Two independent samples ttest

When you want to compare the mean score on a continuous variable for two different
groups of participants (two populations, one variable)

Will tell you whether there is a statistically significant difference in the mean scores of
two groups (whether males and females differ significantly in terms of their perception
levels)
Step one: formulate the null and alternative hypothesis
Same mean preference (null) or different mean preference (alternative)
Step two: test equality of variance
Equal variances H
0
Variance are different (H
1
)
Firstly, you must test the equality of variances.
Looking at equal variances assumed look at sig (can either reject or accept H
0
of equal
variances)
Then look at sig (2tailed) (either reject or accept H
0
of equal means)
Oneway analysis of variance (ANOVA)

Used when you have one independent variable with three or more levels (groups) and
one dependent continuous variable

Will determine if there is a significant difference in the mean scores on the dependent
variable across the three groups
Dependent variable (DV) = metric (Y)
Independent variable (IV) = categorical (X)
All have the same effect/influence (null hypothesis)
All have different effect/influence (alternative hypothesis)
Look at sig and determine whether to reject or accept null hypothesis
To determine the strength, divide between groups by the total
Correlation and regression
Correlation

Relationship between two metric variables

Used to describe the strength of direction of the linear relationship between two
variables
There is no linear association (null)
There is a linear association (alternative)

Look at sig (2tailed) to determine if there is an association or not

Then look at pearson correlation to determine the strength of the association (01)
Linear (multiple) regression
A statistical procedure for analysing associative relationships between a metricdependent
variable and one or more metric independent variables.
It tells you how much of the variance in your dependent variable can be explained by your
independent variables. It also gives you an indication of the relative contribution of each
independent variable.
Form a null and alternative hypothesis for each variable

First check if the model is valid (F test) by looking at regression sig

Explain the coefficients by looking at the sig of each and determine whether to accept or
reject the null hypothesis for each one

Look at the fit of the model by R square (01)
Causal Research
What is causal research (causal inference)?
Most interesting questions in marketing (and life) are causal questions

Does higher price lead to more profit?

Did the new ad campaign work (i.e., increase revenue/profit/brand equity)?

Is smoking bad for your health?
But there are a lot of confusion around causality

People use the term loosely (and confuse causality with empirical association)

Establishing causality is complicated
Two variables

X and Y
Definition of causal inference

Whether a change in one marketing variable (X) produces a change in another variable
(Y)
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 Fall '17
 Erica Brady