Why is the existence of vestigial structures significant to the study of evolution?

it's kinda really complex you have animals like snakes evolution says they used to have legs how can this be proven? This is proven by vestigial structures as some snakes like certain pythons still have legs however, they are underdeveloped and are used for nothing. Whales have pelvis bones this may not seems special but it is because every chordate that has ever walked on land has one thing in common and that's a pelvis this along with other data gathered really concrete the idea of evolution into reality

Different Measures of Disease

Question              Measure of Disease

a.                           I = incidence rate

b.                           P = prevalence

c.                           L = lifetime prevalence

d.                           L = lifetime prevalence

e.                           M = crude mortality rate

Explanation:

a) Measures of disease:

I = incidence rate (p. 126): measures the frequency of disease occurrence in a population over time. It is measured as new episodes of illness in a period divided by the population.

P = prevalence (p. 113): ratio or proportion of persons in a population with a disease at a time or over time.  It is based on a sample.

L = lifetime prevalence (p. 114):  the proportion or ratio of a population who had a disease at some point in their life.

M = crude mortality rate (crude death rate) (p. 112): the ratio of deaths in a period among a geographical population.

R = sex ratio (counts) (p. 109): ratio of male and female population.