Table 1 Descriptive characteristics of selected studies (n = 78)
Variable | Number of studies | Frequency (%) |
|---|---|---|
Study design | ||
Studies with a comparator group | 9 | 11.5 |
Studies without a comparator group | 69 | 88.5 |
Type of impact reported | ||
Studies that only report mortality impact | 71 | 91.0 |
Studies that only report productivity impact | 6 | 7.7 |
Studies that report mortality and productivity impacts | 1 | 1.3 |
Type of cause reported | ||
Studies that only report infectious cause(s) | 50 | 64.1 |
Bacteria | 5 | 10.0 |
Virus | 19 | 38.0 |
Parasite | 18 | 36.0 |
Fungus | 0 | 0.0 |
Mix | 8 | 16.0 |
Studies that only report non-infectious cause(s) | 20 | 25.6 |
Injuries/accidents | 1 | 5.0 |
Predation | 11 | 55.0 |
Nutritional deficit | 1 | 5.0 |
Mix (poisoning, predation, injury/accidents, harsh weather) | 7 | 35.0 |
Studies that report infectious and non-infectious cause (s) | 8 | 10.3 |
Number of disease(s)/condition(s) reported | ||
Studies that report impact on one disease/condition | 53 | 67.9 |
Studies that report impact on two disease(s)/condition(s) | 12 | 15.4 |
Studies that report impact on three disease(s)/condition(s) | 7 | 9.0 |
Studies that report impact on four or more disease(s)/condition(s) | 6 | 7.7 |
Duration of data collection | ||
Studies that collect data < 5 months (20 weeks) | 44 | 56.4 |
Studies that collect data 6–12 months (21–51 weeks) | 10 | 12.8 |
Studies that collect data ≥ 12 months (≥ 52 weeks) | 24 | 30.8 |
Farm data quantified | ||
Studies that quantify farm outputs | 73 | 93.6 |
Studies that quantify farm inputs and outputs | 5 | 6.4 |
Number of chickens included in the study | ||
≤50 | 5 | 6.4 |
51–200 | 10 | 12.8 |
201–1000 | 26 | 33.4 |
1001–1999 | 4 | 5.1 |
2000–4000 | 18 | 23.1 |
≥4000 | 14 | 17.9 |
NA | 1 | 1.3 |