Causal interference - Bivariate tests

8 important questions on Causal interference - Bivariate tests

What is an bivariate analysis?

It involves the analysis of two variables (often denoted as X, Y), for the purpose of determining the empirical relationship between them.
  • It's a very simple quantitative analysis

What can the bivariate analyse help with?

  • For testing simple hypotheses of association.
  • determine to what extent it becomes easier to know and predict a value for one variable (possibly a dependent variable) if we know the value of the other variable (possibly the independent variable).

When can we use a T-test?

The t-test can be used, for example, to determine if the means of two sets of data are significantly different from each other.
  • Strictly speaking,  it can only be used if the variances of the two populations are assumed to be equal. 
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How to perform the t-test? (three steps)

  1. Calculalte the t-value
  2. Look at the degrees of freedom
  3. Determine if the H0 can be rejected by using a T-table

How to use a T-table?

Within the table determine the column by choosing a P-value (usually 0.05).
For the row we need to decide the Degrees of Freedom (Df = N1 + N2 -2)
  • Then the T-value is higher than the value found in the T-table, H0 can be rejected.

When do we use the Chi-squared test and what is its purpose?

Used to determine whether there is a significant difference between the expected frequencies and the observed frequencies in one or more categories.

Purpose?
To evaluate how likely the observations that are made would be, assuming the null hypothesis is true.

What does the Chi-squared (change) test do and what is its equation?

It decides if the variation in the data is due to chance or not.

  Oi = observed data
Ei = Expected values

What is the difference between a t-test and a chi-squared test?

T-test:
  • Tests a null hypothesis about two means; most often, it tests the hypothesis that two means are equal, or that the difference between them is zero.

Chi-square test:
  • Tests a null hypothesis about the relationship between two variables.

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