Most classical statistical tests assume that the data is normally distributed, ie its histogram or density curve is bell shaped with peak at center.

**code:**

> hist(bwdf$age)

**output (graph): **

**code:**

> plot(density(bwdf$age))

**output (graph): **

Following function plots 4 graphs which indicate whether the data is normally distributed or not:

**code:**

> myqq = function(vect) {

par(mfrow=c(2,2))

qqnorm(vect); qqline(vect)

plot(ecdf(vect), main = 'Cumulative Distribution Curve\n(sigmoid shape means normal distribution)')

# cumulative distribution;

hist(vect)

plot(density(vect))

}

> myqq(birthwt$age)

**output (graph): **