmetrical bell-shaped graph
Regression to the mean:
In statistics, regression toward the mean (also called reversion to the mean, and reversion to mediocrity) is a concept that refers to the fact that if one sample of a random variable is extreme, the next sampling of the same random variable is likely to be closer to its mean.
MCAR – Missing completely at random
We can test if the data is missing completely at random with a statistical test. It is called Little’s missing completely at random (MCAR) test- if the p value from the test is <.05, the data are not MCAR and listwise deletion of these cases may lead to biased/inaccurate conclusions. Imputation is justified when Little’s MCAR is < .05
Categorical variable
In statistics, a categorical variable (also called qualitative variable) is a variable that can take on one of a limited, and usually fixed, number of possible values, assigning each individual or other unit of observation to a particular group or nominal category on the basis of some qualitative property.
Examples:
- Gender
- Blood type
- Language you speak
- Country you were born etc
My words: A categorical variable has limits due to the variable having a fixed set
Variance:
The variance is the average distance of scores from the mean. It is the sum of squares divided by the number of scores. It tells us about how widely dispersed scores are around the mean.