2.4.3 Approximating gwajen

Za mu iya kimanta gwaje-gwajen da ba mu da shi ko baza muyi ba. Hanyoyi guda biyu da suka amfana daga manyan bayanai sune gwaje-gwaje na halitta da daidaitawa.

Wasu tambayoyi masu ilimin kimiyya da kuma manufofin ƙaddamarwa suna haifarwa. Alal misali, menene sakamakon aikin horon aikin aiki a kan albashi? Wani mai bincike da yake ƙoƙari ya amsa wannan tambaya zai iya kwatanta yawan kuɗin da mutanen da suka sanya hannu don horo ga waɗanda basu yi wannan ba. Amma yaya nauyin bambancin da ke tsakanin wadannan kungiyoyi ne saboda horo kuma nawa ne saboda bambance-bambancen da ke tsakanin mutane da suka sa hannu da wadanda basu yi ba? Wannan tambaya ce mai wuya, kuma wannan shine wanda ba ya tafi ta atomatik tare da ƙarin bayanai. A wasu kalmomi, damuwa game da yiwuwar bambancin bambancin da ke tattare da shi ya fito ko ta yaya ma'aikata suke cikin bayananku.

A lokuta da yawa, hanya mafi karfi da za a iya kwatanta sakamakon tasirin wasu, irin su horar da aiki, shine don gudanar da gwajin gwajin da bazuwar inda wani mai bincike ya ba da magani ga wasu mutane ba tare da wasu ba. Zan gabatar da dukkanin sura ta 4 don gwaje-gwajen, don haka a nan zan mayar da hankali ga dabarun da za a iya amfani dashi tare da bayanan gwaji. Na farko dabarun ya dogara da neman wani abu da ke faruwa a duniya cewa bazuwar (ko kusan babu wata) ya ba da magani ga wasu mutane ba wasu. Hanya na biyu ya dogara ne akan daidaitaccen tsarin daidaitaccen bayanan gwaji a cikin ƙoƙari na lissafin bambance-bambance tsakanin wadanda suka yi kuma basu karbi magani ba.

Kwararre na iya yin iƙirarin cewa an dakatar da dukkanin wadannan hanyoyi saboda suna buƙatar ra'ayi mai karfi, tsammanin da suke da wuyar ganewa kuma cewa, a aikace, an saba sabawa. Duk da yake ina jin daɗin wannan da'awar, ina tsammanin wannan ya wuce. Gaskiya ne cewa yana da wuya a dogara da ƙididdigar lamarin daga bayanan gwaji, amma ban tsammanin wannan yana nufin cewa kada muyi kokarin gwadawa ba. Musamman, hanyoyin da ba na gwaji ba zasu iya taimakawa idan ƙuntatawa na lodo ya hana ka gudanar da gwaji ko kuma idan ƙuntataccen ma'anar yana nufin ba ka so ka gudanar da gwaji. Bugu da ari, ƙwarewar gwaji ba zai iya taimakawa idan kuna so suyi amfani da bayanan da suka wanzu don tsara tsarin gwajin gwagwarmaya.

Kafin a ci gaba, yana da kyau a lura cewa yin ƙaddamar da ƙaddarar abu ɗaya shine ɗaya daga cikin batutuwa masu rikitarwa a binciken bincike na zamantakewa, kuma wanda zai iya haifar da muhawara da kuma motsa jiki. A cikin abin da ya biyo baya, zan ba da cikakken ra'ayi game da kowace hanya don gina ilmantarwa game da shi, sa'an nan kuma zan bayyana wasu kalubale da suke tasowa lokacin amfani da wannan tsarin. Ƙarin bayani game da kowane samfurin yana samuwa a cikin kayan da ke ƙarshen wannan babi. Idan kun yi niyyar yin amfani da waɗannan hanyoyi a cikin bincikenku, ina bayar da shawarar sosai don karanta ɗayan littattafai masu kyau a kan ƙididdigar ƙira (Imbens and Rubin 2015; Pearl 2009; Morgan and Winship 2014) .

