Terms  Definitions 

Measures of central tendency 
mean, median, mode

Mean 
average of all scores

Median 
midpoint of all scores

Mode 
most frequently occurring score

mean is appropriate for what data types? 
interval, ratio

median is appropriate for what data types? 
ordinal data

mode is appropriate for what data types? 
nominal

Measures of variability 
range, standard deviation, normal distribution, percentiles & quartiles

Range 
difference between highest and lowest score

Standard Deviation 
variability of scores from the mean. most frequently used

How to calculate SD 
subtract each score from mean, square each difference, add up all squares, divide by number of scores

Normal distribution 
symmetrical bell shaped curve indiecating distribution of scores. Mean/median/mode all similar.

Inferential statistics 
allow determination of how likely results can be generalized to a population

Standard error of measurement 
an estimate of expected errors in a score, measure of response stability or reliability

Tests of significance 
estimation of true differences not due to chance, rejection of null hypothesis

Alpha level 
probability level  reselected level of statistical significance. Most commonly .05 or .01 (.05= only 5x out of 100 is the difference due to chance)

Degrees of freedom 
based on # of subjects and groups, allows determination of level of significance

Standard error 
result of sampling error, expected chance variation among the means

Type 1 error 
Null hypothesis rejected when it is true.

Type 2 error 
Null hypothesis is not rejected when it is false. means concluded to be due to chance when truly different

How to decrease type 1/2 errors 
increase sample size, random selection, valid measures

Parametric statistics 
Interval or Ratio data

Assumptions for parametric statistics 
normal distribution (usu large representative samples this is met), random sampling performed, variance in groups is equal

Ttest 
parametric test of significance used to compare 2 independent groups created by random assignment and ID difference at a selected probability level

Ttest for independent samples 
compares 2 independent groups

Ttest for paired samples 
compares 2 matched samples (does therapy incr fxn in siblings with autism)

Onetailed Ttest 
based on directional hypothesis. Evaluates differences in data on only one end of distribution (neg or pos)

Twotailed Ttest 
based on a nondirectional hypothesis. Evaluates differences in data on both ends of a distribution. Tests of signif are almost always twotailed

Inappropriate use of Ttest 
use to compare more than 2 means within a single sample.

ANOVA 
parametric test used to compare 3 or more independent tx groups at a selected probability level.

Simple (oneway) ANOVA 
compares multiple groups on a single IND variable. Ex: Balance Master score for 3 different age groups

Factorial ANOVA 
compares multiple groups on two or more IND variables. Ex: 3 levels of ankle injury compared for balance and sensory

ANCOVA 
Parametric test used to compare 2 or more treatment groups or conditions while also controlling for the effectss of intervening variables.

Nonparametric statistics 
ORDINAL or NOMINAL data, testing not based on population parameters

When to use nonparametric 
parametric assumptions cannot be met. used with small sample, ordinal or nominal level data. Less powerful than parametric

Chi square test 
nonparametric test of significance. Used to compare data in the form of frequency counts in 2 or more mutually exclusive categories (rate treatment preferences)

Correlational statistics 
used to determine the relative strength of a relationship between 2 variables

Pearson productmoment coefficient (r) 
used to correlate CONTINUOUS data wi

Linear Regression 
used to establish relationship between two variables as a basis of prediction

Spearman's Rank 
NONPARAMETRIC test to correlate ORDINAL data.

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