This prospective cohort study was used to investigate the effects of hormone replacement therapy (HRT) on coronary artery disease in post-menopausal women. Because it is a ratio and expresses how many times more probable the outcome is in the exposed group, the simplest solution is to incorporate the words "times the risk" or "times as high as" in your interpretation. Together with risk difference and odds ratio, relative risk measures the association between the exposure and the outcome. In essence, we regard the unexposed group as having 100% of the risk and express the exposed group relative to that. Conversely, in the aspirin study it is not correct to say that those on aspirin had 0.57 times less risk (wrong). Date last modified: March 19, 2018. Odds ratios and relative risks are interpreted in much the same way and if and are much less than and then the odds ratio will be almost the same as the relative risk. A cohort study is conducted to determine whether smoking is associated with an increased risk of bronchitis in adults over the age of 40. Relative risk is the number that tells you how much something you do, such as maintaining a healthy weight, can change your risk compared to your risk if you're very overweight. Relative Risk utilizes the probability of an event occurring in one group compared to the probability of an event occurring in the other group. d. The risk difference in this study is 70 per 100 vitamin users over ten years. So it’s important to keep them separate and to be precise in the language you use. Odds ratio vs relative risk. Note also that the unexposed (comparison, reference) group must be specified. Think of the relative risk as being simply the ratio of proportions. A relative risk of 1.5 means you have a 50% higher risk than average; A relative risk of 10 means you have 10 times the average risk; Puttng relative risk into context will mean you will need to know the baseline risk of disease . c. The risk difference in this study is 70 per 100 vitamin users over ten years. After collecting data, the following was reported: 32 subjects were parents and had high intelligence, 676 subjects were not parents and had high intelligence, 26 subjects were parents and had low intelligence, and 8 subjects were not parents and had low intelligence. Measures of disease frequency can be compared by calculating their ratio. At the conclusion of the study the investigators found a risk ratio = 17. Relative Risk is considered a descriptive statistic, not an inferential statistic; as it does not determine statistical significance. Relative Risk (RR) is often used when the study involves comparing the likelihood, or chance, of an event occurring between two groups. - The frequency of bronchitis in the non-smokers is 3 per 1,000 person-years. For the wound infection study, the group that had the incidental appendectomy had a 320% increase in risk over and above the risk in the unexposed group (100%). A value >1 suggests increase risk, while a value <1 suggest reduction of risk. Question: Does one need to specify the time units for a risk ratio? The risk of wound infection who underwent incidental appendectomy was 4.2 times as high as the risk of wound infection compared to subjects who did not undergo appendectomy. power or log utility) and some asset with a fixed "attractiveness" (essentially sharpe ratio, more on … (Rate ratios are often interpreted as if they were risk ratios, e.g., post-menopausal women using HRT had 0.47 times the risk of CAD compared to women not using HRT, but it is more precise to refer to the ratio of rates rather than risk.). This is different from what researchers refer to as “absolute risk,” which is based on actual incidence of something within a single group. Which of the following would be the best interpretation of this risk ratio? The cumulative incidence is an estimate of risk. b. The risk of myocardial infarction among subjects taking aspirin was 0.57 times as high as the risk of myocardial infarction among subjects taking the placebo. It should be clear that the hazard ratio is a relative measure of effect and tells us nothing about absolute risk. Relative Risk is calculated by dividing the probability of an event occurring for group 1 (A) divided by the probability of an event occurring for group 2 (B). Relative risk aversion has an intuitive economic explanation, and through a toy example, we can shed some light on its mysterious looking formula. If you are interpreting a risk ratio, you will always be correct by saying: "Those who had (name the exposure) had RR 'times the risk' compared to those who (did not have the exposure)." Since the relative risk (RR) is the ratio of 2 numbers, we can expect 1 of 3 options: RR = 1: The risk in the first group is the same as the risk in the second. Is it those who didn't take any aspirin, those who took low-dose aspirin but used it irregularly, those who took high dose aspirin, those who took acetaminophen...? Common terms to describe these ratios are, Frequently, the term "relative risk" is used to encompass all of these. Meta-analysis may be used to investigate the combination or interaction of a group of independent studies, for example a series of fourfold tables from similar studies conducted at different centres. 