2.4.3.1 Natural zatsopano

Zimene Natural mwayi pa zinthu mwachisawawa mu dziko. mwachisawawa chochitika + nthawi zonse, dongosolo deta = zachilengedwe kuyesera

Chinsinsi osapanganika zatsopano kuwapangitsa chilungamo poyerekeza ndi randomization. Komabe, nthawi zina chinachake mu dziko kuti kwenikweni kumene anthu mosintha kapena pafupifupi mosintha mankhwala osiyanasiyana. Pali zitsanzo momveka bwino njira ya ntchito zatsopano zachilengedwe amachokera kafukufuku wa Angrist (1990) kuyeza zotsatira za ntchito ya usilikali pa ndalama.

Pa nkhondo Vietnam, ndi United States kuchuluka kukula kwa asilikali ake mwa kusodza. Pofuna kusankha nzika adzatchedwa mu utumiki, boma US anakonza mpikisano. Aliyense birthdate anayimiridwa pa pepala, ndi mapepala amenewa anaikidwa lalikulu galasi mtsuko. Monga tikuonera Chithunzi 2.5, izi timitengo ta chipepala limachokera ku botolo limodzi pa nthawi kudziwa ndondomeko yomwe anyamata adzatchedwa kutumikira (atsikana anali kosamugonjera asilikali a). Zochokera zotsatira, anthu anabadwa pa September 14 anaitanidwa, anthu anabadwa pa April 24 ankatchedwa wachiwiri, ndi zina zotero. Pamapeto pake, mu mpikisano uwu, anthu anabadwa pa masiku 195 osiyanasiyana maitanidwe ku ntchito pamene anthu anabadwa pa masiku 171 sanali wotchedwa.

Chithunzi 2.5: Congressman Alexander Pirnie (R-NY) akukoka kapisozi choyamba cha bukuli Selective Service pa December 1, 1969. Joshua Angrist (1990) pamodzi ndi asilikali mpikisano ndi ndalama kafukufuku wa Administration Security Social chaka zotsatira za usilikali pa ndalama. Ichi ndi chitsanzo cha kafukufuku ntchito kuyesera zachilengedwe. Source: Wikimedia Commons

Ngakhale kuti si litakhala, ndi kusodza mpikisano ali kufanana yovuta kwa osapanganika kuyesera ankalamulira: zinthu zonse ophunzira mosintha anatumizidwa kulandira mankhwala. Pankhani ya asilikali lotale, ngati tikufuna kudziwa zotsatira za asilikali-kuvomerezeka ndi usilikali pa ndalama msika ntchito wotsatira, tingathe kuyerekezera zakambidwa anthu amene birthdates anali pansi pa mpikisano cutoff (mwachitsanzo, September 14, April 24, etc.) ndi zotsatira zake kwa anthu amene akubadwa anali pambuyo cutoff (mwachitsanzo, February 20, December 2, etc.).

Popeza kuti mankhwala a pokhala akalembetse wakhala mosintha watipatsa, titha ndiye kuyeza zotsatira za mankhwala chifukwa zotsatira chilichonse chimene wakhala anayeza. Mwachitsanzo, Angrist (1990) pamodzi zokhudza amene anali osankhidwa mwachisawawa mu kusodza ndi deta zasungidwa amene anasonkhana ndi Administration Security Social kunena kuti zasungidwa a anamenyela zoyera 15% poyerekeza ndi ndalama za ofanana sanali anamenyela . Akatswiri ena ntchito njira yomweyi poyesa komanso. Mwachitsanzo, Conley and Heerwig (2011) pamodzi zokhudza amene anali osankhidwa mwachisawawa mu bukuli deta ndi banja asonkha Survey 2000 Census ndi 2005 American Community ndipo mwapezeka kuti yaitali pambuyo kusodza, panali pang'ono yaitali zotsatira za usilikali pa zosiyanasiyana zomwe zakambidwa monga nthawi ya ulamuliro nyumba (kukhala motsutsana lendi) ndi kukhazikika zogona (mosavuta popeza anasamukira ku yapita zaka zisanu).

Chitsanzo chimenechi chikusonyeza kuti nthawi zina chikhalidwe, ndale kapena zachilengedwe mphamvu kulenga zatsopano kapena pafupi-nkhaniyi akhoza leveraged ndi ofufuza. Nthawi zambiri zatsopano achilengedwe njira yabwino amati ubale chifukwa ndi zotsatira zoikamo kumene si koyenela kapena othandiza kuthamanga osapanganika zatsopano. Izi ndi njira yofunika kuti akulitse kufananitsa wokoma deta si experimental. strategy kufufuza akhoza mwachidule ndi aone kuti pali izi:

\ [\ lemba {mwachisawawa (kapena ngati mwachisawawa) chochitika} + \ lemba {nthawi zonse, pa kafukufuku mtsinje} = \ lemba {zachilengedwe kuyesera} \ qquad (2.1) \]

Komabe, kusanthula zatsopano zachilengedwe zingakhale zovuta kwambiri. Mwachitsanzo, mu nkhani ya kusodza Vietnam, siyense amene anali kusodza-woyenera anatsirizira kutumikira (panali zosiyanasiyana osaphatikizidwamo). Ndipo pa nthawi yomweyo, anthu ena amene sanali kulemba lipoti-woyenera anadzipereka kwa utumiki. Zinali ngati m'chitsimikizo matenda a mankhwala atsopano, anthu ena mu gulu mankhwala sanatenge mankhwala awo ndi anthu ena mu gulu ulamuliro atalandira mankhwala. vuto limeneli, anaitana awiri amaganiza chosatsatira malamulo, komanso mavuto ena ambiri anafotokoza mwatsatanetsatane ena mwa kuwerenga aika kumapeto kwa nkhani ino.

