Z-Skor ve Kutu Grafiğiyle Sapan Değer Belirleme

Abstract

Türkiye'deki 1926'dan 2012'ye kadar olan su kaynakları verileri hataya açıktır ve bu durum sıkı kalite kontrol prosedürlerini gerektirmektedir. 129 istasyondaki aylık ortalama sıcaklık, ortalama bağıl nem ve toplam yağış verilerindeki sapan değerler, z-skoru ve kutu grafikleri kullanılarak analiz edildi. Analiz sonuçları, mevsime özgü ön işleme prosedürlerinin uygulanmasının gerekliliğini ve sapan değer tespit sınırları arasındaki eşitsizliklerin belirgin olduğunu ortaya koymaktadır. Ayrıca, çeyrekler arası aralık için katsayı olarak dört değerinin kullanılmasının zorunluluğu vurgulanmıştır. Sapan değerlerinin, eksik verilere ve sapan olmayan değerlere, özellikle yaz aylarında sıfır olmayan yağış kayıtlarına yakın olma eğilimi göstermesi dikkat çekicidir. Sıcaklık ve yağış sapan değerlerinin mekansal ve zamansal açıdan benzerlikler gösterdiği belirlenmiştir. Bağıl nem ve yağış sapan değerlerini çıkaran komşu bölgeler arasında benzerlik gözlemlenmiştir. Çalışmada ayrıca, sapma miktarı ile sapan değer adedi arasında ters orantılı bir ilişki saptanmış olup, sapan değer içeren istasyonların bölgesel konumları ile bu istasyonlardaki verilerin dağılımları arasında anlamlı bir ilişki olduğu sonucuna varılmıştır.

Keywords

• Hidroloji
• Sapan Değer
• Z-Skor
• Kutu Grafiği.

Outlier Detection by Z-Score and Box Plot

Abstract

The water resources data from Turkey, spanning the period from 1926 to 2012, are susceptible to errors, necessitating rigorous quality control procedures. Outliers in the monthly average temperature, relative humidity, and total precipitation data from 129 stations were analysed using z-scores and box plots. The analysis revealed the necessity of applying season-specific preprocessing procedures and highlighted significant inequalities in the thresholds used for outlier detection. Additionally, it was emphasized that a coefficient of four should be used for the interquartile range. Notably, outliers tended to be close to missing data and non-outlier values, particularly to non-zero precipitation records during the summer months. Spatial and temporal similarities were observed in the temperature and precipitation outliers, while relative humidity and precipitation outliers exhibited similarities among neighbouring regions that generated outliers. The study also identified an inverse relationship between the magnitude of deviation and the frequency of outliers, and it found a significant correlation between the regional locations of stations containing outliers and the distribution of data within these stations.

Keywords

• Hydrology
• Outliers
• Z-Score
• Boxplot.

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