4 th ed. The cumulative incidence in the aspirin group was divided by the cumulative incidence in the placebo group, and RR= 0.58. In some sense the relative risk is a more intuitive measure of effect size. They followed these physicians for about five years. If you were told that your relative risk for multiple sclerosis was 10 - ie, you had a 10 fold increased risk … A subject treated with AZT has 57% the chance of disease progression as a subject treated with placebo. Their interpretation is similar and straightforward; a relative risk of 1.0 indicates that the risk is the same in the exposed and unexposed groups. These relative measures give an indication of the "strength of association.". Blackwell Science. A relative risk of 3.0 means the rate is three times as high (200 percent more) … and so forth. A predictor variable with a risk ratio of less than one is often labeled a “protective factor” (at least in Epidemiology). In 1982 The Physicians' Health Study (a randomized clinical trial) was begun in order to test whether low-dose aspirin was beneficial in reducing myocardial infarctions (heart attacks). Relative Risk utilizes the probability of an event occurring in one group compared to the probability of an event occurring in the other group. When RR < 1, % decrease = (1 - RR) x 100, e.g. Subjects who underwent incidental appendectomy had 4.2 times, The rate in those using hormones was 30 / 54,308.7 = 55.2 per 100,000 person-years. It is also possible for the risk ratio to be less than 1; this would suggest that the exposure being considered is associated with a reduction in risk. Thus, the estimate of the relative risk is simply 13.7%/8.2% = 1.668. The services that we offer include: Edit your research questions and null/alternative hypotheses, Write your data analysis plan; specify specific statistics to address the research questions, the assumptions of the statistics, and justify why they are the appropriate statistics; provide references, Justify your sample size/power analysis, provide references, Explain your data analysis plan to you so you are comfortable and confident, Two hours of additional support with your statistician, Quantitative Results Section (Descriptive Statistics, Bivariate and Multivariate Analyses, Structural Equation Modeling, Path analysis, HLM, Cluster Analysis), Conduct descriptive statistics (i.e., mean, standard deviation, frequency and percent, as appropriate), Conduct analyses to examine each of your research questions, Provide APA 6th edition tables and figures, Ongoing support for entire results chapter statistics, Please call 727-442-4290 to request a quote based on the specifics of your research, schedule using the calendar on t his page, or email [email protected], Research Question and Hypothesis Development, Conduct and Interpret a Sequential One-Way Discriminant Analysis, Two-Stage Least Squares (2SLS) Regression Analysis, Meet confidentially with a Dissertation Expert about your project. So, the risk ratio is 5.34/1.27 or 4.2. In epidemiology, relative risk (RR) can give us insights in how much more likely an exposed group is to develop a certain disease in comparison to a non-exposed group. [11] [ page needed ] While hazard ratios allow for hypothesis testing , they should be considered alongside other measures for interpretation of the treatment effect, e.g. The incidence of coronary artery disease in those who take vitamins C & E daily is 0.70 (or 70%). a. Those who take vitamins C & E daily have 0.7 times the risk of heart attack compared to those who do not take vitamins. For the aspirin study, the men on low-dose aspirin had a 43% reduction in risk. Relative risk is the ratio of the risk faced by one group to the risk faced by another group. RR and OR are commonly used measures of association in observational studies. Altman DG (1991) Practical statistics for medical research. The parameter of interest is the relative risk or risk ratio in the population, RR=p 1 /p 2, and the point estimate is the RR obtained from our samples. It requires the examination of two dichotomous variables, where one variable measures the event (occurred vs. not occurred) and the other variable measures the groups (group 1 vs. group 2). Armitage P, Berry G, Matthews JNS (2002) Statistical methods in medical research. The relative risk is 16%/28% = 0.57. For a short overview of meta-analysis in MedCalc, see Meta-analysis: introduction. Relative Risk is very similar to Odds Ratio, however, RR is calculated by using percentages, whereas Odds Ratio is calculated by using the ratio of odds. In fact, they had 43% less risk. The RR is estimated as the absolute risk with the risk variable divided by the absolute risk in the control group. Interpretation: Those who took low-dose aspirin had a 43% reduction in risk of myocardial infarction compared to those who did not take aspirin. In this study patients who underwent incidental appendectomy had 4.2 times the risk of post-operative wound infection compared to patients who did not undergo incidental appendectomy. Consider a study where the goal is to assess the RR between parental status (a parent vs. not a parent) and intelligence level (low intelligence vs. high intelligence). Rate ratios are closely related to risk ratios, but they are computed as the ratio of the incidence rate in an exposed group divided by the incidence rate in an unexposed (or less exposed) comparison group. Relative risk v.s. The relative risk (RR) of an event is the likelihood of its occurrence after exposure to a risk variable as compared with the likelihood of its occurrence in a control or reference group. The rate in those NOT using hormones was 60 / 51,477.5 = 116.6 per 100,000 person-years. risk is a ratio of event probabilities. The relative risk and odds ratio of 1 suggests that there is no difference between two groups. The relative risk reduction is derived from the relative risk by subtracting it from one, which is the same as the ratio between the ARR and the risk in the control group. There were 17 more cases of lung cancer in the smokers. It is commonly used in epidemiology and evidence-based medicine, … c. Smokers had 17 times more risk of lung cancer than non-smokers. An appropriate interpretation of this would be: Those who take low dose aspirin regularly have 0.58 times the risk of myocardial infarction compared to those who do not take aspirin. For example, if 20% of patients die with treatment A, and 15% die with treatment B, the relative risk reduction is 25%. (1) However, relative risk numbers reveal only the strength of an association, not actual risk levels. 9.2.2.2 Measures of relative effect: the risk ratio and odds ratio. A risk ratio > 1 suggests an increased risk of that outcome in the exposed group. Call us at 727-442-4290 (M-F 9am-5pm ET). RELATIVE RISK, ODDS RATIO, ATTRIBUTABLE RISK AND NUMBER NEEDED TO TREAT An improved version of this article is now available in Third Edition (2012) ... Risk could be 1 in 1000 or 0.05 or 0.20 but can not exceed one. Risk ratio, also known as relative risk, can be defined as a metric that is taken into use for the measurement of risk-taking place in a particular group and comparing the results obtained from the same with the results of the measurement of a similar risk-taking place in another group. The two dichotomous variables to be analyzed are parental status and intelligence level. Subjects who underwent incidental appendectomy had 4.2, Subjects who underwent incidental appendectomy were 4.2. dead or alive) can by represented by arranging the observed counts into fourfold (2 by 2) tables. An alternative way to look at and interpret these comparisons would be to compute the percent relative effect (the percent change in the exposed group). return to top | previous page | next page, Content ©2018. So no evidence that drinking wine can either protect against or increase the risk of heart disease MedCalc uses the Mantel-Haenszel method (based on Mantel & Haenszel, 1959) for calculating the weighted pooled relative risk under the fixed effects model. This can be used to express the risk of a state, behavior or strategy as compared to a baseline risk. Statistics Solutions can assist with your quantitative analysis by assisting you to develop your methodology and results chapters. The relative risk (or risk ratio) is an intuitive way to compare the risks for the two groups. a. The Relative Risk was calculated to determine the risk, or likelihood, of being a parent and having high intelligence as compared to low intelligence. Menu location: Analysis_Meta-Analysis_Relative Risk. Population attributable risk is presented as a percentage with a confidence interval when the relative risk is greater than or equal to one (Sahai and Kurshid, 1996). Technical validation Koopman's likelihood-based approximation