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rchi-squaredcontingency

Randomization check

I feel a little stupid for asking this question, but somehow I can't figure it out!

I am trying to see if participants are equally randomly assigned to two groups, so the contingency table looks like the below

Condition A    Condition B
30                40

The main data look like the one below

    Variable 1
P1   Condition A
P2   Condition B
P3   Condition A
P4   Condition A
P5   Condition B
P6   Condition A
.        .
.        .
.        .

What would be the best way/function to check (using R) that they were equally distributed to either of the conditions?

Thank you a lot!

Solution

  • You want a chisq.test(), which operates on a contingency table, not the raw vector of groups. The usage is simply like this:

    > x = factor(sample(c('A', 'B'), 1000, replace = TRUE, prob = c(0.6, 0.4)))
> table(x)
x
  A   B
605 395
> chisq.test(table(x))

    Chi-squared test for given probabilities

data:  table(x)
X-squared = 44.1, df = 1, p-value = 3.12e-11