t-tests computation for PTSD studies

two independent sample t tests

compute pooled sd first

# provide the sd and sample sizes from each condition
s1 = 13.8;
s2 = 17.3;
n1 = 17;
n2 = 18;
  
sdp = sqrt(((n1-1)*s1^2+(n2-1)*s2^2)/(n1+n2-2)); sdp

## [1] 15.70077

compute t value

# provide mean from each condition
m1 = 36.5;
m2 = 43.9;

t.value = (m1-m2)/(sdp*(sqrt(1/n1 + 1/n2))); t.value

## [1] -1.393598

p.value = 2*pt(-abs(t.value), df=(n1+n2-2)); p.value

## [1] 0.1727545