2017/06/17

Basic Statistical Concepts

nominal - male vs. female/  frequencies , percentages (non-parametric)
ordinal - e.g. Likert scale / first,second, third (non-parametric)
interval - discrete, parametric , continuous (eg temperature)
Ratio level - usually interval data, zero point reflects absence of characteristic

Discrete - adult/ non adult 
Continuous - angry to super angry 

Test Statistic = Systematic Variance / Unsystematic variance
We are comparing the amount of variance created by an experimental effect against the amount of variance due to random factors (such as differences in motivation, or intelligence)

t-value 
what is the probability that our samples are from the same population . You basically compare the means of two or more samples
it is a measure of unsystematic variance or variance not caused by the experiment

r-value (Effect Size)
is simply an objective and standardized measure of the magnitude of the observed effect. 
Pearson Correlation Coefficient
r = .1 (weak effect) 1% of variance between variables is explained
r = .3 (medium effect). 9% of variance between variables is explained
r = .5 (strong effect) 25% of variance is explained

p-value 
Significance - Chance of Error (being wrong), in other words the chance of a finding being due ot error
The chance of the null hypothesis to be rejected where it is actually true.
in Business this is accepted

p < .05

z-value 
are standard scores. it states the position of a raw score in relation to the mean of the distribution, using the standard deviation as the unit of measurement
z = raw score - mean / standard deviation

Standard Error 
the  standard deviation (or variability) of sample means. The higher the SE, the more the sample means differ from each other
The lower it is the more it accurately reflects the entire population


Mean: Sum / n
Median: right in the middle of samples
Mode: the most occuring

Standard Deviation 
Average distance of the values from the mean

Variance Extracted 
Summary measure of convergence among a set of items representing a latent construct.
It is the average % of variation explained among items



Type 1 Error (False Positive) 
Accepting effects that are in reality untrue

Type 2 Error (False Negative) 
Rejecting effc├ęcts that are in reality true


Construct Validity (relationship betweeb measurement instrument and the construct)
Discriminant, Convergent, nomological validity

Discriminant Validity
Eg how good do the items of the construct of innovation differentiate from frome the construct of strategic validity

Convergent Validity
How good are the items for the innovation construct converging ?
If they do not converge the are likely not measuring the same phenomenon
- Cronbach Alpha, cut-off value > .70
- Composite reliability, cut-off value > .60
- AVE Average variance extracted, cut-off value AVE > .50
(AVE = average squared factor loading)

Indicator reliability / validity
- significant factor loadings of items >.70, t-values > 1.645

Multicollinearity
phenomenon in which two or more predictor variables in a multiple regression model are highly correlated, meaning that one can be linearly predicted from the others with a substantial degree of accuracy

Solution:
Variance inflation factors (VIF) measure how much the variance of the estimated regression coefficients are inflated as compared to when the predictor variables are not linearly related.
Use to describe how much multicollinearity (correlation between predictors) exists in a regression analysis. Multicollinearity is problematic because it can increase the variance of the regression coefficients, making them unstable and difficult to interpret.


Parametric Tests 
Kolmogorov Smirnov Test 
if p > .05 distribution is probably normal 

Levene Test 
tests hypothesis that variances of two samples are equal
if p > .05 variances are more or less equal