Njira imene timagwiritsa ntchito mwachibadwa zikuchitika ntchito mwachisawawa poyambirira pa m'badwo digito, koma kuchuluka kwa deta wamkulu amapanga njira imeneyi osavuta ntchito. Kamodzi inu mukuzindikira ena mankhwala wakhala anatumizidwa mosintha, magwero aakulu deta angapereke deta zoterezo muthe kuyerekeza zotsatira anthu pa matenda ndi ulamuliro zinthu. Mwachitsanzo, mu kuphunzira zotsatira za asilikali ndi asilikali utumiki, Angrist ntchito mbiri zasungidwa kwa Administration Security Social; popanda deta izi zotsatira, kuphunzira sikukanakhala kotheka. Pankhaniyi, ndi Administration Security Social ndi nthawizonse pa lalikulu deta gwero. Anthu ambiri basi kwambiri anasonkhana magwero deta zilipo, tidzakhala ndi zambiri zotsatira deta kuti akhoza kuyesa zotsatira za kusintha analengedwa ndi kusintha exogenous.

Mwachitsanzo njira imeneyi mu m'badwo digito, tiyeni tikambirane Mas ndi Moretti a (2009) kafukufuku kaso pa zotsatira za anzawo pa zokolola. Ngakhale padziko izo zikhoza kuwoneka osiyana osati kuphunzira Angrist wonena za zotsatira za Vietnam Choyesera, mu dongosolo onse amatsatira chitsanzo mu Eq. 2.1.

Mas ndi Moretti anayeza mmene anzanu bwanji zokolola za antchito. Pa dzanja limodzi, kukhala ndi anzawo ntchito mwakhama chingapangitse ntchito kuonjezera zokolola zawo chifukwa cha anzawo. Kapena pa dzanja lina, olimbika anzawo chingapangitse ena ogwira ntchito ku lochedwa ngakhale kwambiri. Njira momveka bwino kuphunzira zotsatira za anzawo pa zokolola adzakhala osapanganika ankalamulira kuyesera ogwira ntchito ndi mosintha anatumizidwa mosinthana ndi antchito a magulu zokolola ndipo chifukwa zokolola chimaonekera aliyense. Akatswiri Komabe, simungapeze ndandanda anthu ogwira ntchito iliyonse weniweni, ndipo Mas ndi Moretti anali kudalira kafukufuku wa zachilengedwe zimene zinachitika m'sitolo.

Ngati Eq. 2.1, kuphunzira anali magawo awiri. Choyamba, iwo ntchito nkhuni pa dongosolo golosale potuluka ndi yeniyeni, payekha, ndi nthawizonse pa muyeso wa zokolola: chiwerengero cha zinthu scanned pa mphindi. Ndipo, kachiwiri, chifukwa cha zimene ndandanda chidachitika pa golosale izi, ali pafupi mwachisawawa zikuchokera anzawo. M'mawu ena, ngakhale ndandanda wa olandira ndalama si mtima ndi njuga, ndi kwenikweni mwachisawawa. Zochita chidaliro tili mu zatsopano zachilengedwe nthawi zambiri kumadalira pa ponena za ichi "monga ngati" amanena mwachisawawa. Masuku pamutu kusintha zimenezi mwachisawawa, Mas ndi Moretti anapeza kuti ntchito ndi achinyamata zokolola apamwamba kumawonjezera zokolola. Komanso, Mas ndi Moretti ntchito kukula ndi kuchuluka kwa gulu lazidziwitso awo kusuntha kupitirira chiwerengero cha chifukwa ndi zotsatira kufufuza nkhani ziwiri zofunika kwambiri ndiponso zobisika: heterogeneity ya amenewa (umene yonse ya ogwira ntchito ndi zotsatira zikuluzikulu) ndi limagwirira kumbuyo zotsatira (n'chifukwa chiyani kukhala mkulu anzawo zokolola kuyambitsa zokolola apamwamba). Ife tidzabwerera ku awiriwa zofunika nkhani-heterogeneity za kuipa mankhwala ndi njira mu Chapter 5 tikamakambirana zatsopano zambiri.

Generalizing ku maphunziro a mphamvu ya Choyesera Vietnam pa zasungidwa ndi kuphunzira mmene amayendera pa zokolola, Table 2.3 mwachidule maphunziro ena kuti ichi yeniyeni dongosolo yemweyo: pogwiritsa ntchito nthawi zonse zochokera deta kuyeza mmene zinthu zina . Monga Table 2.3 momveka bwino kuti kafukufuku achilengedwe kulikonse ngati inu mukudziwa momwe kuyang'ana kwa iwo.

Zochita ofufuza ntchito njira zosiyana kupeza zatsopano achilengedwe, ndi amene angathe kukhala obala zipatso. Akatswiri ena kuyamba ndi nthawizonse pa deta gwero ndi kuyang'ana zinthu mwachisawawa mu dziko; ena amayamba ndi zinthu mwachisawawa m'dzikoli ndi kupeza magwero deta kuti kugwila zimakhudza awo. Pomaliza, zindikirani kuti mphamvu zatsopano achilengedwe amabwera osati kuchokera kudziŵa za kuwunika zowerengera, koma chisamaliro akulitse chilungamo poyerekeza analengedwa ndi ngozi mwayi wa mbiri.