;Approach;Strengths;Weaknesses "Unit value transfer";"Select appropriate values from existing primary valuation studies for similar ecosystems and socio-economic contexts. Adjust unit values to reflect differences between study and policy sites (usually for income and price levels).";Simple;"Unlikely to be able to account for all factors that determine differences in values between study and policy sites. Value information for highly similar sites is rarely available." "Value function transfer";"Use a value function derived from a primary valuation study to estimate ES values at policy site(s).";"Allows differences between study and policy sites to be controlled for (e.g. differences in population characteristics).";"Requires detailed information on the characteristics of policy site(s)." "Meta-analytic function transfer";"Use a value function estimated from the results of multiple primary studies to estimate ES values at policy site(s).";"Allows differences between study and policy sites to be controlled for (e.g. differences in population characteristics, area of ecosystem, abundance of substitutes etc.). Practical for consistently valuing large numbers of policy sites.";"Requires detailed information on the characteristics of policy site(s). Analytically complex."