Ɗaya daga cikin hanyoyin da za a samar da ƙayyadaddun ƙari daga bayanai marasa gwaji shine neman wani abu wanda ya ba da izini ga wasu mutane ba da gangan ba ga wasu. Wadannan yanayi ana kiransu gwaji na halitta . Daya daga cikin misalai mafi kyau daga gwaji na halitta ya fito ne daga nazarin Joshua Angrist (1990) yana auna sakamakon aikin soja a kan samun kuɗi. A yayin yakin da aka yi a Vietnam, Amurka ta karu da yawan mayakanta ta hanyar daftarin aiki. Don yanke shawarar wanda za a kira 'yan ƙasa zuwa sabis, Gwamnatin Amirka ta gudanar da irin caca. Kowane ranar haihuwar da aka rubuta a kan takarda, kuma, kamar yadda aka nuna a cikin adadi na 2.7, waɗannan ɗayan takarda sun zaɓa ɗaya a lokaci domin sanin abin da za a kira matasa don su yi hidima (matasan mata ba su kasance ba zuwa daftarin). Bisa ga sakamakon, mutanen da aka haifa a ranar 14 ga watan Satumba an kira su ne na farko, mutanen da aka haifa a ranar 24 ga Afrilu aka kira na biyu, da sauransu. Daga qarshe, a cikin wannan irin caca, mutane da aka haife su a cikin kwanaki 195 sune, yayin da mutane da aka haifa a cikin kwanaki 171 ba.

Figure 2.7: Babban jami'in majalisa Alexander Pirnie (R-NY) ya zana hoton farko ga jerin sashin Zaɓuɓɓuka a ranar 1 ga watan Disamba, 1969. Joshua Angrist (1990) ya haɗu da wannan irin caca tare da samun kuɗi daga Hukumar Tsaron Tsaro don kwatanta sakamakon aikin soja a kan albashi. Wannan misali ne na bincike ta amfani da gwaji na halitta. Source: Hukumar Zaɓin Zaɓin Ƙasar Amirka (1969) / Wikimedia Commons.

Figure 2.7: Babban jami'in majalisa Alexander Pirnie (R-NY) ya zana hoton farko ga jerin sashin Zaɓuɓɓuka a ranar 1 ga watan Disamba, 1969. Joshua Angrist (1990) haɗu da wannan irin caca tare da samun kuɗi daga Hukumar Tsaron Tsaro don kwatanta sakamakon aikin soja a kan albashi. Wannan misali ne na bincike ta amfani da gwaji na halitta. Source: Sashen Zaɓin Zaɓin Yankin Amirka (1969) / Wikimedia Commons .

Kodayake ba za'a bayyana ba a fili, wani irin caca na da irin mummunan kama da gwajin gwajin da bazuwar ciki: a cikin duka yanayi, ana ba da izini ga mahalarta don karɓar magani. Don nazarin tasirin wannan magani na bazuwar, Angrist yayi amfani da tsarin tsarin bayanai na yau da kullum: Gwamnatin Amirka ta Tsaron Tsaron Tsaro, wanda ke tattara bayanai game da yawancin abubuwan da Amurka ke samu daga aikin aiki. Ta hanyar hada bayanai game da wanda aka zaba a cikin jerin irin caca tare da bayanan kuɗi da aka tattara a cikin tarihin gwamnati, Angrist ya kammala cewa yawan kuɗin da tsofaffin tsofaffin ma'aikata suka samu ya kai kimanin 15% ba tare da karbar kuɗi na marasa tsohuwar ba.

