IB ESS Key Equations

Crude birth rate (CBR)

(total births in a year / total population) x 1000

Crude death rate (CDR)

(total deaths in a year / total population) x 1000

Natural increase rate (NIR)

(CBR - CDR) / 10

Doubling time (DT)

70 / NIR (%)

Ecological footprint (EF)

total area required to sustain a population / total population size

Net primary productivity (NPP)

NPP = GPP - R

Gross secondary productivity (GSP)

Food eaten - fecal loss

Net secondary productivity (NSP)

GSP - R

Trophic level efficiency

(energy at higher trophic level / energy at lower trophic level) x 100

Biochemical oxygen demand (BOD)

Amount of dissolved oxygen needed by microorganisms to decompose organic matter (higher indicates more pollution)