Season Effect


This data set contains 2,919 individual records of adults undergoing colorectal surgery. Age, gender, race, BMI, several risk factors, several surgical indices, vitamin D levels (on 5% of the patients, approx.), the key predictor (season) and the outcome (infection or not) are provided. The dataset is cleaned and complete (no missing data except for vitamin D levels). There are no outliers or data problems. These are data from a study by Turan et al,  “Season and vitamin D status do not affect probability for surgical site infection after colorectal surgery”, Turan et al., 2015, European Surgery; 47(6):341-5.

Study Design Topic Statistical Method Statistical Method Statistical Method
Prospective Cohort Colorectal Surgery Contingency Tables Logistic Regression


The Season Effect dataset was contributed by David Ngendahimana, Pre-Doctoral Fellow, Case-Western Reserve University. Please refer to this resource as: David Ngendahimana, “Season Effect Dataset”, TSHS Resources Portal (2016). Available at


Colorectal surgery is associated with a high rate of surgical site infection (SSI) and occurs in 11-28% of all patients who undergo this surgery.   Variations in SSI are hypothesized to be related to season and, in particular, season-related fluctuations in vitamin D.


This study aimed to compare rates of SSI among patients having colorectal surgery in winter to those having surgery in the summer.  Additional analyses compared rates of SSI among patients with high vitamin D concentration and those with low vitamin D concentration.

Subjects & Variables

Subject # Obs # Var Introduction Data Dictionary
Season Effect 2919 14 Season Introduction Season Data Dictionary

Data Downloads

Posting Date Contributor (email)
07/14/16 David Ngendahimana (


Teaching Resources

last updated on 7/14/2016

# Name (link) Posting Date Author (email) Type Statistical Topic Level Keywords
1 Resource 01 7/14/2016 David Ngendahimana ( Homework Inference Introductory Logistic Regression