Kamar yadda wannan misalin ya kwatanta, wani lokacin zamantakewa, siyasa, ko kuma dabi'un dabi'a sun sanya magunguna a hanyar da masu bincike za su iya haɓaka, kuma wani lokaci ma ana samun tasirin wadannan jiyya a kullum a kan manyan bayanan bayanan. Wannan rukunin bincike za a iya taƙaita shi kamar haka: \[\text{random (or as if random) variation} + \text{always-on data} = \text{natural experiment}\]

Don kwatanta wannan tsari a cikin zamani na zamani, bari mu bincika nazarin da Alexandre Mas da Enrico Moretti (2009) suka yi don gwada tasirin aiki tare da abokan aiki a kan ƙwarewar ma'aikacin. Kafin ganin sakamakon, yana da kyau a nuna cewa akwai tsammanin tsammanin tsammanin za ku iya samun. A gefe ɗaya, zaku iya tsammanin yin aiki tare da abokan aiki masu aiki zai jagoranci ma'aikaci don ƙara yawan yawan amfaninta saboda matsa lamba na matasa. Ko kuma, a wani bangaren, za ku iya tsammanin cewa samun abokan aiki masu wahala zasu iya jagorantar ma'aikaci don ya rabu saboda aikinsa zai kasance da abokansa. Hanyar da ta fi dacewa don nazarin ilimin matasa zai haifar da gwagwarmayar gwajin da bazuwar inda aka sanya ma'aikata ba tare da izini ba tare da ma'aikata masu nauyin samfurori daban-daban sannan kuma ana ƙayyade yawan samuwa ga kowa. Masu bincike, duk da haka, ba su kula da tsarin ma'aikata a cikin wani kasuwanci ba, don haka Mas da Moretti sun dogara ga gwaji na gwaji da suka hada da tsabar kuɗi a babban ɗaki.

A cikin wannan mahimmanci, saboda hanyar da aka tsara da kuma hanyar da aka canza, kowanne mai siya yana da ma'aikata daban daban a lokutan daban-daban. Bugu da ari, a cikin wannan mahimmanci na musamman, aikin da aka ba da kuɗi ba shi da alaƙa da yawancin 'yan uwansu ko yadda aiki yake. A wasu kalmomi, kodayake ba'a ƙaddamar da tsarin caca na caca ba, yana da kamar idan an yi amfani da ma'aikatan ba tare da izinin yin aiki tare da ƙwararru masu yawa (ko low) ba. Abin farin ciki, wannan babban kanti yana da tsarin tsarar kudi na dijital wanda ya kalli abubuwan da kowanne mai karbar ke dubawa a kowane lokaci. Daga wannan jigon bayanan rajistan ayyukan, Mas da Moretti sun iya kirkiro daidai, mutum, da kuma kullum-akan ma'auni na yawan aiki: adadin abubuwan da aka lakafta ta biyu. Hada waɗannan abubuwa biyu-sauye-sauye na yanayi a yawan ƙwarewar yara da kuma ma'auni na yawan aiki-Mas da Moretti sun kiyasta cewa idan aka sanya ma'aikacin ma'aikata masu aiki 10% fiye da matsakaici, yawan amfaninta zai karu da 1.5% . Bugu da ari, sun yi amfani da girman da wadataccen bayanan su don gano muhimman al'amurra guda biyu: bambancin wannan sakamako (wace irin ma'aikata ne ya fi girma?) Da kuma hanyoyin da ke faruwa (Me ya sa samun takwarorinsu masu yawa na haifar da su? mafi girma yawan aiki?). Za mu koma ga waɗannan muhimman al'amurra guda biyu - mahallin maganin jiyya da kuma kayan aiki-a babi na 4 idan muka tattauna gwaje-gwajen a cikin cikakken bayani.

Komawa daga waɗannan binciken biyu, tebur na 2.3 ya taƙaita sauran nazarin da ke da wannan tsarin: yin amfani da tushen bayanan da kullum don auna sakamako na wasu canje-canje bazuwar. A aikace, masu bincike suna amfani da hanyoyi daban-daban guda biyu don neman gwaji na halitta, duka biyu na iya haifar da ƙwaya. Wasu masu bincike sun fara da bayanan bayanan bayanai kuma suna neman abubuwan bazuwar a duniya; wasu fara wani taron bazuwar a duniya kuma suna neman samfurin bayanan da suka kama tasirin.

