ABSTRAK
Penelitian ini bertujuan untuk mengetahui pengaruh waktu pemberian umpan balik dari penerima surat terima kasih terhadap kebahagiaan pengirimnya. Ini dilakukan untuk melanjutkan penelitian sebelumnya yang menunjukkan bahwa menulis surat terima kasih dapat meningkatkan kebahagiaan (Seligman et al., 2005; Toepfer et al. 2012), tetapi belum meneliti pengaruh waktu pemberian umpan balik dari penerima surat. Partisipan sejumlah 45 mahasiswa diminta membuat serta menyampaikan satu surat terima kasih setiap pekannya selama tiga minggu dan secara acak dibagi ke dalam dua kelompok berdasarkan waktu pemberian umpan balik dari penerima surat, yakni kelompok umpan balik langsung (n = 22) dan tertunda (n = 23). Hasil penelitian mendukung hipotesis, yakni peningkatan kebahagiaan dari saat sebelum dan setelah periode penelitian pada kelompok umpan balik langsung lebih tinggi secara signifikan dibandingkan kelompok umpan balik tertunda, t (43) = 2,207, p < 0,05 (one-tailed), r2 = 0,1017. Dibandingkan umpan balik tertunda, partisipan yang menerima umpan balik langsung terpengaruh dan mempengaruhi emosi penerima surat secara timbal balik. Partisipan juga secara segera memperoleh penguat berupa ungkapan syukur kembali dari penerima surat, sehingga berdasarkan prinsip belajar dapat meningkatkan keinginan untuk memunculkan tingkah laku yang sama di kemudian hari.

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ABSTRAK
The aim of this study is to know the effect of delayed feedback from receiver of gratitude letter towards sender?s happiness. This study is the continuation of the previous researches that showed writing a gratitude letter can increase happiness (Seligman et al., 2005; Toepfer et al. 2012), but had not yet investigated the effect of delayed feedback from receivers. 45 college participants were asked to write and deliver one gratitude letter every week for three weeks and were randomly assigned to two experimental groups based on the moment of feedback from receivers, direct (n=22) or delayed (n=23). The result of this study supports the hypothesis that the gained score of happiness of direct feedback group from before and after the experiment is higher than delayed feedback group, t (43) = 2,207, p < 0,05 (one-tailed), r2 = 0,1017. Compared to delayed feedback group, participants in direct feedback group can be affected by and influence receivers? emotion reciprocally. Participants also receive reinforcers such as expressions of gratitude in return from receivers immediately, and thus in accordance with learning principle, can increase the emergence of the same behavior in the future.