| Study | Reason for exclusion |
|---|---|
| Adamson 2010 | Unclear whether children with Down syndrome were included, compared 3 types of parent‐mediated intervention, and outcomes were only measured in terms of joint attention and not language or communication |
| Allen 1980 | Not an RCT and did not measure language or communication skills |
| Allin 1988 | Targeted problematic behaviour and not language or communication |
| Aparicio 2003 | Parent‐mediated intervention in both arms of the trial |
| Bagner 2007 | Targeted problematic behaviour and not language or communication |
| Bagner 2016 | Did not include children with Down syndrome |
| Baker 1980 | Parent‐mediated intervention in both arms of the trial and did not target language or communication |
| Baker 1984 | Parent‐mediated intervention in both arms of the trial and did not target language or communication |
| Barna 1980 | Not an RCT |
| Barnett 1988 | Did not include children with Down syndrome |
| Bauer 2014 | Not an RCT |
| Bauer 2015 | Not an RCT |
| Baxendale 2003 | Did not include children with Down syndrome |
| Bennett 1983 | Not an RCT, did not include children with Down syndrome, and did not measure language or communication |
| Bidder 1975 | Not an RCT |
| Boyce 1993 | Results for children with Down syndrome were not reported separately, and study authors did not reply to our attempts to contact them |
| Buschmann 2010 | Not an intervention study |
| Campbell 1978 | Not an RCT, unclear whether children with Down syndrome were included, parent‐mediated intervention in both arms of the trial |
| Cologon 2017 | Parent‐mediated intervention in both arms of the trial |
| Coutinho 2003 | Targeted family functioning and use of support networks and not language or communication |
| Del Giudice 2006 | The intervention was behavioural in its approach and did not provide results for language and communication separately |
| Estes 1984 | Not an intervention study |
| Gibbard 1992 | Did not include children with Down syndrome |
| Gibbard 1994 | Did not include children with Down syndrome |
| Gibbard 2004 | Not an RCT and did not include children with Down syndrome |
| Girolametto 1988 | Results for children with Down syndrome were not reported separately |
| Haney 1993 | Did not include children with Down syndrome |
| Hassiotis 2017 | Did not measure speech, language or communication |
| Heifetz 1977 | The intervention targeted self‐help and not language or communication |
| Hopman 1989 | Not an intervention study |
| Hornby 1984 | Children were not aged 0‐6 years |
| Hudson 1982 | Results for children with Down syndrome were not reported separately, intervention was behavioural, and did not measure language or communication |
| Hwang 2013 | Included only one child with Down syndrome and parent‐mediated interventions in both arms of the trial |
| Innocenti 1993 | Results for children with Down syndrome were not reported separately, and study authors did not reply to our attempts to contact them |
| Karaaslan 2013b | Results for children with Down syndrome were not reported separately and study authors did not reply to our attempts to contact them |
| Kashima 1988 | The intervention targeted self‐help skills and not language or communication |
| Leung 2016 | Did not include children with Down syndrome |
| Mahoney 1985b | Did not include children with Down syndrome |
| Mahoney 1998 | Not an intervention study or RTC and parent mediated intervention in both arms of the trial |
| McIntyre 2008 | Did not include children with Down syndrome, and the intervention targeted problematic behaviour and not language or communication |
| McNally 2008 | Not an intervention study |
| Moxley‐Haegert 1983 | Did not include children with Down syndrome |
| NCT02158390 | Parent‐mediated intervention in both arms of the trial |
| Niccols 2000 | Not an RCT, and the intervention did not target language or communication |
| Pelchat 1999 | Not an RCT |
| Pratt 2015 | Did not include children with Down syndrome |
| Roberts 2006 | Targeted problematic behaviour and not language or communication |
| Roberts 2015 | Did not include children with Down syndrome |
| Roux 2013 | Targeted problematic behaviour and not language or communication |
| Russell 2004 | Parent‐mediated intervention in both arms of the trial |
| Schoenbrodt 2016 | Not an RCT and did not include children with Down syndrome |
| Seifer 1991 | Parent‐mediated intervention in both arms of the trial |
| Shapiro 2014 | Targeted problematic behaviour and not language or communication |
| Sofronoff 2011 | Targeted problematic behaviour and not language or communication |
| Tannock 1992 | Results for children with Down syndrome were not reported separately as the data had been destroyed |
| Te Kaat‐van den Os 2017 | Not an RCT but a systematic review |
| Warren 2008 | The intervention had parent‐mediated intervention in both arms of the trial |
| Woynaroski 2014 | Parent‐mediated interventions in both arms of the trial |
| Wright 2017 | Not an RCT |
RCT: randomised controlled trial.