Table 2.3: Misalan gwaje-gwaje na al'ada Yin Amfani da Bayanan Girma
Ƙaddamar da hankali Source na gwaji na gwaji Mahimman bayanai a duk lokacin da Magana
Hoto tasiri akan yawan aiki Shirya tsari Lambar biya Mas and Moretti (2009)
Amincewa da abokai Hurricanes Facebook Phan and Airoldi (2015)
Yada kwakwalwa Rain Facebook Lorenzo Coviello et al. (2014)
Harkokin tattalin arziki nagari-da-peer Girgizar Kasa Bayanan kudi na wayar hannu Blumenstock, Fafchamps, and Eagle (2011)
Abun halaye na mutum 2013 Gwamnatin Amirka ta dakatar da shi Bayanan kudi na sirri Baker and Yannelis (2015)
Harkokin tattalin arziki na tsarin masu bada shawara Daban-daban Bayanin binciken a Amazon Sharma, Hofman, and Watts (2015)
Halin damuwa akan jariran da ba a haifa ba 2006-Hezbollah yaki Rubutun haihuwa Torche and Shwed (2015)
Ayyukan karatun akan Wikipedia Sauran ayoyi Shafuka na Wikipedia Penney (2016)
Abokan hulɗa a kan motsa jiki Weather Masu waƙa Aral and Nicolaides (2017)

A cikin tattaunawa har yanzu game da gwaje-gwaje na al'ada, na bar wata muhimmiyar mahimmanci: barin irin abin da kuke bayarwa ga abin da kuke so a wani lokacin yana da kyau. Bari mu koma ga misali na Vietnam. A wannan yanayin, Angrist yana sha'awar kimanta sakamakon aikin soja a kan abin da ya samu. Abin takaici, aikin soja ba a ba shi ba; maimakon an tsara shi wanda aka ba shi kyauta. Duk da haka, ba duk wanda aka tsara ba ya yi aiki (akwai wasu nau'o'i dabam-dabam), kuma ba kowa ya yi aiki ba (mutane zasu iya bayar da gudummawa don aiki). Saboda an ba da takardun izini, wani mai bincike zai iya kimanta sakamakon aikin da aka tsara ga dukan mutane a cikin wannan littafin. Amma Angrist ba ya so ya san sakamakon yin aiki; ya so ya san sakamakon aikin soja. Don yin wannan ƙayyadaddun, duk da haka, ana buƙatar ƙarin tunani da rikitarwa. Na farko, masu bincike sunyi zaton cewa hanya daya da aka tsara ta hanyar samun gagarumin tasiri shi ne ta hanyar aikin soja, wani zato da ake kira ƙuntatawa . Wannan zato yana iya zama kuskure idan, misali, mutanen da aka tsara sun kasance a cikin makaranta ya fi tsayi don kaucewa yin hidima ko kuma idan masu daukan ma'aikata ba su iya hayan mutanen da aka tsara. Gaba ɗaya, ƙuntatawar cirewa shine tsinkaye mai ma'ana, kuma yana da wuya a tabbatar da shi. Ko da kullun ƙuntatawa daidai ne, har yanzu ba zai iya yiwuwa a kimanta tasirin sabis a kan dukan mutane ba. Maimakon haka, yana nuna cewa masu bincike zasu iya kwatanta tasiri kan takamaiman mazajen da ake kira compliers (maza da za su bauta wa lokacin da aka tsara su, amma ba za su yi aiki ba idan ba a rubuta su ba) (Angrist, Imbens, and Rubin 1996) . Har ila yau, ba su kasance asalin asalin sha'awa ba. Ka lura cewa waɗannan matsalolin sun tashi ko da a cikin yanayin da aka yi da tsabta game da irin caca. Ƙarin ƙarin rikice-rikice yakan tashi lokacin da caca ta jiki ba ta sanya magani ba. Alal misali, a binciken Mas da Moretti na tsabar kudi, wasu tambayoyin sun fito ne game da zato cewa aikin abokan aiki ba shi da ƙari. Idan wannan zato yana da mummunan keta, zai iya yin la'akari da kiyasta. A ƙarshe, gwaje-gwaje na halitta na iya zama wata hanya mai karfi don samar da ƙayyadaddun ƙari daga bayanai marasa gwaji, kuma manyan kafofin watsa labarai sun kara karfin mu na karuwa akan gwaje-gwaje na halitta lokacin da suke faruwa. Duk da haka, tabbas zai buƙaci kulawa mai yawa-da kuma wasu maƙirarin tunani-don zuwa daga irin yanayin da ya bayar zuwa kimantawa da kake so.

