wuyuhaili
以下是medcalc软件中的一部分帮助说明,其中disease prevelance一段不知道是什么意思,请教园中高手指点。谢谢!
Statistics
ROC curves
ROC curve analysis
Description
Select ROC curve analysis to obtain a ROC plot and a complete sensitivity/specificity report. A Receiver Operating Characteristic (ROC) curve is a graph that plots the true positive rate in function of the false positive rate at different cut-off points.
Required input
Variable: identify the variables under study.
Classification variable: select or enter a a dichotomous variable indicating diagnosis (0=negative, 1=positive). If diagnosis is coded differently than using the values 0 and 1, you can use the IF function to transform the codes into 0 and 1 values, e.g. IF(RESULT="pos",1,0). (see How to enter data for ROC curve analysis).
Select: (optionally) a selection criterion in order to include only a selected subgroup of cases (e.g. AGE>21, SEX="Male").
Disease prevalence: if the sample sizes in the positive and the negative group do not reflect the real prevalence of the disease, this must be indicated in the dialog box. You then have the option to enter the disease prevalence. Clinically, the disease prevalence is the same as the probability of disease being present before the test is performed. If the disease prevalence is unknown, or irrelevant for the current statistical analysis, you can ignore the fields concerning this matter and proceed by selecting the OK button. In this case the program will not calculate predictive values. When you select the option Full ROC report, the program will list sensitivity and specificity for all possible threshold values. If this option is not selected, then the program will only list the more important points of the ROC curve: for equal sensitivity/specificity it will give the threshold values (criterion values) with the highest specificity/sensitivity.
hellofun
疾病患病率: 当阴性数和阳性数不能反映真实的疾病患病率时,对话框会有提示。此时你可以选择性输入疾病患病率。临床上,疾病患病率与检测前疾病出现的概率是相等的,如果患病率未知,或患病率与当前的统计分析无关,你也可以忽略该步骤(即不输入患病率),直接按“确定”键到下一步。在这种情况下,程序将不会计算出预测值(即阳性预测值和阴性预测值)。
感觉英文蛮好理解的,翻译成中文倒有点别扭,如果还看不懂,请多包涵。
另外,建议你能对ROC曲线,敏感度,特异度,假阳性率,假阴性率,阳性预测值,阴性预测值等的概念和相关公式有所了解。预测值的计算是必须要有患病率的,如阳性预测值=(敏感度×患病率)/[(敏感度×患病率)+(1-特异度)×(1-患病率)]。
上面那段话的意思也就是说,如果按照选定的阈值,检测人群中阳性的概率跟患病率不相等时,程序会给出提示,让你输入患病率。此时你可以输也可以不输(如果你不知道患病率的话可不输)。如果不输,则程序照样运行,但最后不能给出阳性预测值和阴性预测值。