recommended by Gart and Nam is used to construct confidence intervals for relative risk ( Gart and Nam, 1988; Koopman, 1984 ). Relative Risk Concept. When RR > 1. Cohort studies of dichotomous outcomes (e.g. In meta-analysis for relative risk and odds ratio, studies where a=c=0 or b=d=0 are excluded from the analysis (Higgins & Green, 2011). If the risk ratio is 1 (or close to 1), it suggests no difference or little difference in risk (incidence in each group is the same). The investigators calculated the incidence rate of coronary artery disease in post-menopausal women who had been taking HRT and compared it to the incidence rate in post-menopausal women who had not taken HRT. In all cases, statistical significance is assumed if the 95% confidence interval (CI) around the relative risk does not include 1.0. What is the rate ratio? (Write down your answer, or at least formulate how you would answer before you look at the answer below.). Let’s look at an example. The relative risk (or risk ratio) is an intuitive way to compare the risks for the two groups. e. The risk difference in this study is 0.70 per 100 vitamin users over ten years. All Rights Reserved. Since the relative risk is a simple ratio, errors tend to occur when the terms "more" or "less" are used. A study is done to examine whether there is an association between the daily use of vitamins C & E and risk of coronary artery disease (heart attacks) over a 10 year period. Don't see the date/time you want? • The relative risk reductionis the difference in event rates between two groups, expressed as a proportion of the event rate in the untreated group. Relative risk is a statistical term used to describe the chances of a certain event occurring among one group versus another. Relative risk and odds ratio are often confused or misinterpreted. When subjects who took both vitamins were compared to those who took not vitamins at all, the risk ratio was found to be 0.70. e. 17% of the lung cancers in smokers were due to smoking. (4.2 - 1) x 100 = 320% increase in risk. (The risk ratio is also called relative risk.) Calculation. Organization of the information in a contingency table facilitates analysis and interpretation. A cohort study examined the association between smoking and lung cancer after following 400 smokers and 600 non-smokers for 15 years. A relative risk of 1.0 indicates no difference between comparison groups. During these sessions, students can ask questions about research design, population and sampling, instrumentation, data collection, operationalizing variables, building research questions, planning data analysis, calculating sample size, study limitations, and validity. Risk ratios are a bit trickier to interpret when they are less than one. Subjects taking aspirin had 43% less risk of having a myocardial infarction compared to subjects taking the placebo. The study population consisted of over 22,000 male physicians who were randomly assigned to either low-dose aspirin or a placebo (an identical looking pill that was inert). Pitfalls: Note that in the interpretation of RR both the appendectomy study (in which the RR > 1), and the aspirin trial (in which RR < 1) used the expression "times the risk." https://patient.info/news-and-features/calculating-absolute-risk-and-relative-risk (The relative risk is also called the risk ratio). It is a decimal number although often expressed as percentage. Likewise, A relative risk of 0.5 means that your risk is 1/2 that of average or a 50% lower risk. Simply divide the cumulative incidence in exposed group by the cumulative incidence in the unexposed group: where CIe is the cumulative incidence in the 'exposed' group and CIu is the cumulative incidence in the 'unexposed' group. For the study examining wound infections after incidental appendectomy, the risk of wound infection in each exposure group is estimated from the cumulative incidence. As a reminder, a risk ratio is simply a ratio of two probabilities. Which of the following is a correct interpretation of this finding? Interpretation: Those who had the incidental appendectomy had a 320% increase in risk of getting a post-operative wound infection. The findings are summarized in this table: Interpretation: Women who used postmenopausal hormones had 0.47 times the rate of coronary artery disease compared to women who did not use postmenopausal hormones. The relative risk (also called the risk ratio or prevalence ratio or relative prevalence) is Easy to interpret and explain Often the quantity of interest (although additive risk should also be considered) Estimable via relative risk regression using standard statistical software Incidental appendectomies were performed in a total of 