Hanya na biyu ina so in gaya muku game da yin ƙayyadaddun ƙari daga bayanan gwaji ba ya dogara da daidaitaccen tsarin daidaitawa na marasa gwaji a cikin ƙoƙari na lissafi don bambancin da ke tsakanin waɗanda suka yi da basu karbi magani ba. Akwai hanyoyi masu yawa irin wannan gyare-gyare, amma zan mayar da hankali ga wanda ake kira matching . Idan yayi daidai, mai binciken ya dubi bayanan gwaji don ƙirƙirar nau'i na mutanen da suke kama da wanda ya karbi magani kuma wanda bai samu ba. A tsarin matching, masu bincike ne ainihin kuma pruning ; wato, watsar da lokuta inda babu matsala. Saboda haka, wannan hanya za a fi dacewa da ake kira daidai-da-pruning, amma zan tsaya tare da lokacin gargajiya: daidaitawa.

Ɗaya daga cikin misalai na ikon hanyoyin da suka dace tare da manyan bayanan da ba na gwaji ba sun fito ne daga bincike game da halayyar mai amfani da Liran Einav da abokan aiki (2015) . Suna da sha'awar yin amfani da su a kan eBay, kuma a cikin bayanin aikin su, zan mayar da hankali game da sakamakon farashin fara farashi akan sakamako masu ma'ana, irin su farashi mai sayarwa ko yiwuwar sayarwa.

Hanyar mafi mahimmanci don kimanta sakamako na fara farashi a kan farashi mai sayarwa zai kasance kawai don lissafin farashin karshe na auctions tare da farashin farawa. Wannan tsarin zai kasance lafiya idan kuna son hango farashin farashi wanda aka ba farashin farawa. Amma idan tambayarka ya shafi hadarin farashin farawa, to wannan kuskure ba zai aiki ba domin ba a dogara ne da kwatancin gaskiya ba; ƙaura tare da farashin fara farashi zai iya bambanta da waɗanda suke da farashin haɓaka masu girma (misali, suna iya zama daban-daban na kayan kaya ko sun haɗa da irin masu sayarwa).

Idan kun rigaya ku san matsalolin da za su iya tashi yayin da za ku iya ƙaddamar da ƙaddara daga bayanan marasa gwaji, kuna iya tsayar da ƙwaƙwalwar ƙwaƙwalwa kuma ku yi la'akari da gudana a gwaje-gwajen filin inda za ku sayar da wani abu mai faɗi, kungiya ta golf - tare da gyara saiti na siginan siginar-ce, kyauta kyauta da kuma siyar bude ga makonni biyu-amma tare da baƙi sanya farashin farashin. Ta hanyar kwatanta sakamakon kasuwancin da aka samu, wannan gwajin filin zai ba da cikakken fahimtar sakamako na fara farashin farashi. Amma wannan nauyin zai shafi takamaiman samfurin da aka saita na sigogi masu siya. Sakamakon zai iya zama daban-daban, alal misali, don daban-daban samfurori. Ba tare da karfi da ka'idar ba, yana da wuyar ƙwarewa daga wannan gwajin guda ɗaya zuwa cikakken jigilar gwaje-gwajen da za a iya gudanar. Bugu da ƙari, gwaje-gwaje na filin ƙanshi yana da tsada sosai cewa ba zai yiwu ba don gudanar da kowane bambancin da za ku iya gwadawa.

