Table 2.

Properties and characteristics of meta-analyses of the neuropsychological effects of DBS

Reference	Number of Studies Included	Sample Size	Comments	Cognitive Domain (D) or Test (T) Effect Sizes/Mean Standardized Differences (MSD) Provided	Fixed or Random Effects Model(s)	STN SMD	GPi SMD	STN versus GPi Direct Comparison SMD	Unilateral versus Bilateral Comparison SMD
Parsons et al. (2006)	28	612		D	Random	Yes	No	No	No
Combs et al. (2015)	38	1622	Includes mix of unilateral and bilateral DBS	D	Random	Yes	Yes	No	No
Wang et al. (2016)	7	521	Includes RCTs only; 7 studies from 4 trials; mix of unilateral and bilateral	D	Both depending on heterogeneity	No	No	Yes	No
Xie et al. (2016)	10	797	RCTs and non-randomized, controlled trials only	T	Both depending on heterogeneity	Yes	No	No	No
Elgebaly et al. (2017)	4	345	4 RCT in meta-analysis, 7studies for qualitative analysis	T	Both depending on heterogeneity	No	No	Yes	Yes (subgroup analysis)
Martínez-Martínez et al. (2017)	50	Total not given; 69–246 per test	Executive function tests only; includes 1 GPi study	T	Both depending on heterogeneity	Yes (but includes 1 GPi)	No	No	No

Note: GPi = globus pallidus internus; RCT = randomized controlled trial; SMD = standardized mean difference (effect size); STN = subthalamic nucleus.