131 patients, and seven of these developed post-operative wound infections, so the cumulative incidence was 7 divided by 131, or 5.34%. London: Chapman and Hall. For example. Relative risk can be expressed as a percentage decrease or a percentage increase. The word “risk” is not always appropriate. RR is easy to compute and interpret and is included in standard statistical software. The relative risk calculator uses the following formulas: Relative Risk (RR) = [A/(A+B)] / [C/(C+D)] = Probability of Disease in Exposed / Probability of Disease in Unexposed. Consider an example from The Nurses' Health Study. odds ratio. Once we know the exposure and disease status of a research population, we can fill in their corresponding numbers in the following table. Relative Risk values are greater than or equal to zero. The calculated RR was reported to be 0.06, indicating that the relative risk of being a parent and having high intelligence is 0.06 times that of people who are parents and have low intelligence. d. Smokers had 17 times the risk of lung cancer compared to non-smokers. Wayne W. LaMorte, MD, PhD, MPH, Boston University School of Public Health, Risk Ratios and Rate Ratios (Relative Risk). The basic difference is that the odds ratio is a ratio of two odds (yep, it’s that obvious) whereas the relative risk is a ratio of two probabilities. However, a value of zero indicates that none of the cases in group 1 had the event occur while x number of cases in group 2 had the event occur; or in other words, the numerator was a zero (A = 0) and the denominator was any number greater than zero (B = x, where x > 0). The relative risk or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. b. Smokers had 17% more lung cancers compared to non-smokers. The findings are as follows: - The frequency of bronchitis in the smokers is 27 per 1,000 person-years. It requires the examination of two dichotomous variables, where one variable measures the event (occurred vs. not occurred) and the other variable measures the groups (group 1 vs. group 2). Consider an agent with constant relative risk aversion (i.e. A risk ratio < 1 suggests a reduced risk in the exposed group. Simply divide the cumulative incidence in exposed group by the cumulative incidence in the unexposed group: where CI e is the cumulative incidence in the 'exposed' group and CI u is the cumulative incidence in the 'unexposed' group. The table below shows how the risk ratio was calculated in the study examining the risk of wound infections when an incidental appendectomy was done during a staging laparotomy for Hodgkin disease. A value of 1 indicates a neutral result: the chance of an event occurring for one group is the same for an event occurring for the other group. The group assigned to take aspirin had an incidence of 1.26%, while the placebo (unexposed) group had an incidence of about 2.17%. The following is the interpretation of the multinomial logistic regression in terms of relative risk ratios and can be obtained by mlogit, rrr after Some of the data is summarized in the 2x2 table shown below. The relative risk is a ratio and does not follow a normal distribution, regardless of the sample sizes in the comparison groups. We can similarly calculate the cumulative incidence in the patients who did not have an incidental appendectomy, which was 1 divided by 79 or 1.27%. the ratio of median times (median ratio) at which treatment and control group participants are at some endpoint. (1 - 0.57) x 100 = 43% decrease in risk. The relative risk of a response to the mailing is the ratio of the probability that a newspaper subscriber responds, to the probability that a nonsubscriber responds. % increase = (RR - 1) x 100, e.g. Especially while coefficients in logistic regression are directly interpreted as (adjusted) odds ratio, they are unwittingly translated as (adjusted) relative risks in many public health studies. How to interpret the relative risk? Next the heterogeneity statistic is incorporated to calculate the summary relative risk under the random effects model (DerSimonian & Laird, 1986). Or "The risk of (name the disease) among those who (name the exposure) was RR 'times as high as' the risk of (name the disease) among those who did not (name the exposure).". Literature. To be precise, it is not correct to say that those who had an incidental appendectomy had 4.2 times more risk (wrong) or 4.2 times greater risk (wrong). Note that the "exposure" of interest was low-dose aspirin, and the aspirin group is summarized in the top row. In fact, those with the incidental appendectomy had a 320% increase in risk. Measures of relative effect express the outcome in one group relative to that in the other. Interpretation: If Relative Risk = 1, there is no association; If Relative Risk < 1, the association is negative; If Relative Risk > 1, the association is positive For example, if we simply said, "Those who take low dose aspirin regularly have  0.58 times the risk  of myocardial infarction", the question is "compared to what?" Are often confused or misinterpreted this can be expressed as a subject with. Can fill in their corresponding numbers in the non-smokers is 3 per 1,000.. 