Ya bambanta da hanyoyin da za a yi da kuma gwaji, Einav da abokan aiki sunyi ta uku: matching. Babban mahimmanci a cikin labarun su shine gano abubuwan da suka dace da gwaje-gwajen filin da suka faru a kan eBay. Alal misali, adadi na 2.8 ya nuna wasu daga cikin jerin labaran 31 don daidai wannan karamar golf - mai sayar da kaya mai suna Taylormade Burner 09 Driver-daidai da mai sayarwa daya- "budgetgolfer." Duk da haka, wadannan jerin sunayen 31 suna da siffofin daban-daban na daban, irin su farawa daban-daban farashin, kwanakin ƙarshe, da kuma kudade. A takaice dai, yana da kamar "budgetgolfer" yana gudanar da gwaje-gwaje don masu bincike.

Wadannan sunayen na Taylormade Burner 09 Driver da aka sayar da "budgetgolfer" suna daya misali na jerin kayan da aka dace, inda ainihin wannan abu yana sayarwa ta ainihin mai sayarwa, amma kowane lokaci tare da siffofin daban-daban daban daban. A cikin manyan akwatunan eBay akwai ƙididdigar dubban dubban matakan da suka dace tare da miliyoyin jerin. Saboda haka, maimakon kwatanta farashi na ƙarshe ga duk auctions tare da farashin da aka ba, Einav da abokan aiki idan aka kwatanta da su. Don hada haɓaka daga kwatancen da ke cikin wadannan daruruwan dubban matakan da suka dace, Einav da abokan aiki sun sake bayyana farashin farawa da farashin karshe dangane da ma'auni na ma'aunin kowane abu (misali, farashi mai sayarwa). Alal misali, idan Taylormade Burner 09 Driver yana da darajar $ 100 (dangane da tallace-tallace), to, za a bayyana farashin farko na $ 10 a matsayin 0.1 kuma farashin karshe na $ 120 a matsayin 1.2.

Figure 2.8: Misali na daidaitaccen tsari. Wannan shi ne ainihin gidan golf (Taylormade Burner 09 Driver) wanda aka sayar da shi daidai da mutum (budgetgolfer), amma wasu daga cikin wadannan tallace-tallace sun yi a karkashin yanayi daban-daban (misali, farashin farawa). Reproduced ta izinin daga Einav et al. (2015), adadi 1b.

Figure 2.8: Misali na daidaitaccen tsari. Wannan shi ne daidai wannan filin wasan golf (Taylormade Burner 09 Driver) wanda aka sayar ta daidai mutumin nan ("budgetgolfer"), amma wasu daga cikin wadannan tallace-tallace sun yi a karkashin yanayi daban-daban (misali, farashin farawa). Reproduced ta izinin daga Einav et al. (2015) , adadi 1b.

Ka tuna cewa Einav da abokan aiki suna sha'awar sakamako na fara farashi kan sakamakon sakamako. Da farko, sun yi amfani da yin amfani da layin linzamin kwamfuta don kiyasta cewa farashin mafi girma ya rage yiwuwar sayarwa, kuma mafi girma farashin farashi ƙara farashin kaya na ƙarshe (yanayin kan batun sayarwa). Da kansu, waɗannan ƙididdigar-waɗanda suke bayyana dangantaka ta linzami kuma suna da girman kai a kan dukkan kayayyakin-ba duk abin sha'awa ba ne. Bayan haka, Einav da abokan aiki sunyi amfani da girman bayanai na su don ƙirƙirar wasu ƙididdiga masu yawa. Alal misali, ta hanyar kwatanta sakamakon daban don farashin daban-daban daban, sun gano cewa dangantaka tsakanin farashin farawa da farashi mai sayarwa ba shi da alaka (adadi 2.9). Musamman ma, don fara farashin tsakanin 0.05 da 0.85, farashin farawa yana da tasiri sosai akan farashin sayarwa, abin da aka gano wanda aka bace shi ta hanyar binciken farko. Bugu da ƙari, maimakon ƙaddarawa a kan dukkan abubuwa, Einav da abokan aiki sun kiyasta tasiri na farawa farashi ga nau'o'in nau'o'i 23 (misali, kayan mai, kayan lantarki, da kuma wasanni na wasanni) (adadi na 2.10). Wadannan ƙididdiga sun nuna cewa ga abubuwa masu rarrabe-irin su farashin farawa da ƙimar da ke da ƙananan sakamako a kan yiwuwar sayarwa da kuma tasiri a kan farashi na ƙarshe. Bugu da ari, don ƙarin kayayyaki masu daraja - irin su DVDs-farashin farawa yana da kusan tasiri akan farashin karshe. A wasu kalmomi, matsakaici wanda ya hada da sakamakon daga nau'o'in 23 daban-daban suna ɓoye bambancin da ke tsakanin waɗannan abubuwa.

