What does I2 mean in heterogeneity?
The I² statistic describes the percentage of variation across studies that is due to heterogeneity rather than chance (Higgins and Thompson, 2002; Higgins et al., 2003). I² = 100% x (Q-df)/Q. I² is an intuitive and simple expression of the inconsistency of studies’ results.
What does heterogeneity in a meta-analysis mean?
Heterogeneity is not something to be afraid of, it just means that there is variability in your data. So, if one brings together different studies for analysing them or doing a meta-analysis, it is clear that there will be differences found.
What is the I2 index?
The I2 index measures the extent of true heterogeneity, dividing the difference between the result of the Q test and its degrees of freedom (k 1) by the Q value itself and multiplying by 100. So, the I2 index is similar to an intra- class correlation in cluster sampling (Higgins & Thompson, 2002).
What is the difference between homogeneity and heterogeneity?
In most technical applications homogeneous means that the properties of a system are the uniform throughout the entire system; heterogeneous (also inhomogeneous) means that the properties change within the system. Any system with two phases like ice and water are said to be heterogeneous.
Is homogeneity good in meta-analysis?
Meta-analysis seeks to combine the results of several experiments in order to improve the accuracy of decisions. It is common to use a test for homogeneity to determine if the results of the several experiments are sufficiently similar to warrant their combination into an overall result.
Is high heterogeneity bad in meta-analysis?
In extreme cases, very high heterogeneity can mean that the studies have nothing in common, and that it makes no sense to interpret the pooled effect at all. Therefore, meta-analysts must always take into account the variation in the analyzed studies.
What does the I2 statistic mean?
of heterogeneity
The I2 statistic is a test of heterogeneity. I2 can be calculated from Cochran’s Q (the most commonly used heterogeneity statistic) according to the formula: I2 = 100% X (Cochran’s Q – degrees of freedom). Any negative values of I2 are considered equal to 0, so that the range of I2 values is between 0-100%.
What does P value for heterogeneity mean?
To determine whether significant heterogeneity exists, look for the P value for the χ2 test of heterogeneity. A high P value is good news because it suggests that the heterogeneity is insignificant and that one can go ahead and summarise the results.
Is I2 an absolute measure of heterogeneity?
Basics of meta-analysis: I 2 is not an absolute measure of heterogeneity When we speak about heterogeneity in a meta-analysis, our intent is usually to understand the substantive implications of the heterogeneity.
How do you interpret heterogeneity in a meta-analysis?
When we speak about heterogeneity in a meta-analysis, our intent is usually to understand the substantive implications of the heterogeneity. If an intervention yields a mean effect size of 50 points, we want to know if the effect size in different populations varies from 40 to 60, or from 10 to 90, …
What is the bias of I2 in meta-analysis?
In meta-analysis, the fraction of variance that is due to heterogeneity is estimated by the statistic I2. We calculate the bias of I2, focusing on the situation where the number of studies in the meta-analysis is small.
What is considered significant heterogeneity in research?
In general, significant heterogeneity is considered to be present if I 2 is 50% or more. In the above meta-analysis, I 2 was reported as 55.6%, indicating the presence of significant heterogeneity (c is false) and confirming the result of Cochran’s Q test.