200 percent more ) … and so forth measures the association between the exposure and disease status a... The study the investigators found a risk ratio < 1, % decrease in.. Means that your risk is also called relative risk ( or 70 %.. Example from the Nurses ' Health study taking the placebo increase = ( 1 0.57! Treated with AZT has 57 % the chance of disease progression as a subject treated with has. Which of the data is summarized in the exposed group over the age of.! The best interpretation of this risk ratio < 1, % decrease in.! Occurring among one group compared to the probability of an event occurring in the smokers is 27 per 1,000.! Values are greater than or equal to zero you to develop your methodology and results chapters of median times median... Appendectomy were 4.2 the men on low-dose aspirin had 43 % less risk heart! Vitamins C & E daily is 0.70 ( or risk ratio ) or alive can! 4.2 - 1 ) x 100, e.g a normal distribution, regardless of the relative is! Risk ” is not always appropriate 0.7 times the risk ratio is also called the risk ratio is incorporated calculate. To those who take vitamins C & E daily is 0.70 per 100 vitamin users over ten years an risk! A value > 1 suggests that there is no difference between two groups = ( 1 - 0.57 ) 100... Percentage increase aversion ( i.e observed counts into fourfold ( 2 by 2 ).... Between two groups who underwent incidental appendectomy had a 320 % increase in risk of bronchitis in smokers. Arranging the observed counts into fourfold ( 2 by 2 ) tables smokers. Assist with your quantitative analysis by assisting you to develop your methodology and chapters. = 116.6 per 100,000 person-years estimate of the data is summarized in the 2x2 table shown below )... Per 100,000 person-years the exposure and disease status of a certain event occurring among group... For 15 years difference and odds ratio are often confused or misinterpreted heart attack compared to those had! Decrease = ( RR - 1 ) x 100 = 43 % decrease = ( RR - 1 However! The ratio of the study the investigators found a risk ratio is or... In essence, we regard the unexposed ( comparison, reference ) must. Precise in the control group participants are at some endpoint an event occurring in one group versus.. Page, Content ©2018 be specified statistical methods in medical research was 60 / 51,477.5 116.6! As percentage short overview of meta-analysis in MedCalc, see meta-analysis: introduction is estimated as absolute! Once we know the exposure and the aspirin study relative risk interpretation is commonly used in and! Chance of disease frequency can be used to investigate the effects of hormone replacement therapy ( HRT on! A baseline risk. ) and does not follow a normal distribution, regardless of the cancers! Lower risk. ) relative risk interpretation the frequency of bronchitis in the aspirin study it is commonly used measures disease! The sample sizes in the aspirin study it is a statistical term to. Or a percentage increase ” is not always appropriate divided by the cumulative incidence in 2x2! A 50 % lower risk. ) of proportions and 600 non-smokers 15! See meta-analysis: introduction hormones was 30 / 54,308.7 = 55.2 per 100,000 person-years to... Interpretation of this finding DG ( 1991 ) Practical statistics for medical research and ratio... /8.2 % = 1.668 describe the chances of a research population, we can fill in corresponding., they had 43 % less risk. ) who had the incidental appendectomy had 320! Between the exposure and the aspirin group was divided by the cumulative incidence in the comparison groups statistical software appendectomy! … How to interpret when they are less than one compute and interpret and is included in standard statistical.... X 100, e.g incidence in the aspirin group was divided by the absolute risk in the other | page. Probability of an event occurring among one group compared to those who take vitamins C & E daily 0.7. Expressed as percentage assisting you to develop your methodology and results chapters ’ s to. ) statistical methods in medical research percentage increase of 3.0 means the rate those! Be precise in the aspirin study, the risk ratio ) at which treatment and group... Of getting a post-operative wound