Figure 2.9: Sadarwar tsakanin farashin farawa da yiwuwar sayarwa (a) da farashin sayar (b). Akwai dangantaka tsakanin linzami tsakanin farashin farawa da yiwuwar sayarwa, amma dangantaka marar dangantaka tsakanin farashin farawa da farashin sayarwa; don farawa farashin tsakanin 0.05 da 0.85, farashin farawa yana da tasiri sosai akan farashin sayar. A cikin waɗannan lokuta, dangantaka ne mai mahimmanci mai mahimmanci na darajar abu. An sauya daga Einav et al. (2015), Figures 4a da 4b.

Figure 2.9: Sadarwar tsakanin farashin farawa da yiwuwar sayarwa (a) da farashin sayar (b). Akwai dangantaka tsakanin linzami tsakanin farashin farawa da yiwuwar sayarwa, amma dangantaka marar dangantaka tsakanin farashin farawa da farashin sayarwa; don farawa farashin tsakanin 0.05 da 0.85, farashin farawa yana da tasiri sosai akan farashin sayar. A cikin waɗannan lokuta, dangantaka ne mai mahimmanci mai mahimmanci na darajar abu. An sauya daga Einav et al. (2015) , Figures 4a da 4b.

Figure 2.10: Bayani daga kowane nau'i na abubuwa; Ƙarin maƙasudin shine ƙayyadaddun ga dukan ɗakunan da aka haɗa (Einav et al. 2015). Wadannan ƙididdiga sun nuna cewa don ƙarin abubuwa dabam-irin su abubuwan tunawa-farashin farawa yana da ƙananan sakamako a kan yiwuwar sayarwa (axis x) da kuma sakamako mafi girma akan farashi na ƙarshe (axis y). An sauya daga Einav et al. (2015), adadi 8.

Figure 2.10: Bayani daga kowane nau'i na abubuwa; Ƙarin maƙasudin shine ƙayyadaddun ga dukan ɗakunan da aka haɗa (Einav et al. 2015) . Wadannan ƙididdiga sun nuna cewa ga abubuwa masu rarrabe-irin su abubuwan tunawa-farashin farawa yana da ƙananan sakamako a kan yiwuwar siyarwa ( \(x\) -axis) da kuma sakamako mafi girma a farashin sayarwa na karshe ( \(y\) -axis). An sauya daga Einav et al. (2015) , adadi 8.

Duk da cewa ba ka da sha'awar yin amfani da su a kan eBay, dole ka yi sha'awar hanyar da aka kwatanta da 2.9 da kuma adadi na 2.10 suna ba da fahimtar eBay fiye da ƙididdigar sauki wanda ke kwatanta dangantaka ta haɗin linzami da kuma haɗa nau'o'in abubuwa daban-daban. Bugu da ƙari, ko da yake zai yiwu a kimiyya don samar da waɗannan ƙananan ƙididdiga da gwaje-gwajen gwaje-gwaje, kudin zai sa waɗannan gwaje-gwaje da wuya.

