These ratios tell you how much the odds of a disease increase when a test is positive (LR+) or how much the odds of a disease decrease when a test is negative (LR-)
Positive likelihood ratio -– How likely is the disease present if a test is positive
- You can calculate it out from the sens/spec; LR+ = sens / (1-spec)
Negative likelihood ratio – How likely is the disease not present with a negative test
- LR− = (1-sens) / spec
This example can be seen in this article: Asciutto KC, Ernstson A, Forslund O, Borgfeldt C. Self-sampling with HPV mRNA analyses from vagina and urine compared with cervical samples. J Clin Virol. 2018 Apr;101:69-73. doi: 10.1016/j.jcv.2018.02.002. Epub 2018 Feb 6. PMID: 29433016.
|
HPV+ |
HPV- |
|
Vaginal Self Sampling + |
114 |
18 |
132 |
Vaginal Self Sampling - |
22 |
51 |
73 |
|
136 |
69 |
205 |
Positive likelihood ratio -– How likely is the disease present if a test is positive
- You can calculate it out from the sens/spec; LR+ = sens / (1-spec)
0.84/(1-0.74) = 3.23
Negative likelihood ratio – How likely is the disease not present with a negative test
- LR− = (1-sens) / spec
(1-0.84)/0.74=0.22
To gain further skill visit: http://www.cebm.utoronto.ca/practise/ca/statscal/