Document Sample

c8a2f93f-2cd0-4cde-8f4a-bc627616331a.xls Number Needed to Protect (NNP.xl4) Calculator (Absolute Risk Production) Clinical Decision Making Program Department of Family Medicine, University of Oklahoma Health Sciences Center Many studies talk about the relative risk or risk ratio of being exposed, versus not exposed, to an entity such as a chemical or toxin or food or drug. This is the rate of a bad outcome among those exposed, divided by the rate among those not exposed. The problem is that equal risk rates will have different impacts depending on how rare the outcome is. An example is a statement in Science in 1995: Epidemiologists do not take a reported risk seriously unless there is a risk ratio of at least 3. The solution is to produce the absolute risk production (akin to the absolute risk reduction for treatments) and the Number Needed to Protect (analogue of the number needed to treat). How many people do we need to protect in order to prevent one adverse outcome? To do this we need information on the number of people who have bad outcomes with and without the exposure. This spreadsheet will calculate the Number Needed to Protect given raw data, risk ratio, and odds ratio. Raw Data Input Page 2 Risk Ratio Input Page 3 Odds Ratio Input Page 4 Case/Control Data Page 5 Page 1 c8a2f93f-2cd0-4cde-8f4a-bc627616331a.xls Page 2 If the data come in the form of counts of patients who got, and did not get, the adverse reaction, in a population based study or randomized controlled trial, fill those in here and results will appear in the tables below. Outcome: Adverse Good Rate Exposed to risk factor 300 300 0.500 Not exposed 700 750 0.483 No Exposure Exposure Relative Absolute Number needed Risk to Risk Production protect NE E E/NE E-NE 1/ARP 0.483 0.500 1.036 0.017 58.000 Adverse No adverse Outcome Outcome a b a+b Exposure 300 300 600 c d c+d No exposure 700 750 1450 a+c b+d a+b+c+d (Other options 1000 1050 2050 below) Correlation: Phi Coefficient (or "r") r= 0.016 (ad-bc)/sqrt[(a+b)(c+d)(a+c)(b+d)] r2 = 0.000 Yule's Q Q = (ad-bc)/(ad+bc) Q= 0.034 Standardized increment SI = (p2-p1)/sqrt(PQ) SI = 0.034 = (a/(a+b) - c/(c+d))/sqrt((a+c)/N)*(b+d)/N)) where N = a+b+c+d Rate Ratio RR =[a/(a+b)]/[c/(c+d)] RR = 1.036 Odds Ratio OR = ad/bc OR = 1.071 L Log Odds Ratioog OR = log a + log d - log b - log c Log OR = 0.030 Rate Difference RD = a/(a+b) - c/(c+d) Disease rate increases from 0.482759 to 0.500000 due to exposure, for a gain of RD = 0.017241 Page 2 c8a2f93f-2cd0-4cde-8f4a-bc627616331a.xls Page 3 If the data come in the form of risk ratio, plus the risk for unexposed, then give that and we will construct the table of counts. Reported risk ratio 1.01 Reported or est risk for the unexposed 0.5 Number of people/categ: 1000 Outcome: Adverse Good Rate Exposed to risk factor 505 495 0.505 Not exposed 500 500 0.500 No Exposure Exposure Relative Absolute Number needed Risk to Risk Production protect NE E E/NE E-NE 1/ARP 0.500 0.505 1.010 0.005 200.000 Page 3 c8a2f93f-2cd0-4cde-8f4a-bc627616331a.xls Page 4 If the data come in the form of odds ratio, plus the odds for unexposed, then give that and we will construct the table of counts. Reported odds ratio 5 Reported or est odds for the unexposed 8 Number of people/categ: 1000 Outcome: # adverse for unexposed = (OUE/(1-OUE))*N Adverse Good Rate Odds # good for unexposed = N - (OUE/(1-OUE))*N Exposed to risk factor 975.6 24.4 0.976 40 # adverse for exposed = OR*OUE*N/(1 + OR*OUE) Not exposed 888.9 111.1 0.889 8 # good for exposed = N - OR*OUE*N/(1 + OR*OUE) No Exposure Exposure Relative Absolute Number needed Risk to Risk Production protect NE E E/NE E-NE 1/ARP 0.889 0.976 1.098 0.087 11.531 Page 4 c8a2f93f-2cd0-4cde-8f4a-bc627616331a.xls Page 5 If the data come in the form of counts of patients who got, and did not get, the adverse reaction, in a case/control study, fill those in here and results will appear in the tables below. Cases: Adverse outcome Exposed to risk factor 30 Proportion of cases exposed Not exposed 20 0.6 Controls: Adverse outcome Exposed to risk factor 20 Proportion of controls exposed Not exposed 60 0.25 Rate of adverse outcome in the population 0.5 Total number for the following table 1000 Outcome: Adverse Good Rate Exposed to risk factor 300 125 0.706 Not exposed 200 375 0.348 No Exposure Exposure Relative Absolute Number needed Risk to Risk Production protect NE E E/NE E-NE 1/ARP 0.348 0.706 2.029 0.358 2.793 Adverse No adverse Outcome Outcome a b a+b Exposure 300 125 425 c d c+d No exposure 200 375 575 a+c b+d a+b+c+d (Other options 500 500 1000 below) Correlation: Phi Coefficient (or "r") r= 0.354 (ad-bc)/sqrt[(a+b)(c+d)(a+c)(b+d)] r2 = 0.125 Yule's Q Q = (ad-bc)/(ad+bc) Q= 0.636 Standardized increment SI = (p2-p1)/sqrt(PQ) SI = 0.716 = (a/(a+b) - c/(c+d))/sqrt((a+c)/N)*(b+d)/N)) where N = a+b+c+d Rate Ratio RR =[a/(a+b)]/[c/(c+d)] RR = 2.029 Odds Ratio OR = ad/bc OR = 4.500 L Log Odds Ratioog OR = log a + log d - log b - log c Log OR = 0.653 Rate Difference RD = a/(a+b) - c/(c+d) Disease rate increases from 0.347826 to 0.705882 due to exposure, for a gain of RD = 0.358056 Page 5

DOCUMENT INFO

Shared By:

Categories:

Tags:
University of Illinois, Personal tools, twelfth letter, Event Calendar, Usage notes, dynamic portal engine, lower case, community service, free dictionary, Main Menu

Stats:

views: | 6 |

posted: | 3/8/2010 |

language: | |

pages: | 5 |

OTHER DOCS BY tyndale

Docstoc is the premier online destination to start and grow small businesses. It hosts the best quality and widest selection of professional documents (over 20 million) and resources including expert videos, articles and productivity tools to make every small business better.

Search or Browse for any specific document or resource you need for your business. Or explore our curated resources for Starting a Business, Growing a Business or for Professional Development.

Feel free to Contact Us with any questions you might have.