several early studies demonstrated improved survival for patients treated with thrice weekly haemodialysis at home [ 4 , 5 ] . this review is limited to more recent studies ( table 1 ) , after home haemodialysis prevalence had started to decline in most countries . home haemodialysis survival studies hd , haemodialysis ; pd , peritoneal dialysis ; dd , deceased donor ; ld , live donor ; rr , risk ratio . in a single - centre us study , patients survived longer on home than hospital haemodialysis or peritoneal dialysis [ 68 ] , but were younger , had fewer co - morbidities and were less likely to have higher risk renal diseases . the survival advantage persisted after multivariate adjustment using a cox regression . in a retrospective study from two centres in the west of scotland , home haemodialysis patients were compared to age- and sex - matched peritoneal dialysis patients , with diabetics excluded . co - morbidity analysis was limited , but there were fewer smokers and fewer electrocardiograph abnormalities in the home haemodialysis patients . a single - centre swiss study compared home to in - centre haemodialysis . controls were matched for age , sex , primary renal disease and dialysis vintage . despite the low proportion of patients treated with home haemodialysis , controls could not be found for 44% . even after matching , home haemodialysis patients still had fewer co - morbidities ( not statistically significant ) . meier analysis showed a substantial survival advantage for home patients and significantly fewer hospital admissions . covariates were assessed in a cox model ( age , gender , renal disease co - morbidity , smoking status , marital status and year of starting dialysis ) and the survival advantage persisted . both groups of patients were only dialysed 2.32.5 times per week for 9.49.5 h per week , limiting generalizability in the modern era . using the case mix severity study ( a nearly random sample of us dialysis patients ) , home haemodialysis patients were compared to in - centre patients using cox regression . there were difficulties defining whether patients were on home haemodialysis , because of patients receiving assisted home haemodialysis , and self - care haemodialysis patients in - centre , but a stringent definition was used , which required patients to be receiving home haemodialysis training on day 30 after starting dialysis . home haemodialysis patients were younger and less likely to have diabetic nephropathy , congestive heart failure , myocardial infarctions , strokes or obesity . after multivariate analysis ( including age , gender , race , diabetic nephropathy and co - morbidity ) , a substantial survival advantage persisted for home haemodialysis . a confirmatory analysis using all patients in the united states renal data system ( usrds ) database also showed a survival advantage , though less impressive , and not adjusted for co - morbidity . it should be noted that hospital haemodialysis in the usa had generally poor outcomes at this time making it difficult to interpret these results . in a recent registry analysis from england and wales , home haemodialysis patients were compared to age- and sex - matched controls treated with hospital haemodialysis , satellite haemodialysis or peritoneal dialysis . home haemodialysis patients were more likely to be white , less likely to be socially deprived and had lower risk renal diseases . this study did not assess co - morbidity other than renal disease , but used wait - listing for transplantation as a surrogate marker of global health status . cox models ( incorporating age , gender , renal disease , ethnicity , social deprivation , wait - listing for transplant and time - dependent variables for home haemodialysis and transplantation ) showed a significant survival advantage of home haemodialysis compared to peritoneal dialysis . an advantage of similar magnitude was seen compared to hospital haemodialysis but did not achieve significance . there was no difference compared to satellite haemodialysis , but that analysis was limited by lack of power . interestingly , patients did not start home dialysis for a median of 12 months after starting renal replacement therapy , so none of these patients would have been included in the us study . it is clear from these studies that the survival benefit of home haemodialysis is explained at least partly by patient selection ; but despite varied statistical approaches , all show residual unexplained survival advantage after adjustment . while this could be due to confounding by unmeasured factors , are there other possibilities ? anecdotally , patients dialysing at home sometimes perform additional sessions . while not equivalent to frequent haemodialysis , these sessions may be performed at crucial times such as when fluid overloaded or after a potassium - rich meal . secondly , patients whose psychological preference is to control their environment may have reduced stress and better outcomes when the treatment approach is congruent with their psychological preferences [ 14 , 15 ] . conversely , patients who prefer to give others control might not benefit from home haemodialysis . more recently , studies have examined patient outcomes on short - daily haemodialysis ( sdhd ) and nocturnal haemodialysis ( nhd ) , mostly performed at home . in a small us study , mortality of 117 patients on sdhd ( 16% in - centre ) followed for up to 2 years was substantially lower when compared to the usrds population using the standardized mortality ratio ( smr ) , adjusting for age , sex , race and renal disease . in a european population of 415 sdhd patients ( 36% in - centre ) , survival was substantially better than the usrds population , again using the smr approach . perhaps more impressively , the home sdhd patients had equivalent survival to deceased donor kidney transplant recipients . the toronto group compared survival of 177 nhd patients to 531 deceased donor and 531 live donor kidney transplant recipients from the usrds , matched for race , diabetes and prior treatment duration with conventional haemodialysis . cox regression showed no difference in survival between nhd and deceased donor transplant patients , although live donor transplants had superior survival . a recent five - centre us study compared outcomes in 94 nhd and 43 sdhd home patients to the usrds population using propensity score matching . survival was significantly better after cox regression for nhd but was not significant for sdhd . the conventional haemodialysis control group were somewhat unusual in that they dialysed for only 3 h per session ( compared to 2.9 h for sdhd ) , but for 3.5 times per week , and this may have confounded the results , particularly for the sdhd group . in these studies , mortality improvement is impressive , with a 3666% reduction compared to a 2251% improvement with conventional home haemodialysis . two studies have in part addressed the issue of patient selection by showing comparable survival to deceased donor kidney transplant recipients , a group which should be at least as selected . it remains unclear how much of the improved survival in these studies is due to frequent dialysis and how much to dialysis at home . the frequent dialysis network trials should cast some light on this issue   by comparing sdhd to conventional haemodialysis in - centre and nhd to conventional haemodialysis at home ; but these studies are only powered to compare composite end points incorporating mortality , left ventricular mass and quality of life . the sdhd study showed significant improvement in both composites with hazard ratios of 0.61 and 0.70 respectively . mortality at one year was 4% in the sdhd arm ( n = 125 ) and 7.5% in the control arm ( n = 120 ) . if one accepts that a randomized trial of home haemodialysis with power to assess mortality is unlikely to be performed , then what can further observational research add ? a large , multinational retrospective observational study of outcomes may still be of value as numbers remain relatively small in the studies above . nevertheless , despite multivariate analysis a retrospective study the freedom study is a prospective observational study of sdhd using the nxstage machine   and has started to report benefits including reduced depression , improved sleep quality and reduced recovery time after dialysis . establishing a similar , detailed , large prospective observational study of the various types of home haemodialysis may address some of the problems of confounding ( e.g. co - morbidity ) more convincingly . mortality is attractive as a definitive binary outcome , but other outcomes are also important to patients lives . end points such as blood pressure , left ventricular mass [ 20 , 23 ] or serum phosphate   can be used but are in essence surrogates for mortality . the early literature addressed impact on quality of life and psychosocial functioning but to a limited extent , and there is scope for more detailed research . lindsay   published a seminal study asking patients the simple question ,  how long does it take you to recover from a dialysis session? and demonstrated dramatic differences between conventional haemodialysis ( 7 h 5 min ) , sdhd ( 34 min ) and nhd ( 9 min ) . one could combine such data with the lean management approach   of defining activity as value - added or non - value - added from the patient s perspective ( table 2 ) . this could lead to innovative end points , which may capture the impact of dialysis on patients lives in a more rounded fashion . at the very least comparison of impact of different haemodialysis modalities , using a lean approach of value to patient value - added time is the remaining waking time , and non - value added time is the total treatment time , both expressed as a percentage of total waking hours . chd , conventional haemodialysis ( thrice weekly for 4.5 h per session ) ; chhd , conventional home haemodialysis ; sdhd at home ( six times weekly for 2.25 h per session ) ; nhd ( six times weekly for 6 h per session ) . data from macgregor and allan . observational data have consistently shown improved mortality with home haemodialysis , and frequent dialysis seems to add an even greater benefit approaching that of deceased donor kidney transplantation . however , these retrospective observational studies are likely to overestimate benefit . as randomized trials seem unlikely , consideration should also be given to assessing a range of end points in addition to mortality , with a particular focus on those that represent the overall impact of dialysis on patients lives .
health care policy is encouraging expansion of home haemodialysis , aiming to improve patient outcomes and reduce cost . 
 however , most patient outcome data derive from retrospective observational studies , with all their inherent weaknesses . 
 conventional thrice weekly home haemodialysis delivers a 2251% reduction in mortality , but why should that be ? 
 frequent and/or nocturnal haemodialysis reduces mortality by 3666% , with comparable outcomes to deceased donor kidney transplantation . 
 approaches which might improve the quality of future observational studies are discussed . 
 patient - relevant outcomes other than mortality are also discussed .