SinclairgainedacertainreputationbyaHistoryoftheRevenue1785-90，and，likeMalthus，travelledontheContinenttoimprovehisknowledge。Hisfirstbookfinished，hebeganthegreatstatisticalworkbywhichheisbestremembered。HeissaidtohaveintroducedintoEnglishthenameof’statistics，’
fortheresearchesofwhichalleconomicalwriterswerebeginningtofeelthenecessity。Hecertainlydidmuchtointroducethereality。Sinclaircirculatedanumberofqueriesupon’naturalhistory，’’population，’’productions，’
and’miscellaneous’informationstoeveryparishministerinScotland。Hesurmountedvariousjealousiesnaturallyexcited，andtheultimateresultwastheStatisticalAccountofScotlandwhichappearedintwenty-onevolumesbetween1791and1799。35*ItgivesanaccountofeveryparishinScotland，andwasofgreatvalueassupplying36*basisforallsocialinvestigations。
Sinclairboretheexpense，andgavetheprofitstothe’SonsoftheClergy。’
In1793Sinclair，whohadbeeninparliamentsince1780，madehimselfusefultoPittinconnectionwiththeissueofexchequerbillstomeetthecommercialcrisis。HebeggedinreturnforthefoundationofaBoardofAgriculture。