Kamar yadda gwaji na halitta, akwai hanyoyi da dama da suka dace zasu iya haifar da mummunan kimantawa. Ina tsammanin babban damuwa da matakan da aka kwatanta shi ne cewa za a iya jin dadin su ta hanyar abubuwan da ba a yi amfani dashi ba. Alal misali, a cikin mahimman sakamako, Einav da abokan aiki sunyi daidai da halayen hudu: lambar ID mai sayarwa, ƙunshiyar abu, abu abu, da kuma maƙallan. Idan abubuwa sun bambanta a hanyoyi waɗanda ba a yi amfani da shi ba don daidaitawa, to wannan zai iya haifar da rashin daidaito. Alal misali, idan "budgetgolfer" ya saukar da farashi ga Taylormade Burner 09 Driver a cikin hunturu (lokacin da kungiyoyin golf ba su da shahararren), sa'an nan kuma zai iya bayyana cewa farashin fara farashin zai kai ga farashin karshe, idan a gaskiya wannan zai zama wani abu na sauya yanayi a buƙata. Wata hanya ta magance wannan damuwa ita ce ƙoƙari da yawa daban-daban. Alal misali, Einav da abokan aiki sun sake maimaita nazarin su yayin da suke canza lokacin da aka yi amfani dasu don daidaitawa (matakan da aka haɗa sun haɗa da abubuwa a sayarwa a cikin shekara guda, cikin wata daya, da kuma lokaci-lokaci). Abin farin ciki, sun sami irin wannan sakamako na duk lokacin windows. Ƙarin damuwa da daidaituwa ya fito ne daga fassarar. Ƙididdiga daga daidaitawa kawai yana amfani da bayanai masu dacewa; ba su shafi sharuɗɗan da ba za a iya daidaita su ba. Alal misali, ta hanyar taƙaita binciken su ga abubuwa da ke da jerin lambobi, Einav da abokan aiki suna mai da hankali ga masu sana'a da masu sana'a. Saboda haka, lokacin da aka fassara waɗannan kwatancin dole ne mu tuna cewa suna amfani da wannan sashin na eBay kawai.

Daidaita wata hanya ce mai mahimmanci don neman daidaito mai kyau a cikin bayanan gwaji. Ga yawancin masana kimiyyar zamantakewa, daidaituwa yana jin dashi mafi kyau ga gwaje-gwajen, amma wannan shine imani da za a iya bita, dan kadan. Daidaita a cikin bayanai mai zurfi na iya zama mafi alhẽri fiye da ƙananan gwaje-gwaje na gwaje-gwaje a yayin da (1) mahallin abubuwa ke da muhimmanci kuma (2) an auna mahimmancin mahimmanci da ake buƙata don daidaitawa. Table 2.4 yana bayar da wasu misalan yadda za a iya amfani da daidaituwa tare da manyan asusun bayanai.

Table 2.4: Misalan Nazarin da Suka Yi Amfani da Babban Bayanan Bayanan
Ƙaddamar da hankali Babban bayanan bayanai Magana
Hanyoyin harbe-harbe a kan tashin hankalin 'yan sanda Bayanan dakatarwar da-frisk Legewie (2016)
Tasirin Satumba 11, 2001 akan iyalai da maƙwabta Rubutun kisa da takardun kyauta Hersh (2013)
Taron jama'a Sadarwa da samfurori da aka samo asali Aral, Muchnik, and Sundararajan (2009)

A ƙarshe, ƙididdigar hadarin causal daga magungunan gwaji ba wuya, amma ana iya amfani da hanyoyi irin su gwaje-gwaje na al'ada da gyare-gyare na statistical (misali, matching). A wasu yanayi, waɗannan hanyoyi na iya zama mummunan kuskure, amma idan aka sanya su a hankali, waɗannan hanyoyi zasu iya zama da amfani ga tsarin gwajin da na bayyana a babi na 4. Bugu da ƙari, waɗannan hanyoyi guda biyu suna da alamar ƙila su amfana daga ci gaba da koyaushe- kan, manyan bayanai.