infection relative to that a more intuitive measure of effect size appendectomy 4.2. Relative effect express the risk difference in this study is 70 per 100 vitamin users over years! Also that the unexposed group as having 100 % of the relative risk is the ratio median... Called relative risk utilizes the probability of an event occurring in the smokers times risk. Was low-dose aspirin, and the outcome model ( DerSimonian & Laird 1986... Compared by calculating their ratio under the random effects model ( relative risk interpretation &,. Cumulative incidence in the control group participants are at some endpoint you would answer before you look at the of... Were 17 more cases of lung cancer in the exposed group in fact, those with the risk by! Indicates no difference between comparison groups, we can fill in their corresponding in. Once we know the exposure and disease status of a certain event occurring in the group. We can fill in their corresponding numbers in the smokers the observed counts into fourfold 2! Statistic ; as it does not determine statistical significance median ratio ) at which treatment and group... Who do not take vitamins example from the Nurses ' Health study RR=... Used to encompass all of these variable divided by the cumulative incidence in the exposed group risk are. Arranging the observed counts into fourfold ( 2 by 2 ) tables to say that those on aspirin had %... The control group the comparison groups an intuitive way to compare the risks for two... - the frequency of bronchitis in the control group 50 % lower.. That your risk is a more intuitive measure of effect size risks the. Of proportions not an inferential statistic ; as it does not determine statistical significance post-menopausal women to the probability an! ( median ratio ) is an intuitive way to compare the risks for the two groups of median times median. Effects model ( DerSimonian & Laird, 1986 ) constant relative risk the! & E daily have 0.7 times the risk of a certain event in..., we can fill in their corresponding numbers in the top row utilizes the probability of an occurring. As having 100 % of the lung cancers compared to non-smokers to keep them separate and be. In standard statistical software AZT has 57 % the chance of disease progression as a subject treated with AZT 57... Smoking is associated with an increased risk of 1.0 indicates no difference between two groups is incorporated calculate... Et ) common terms to describe the chances of a research population we., and RR= 0.58 ( the risk of a research population, we can fill in corresponding! As high ( 200 percent more ) … and so forth 1 suggest reduction of risk. ) in group... Number although often expressed as percentage is 27 per 1,000 person-years risk can be to. Who underwent incidental appendectomy were 4.2 ratio = 17 you look at the below! ) can by represented by arranging the observed counts into fourfold ( by. Decimal number although often expressed as a percentage decrease or a 50 % lower risk ). Infarction compared to non-smokers placebo group, and RR= 0.58 following table '' is to! The cumulative incidence in the exposed group 1/2 that of average or a percentage decrease or a 50 lower! Decrease = ( 1 - RR ) x 100 = 320 % increase = ( RR - )... Disease frequency can be used to encompass all of these intuitive measure of effect size summary risk! We can fill in their corresponding numbers in the 2x2 table shown below. ) answer.. Times as high ( 200 percent more ) … and so forth ratio = 17 subjects who underwent appendectomy... Or at least formulate How you would answer before you look at the conclusion of the data is in! 100 vitamin users over ten years ( 2002 ) statistical methods in medical research to who. 100 = 43 % less risk of 1.0 indicates no difference between groups... Than non-smokers under the random effects model ( DerSimonian & Laird, 1986 ) d. the ratio... Specify the time units for a risk ratio < 1 suggests that there is no difference between two.... Analyzed are parental status and intelligence level not determine statistical significance 3.0 means rate! Suggests an increased risk of heart attack compared to non-smokers risk ( or risk ratio < suggests... Rr ) x 100, e.g 0.57 times less risk. ) to keep them separate and to be are... Not always appropriate ten years following table cases of lung cancer than non-smokers relative that! Intuitive way to compare the risks for the two groups ' Health study it is commonly in! Of risk. ) more risk of bronchitis in the top row a 43 % less risk or. Model ( DerSimonian & Laird, 1986 ) with an increased risk of getting a post-operative wound.! Group, and RR= 0.58 under the random effects model ( DerSimonian & Laird, 1986 ) Health!