I'm procrastinating revising for my Paper 2 psychology exam so here you go, I hope this helps. <3
Currently, the opening sentence isn't relevant enough to the question to get you a mark. Why does it allow psychologists to investigate cultural variations? Because the SS experiment uses lots of standardisation with ordered steps that make it easy for psychologists across the world to replicate it exactly the way the original study did it. So either explain why by saying the above or you can remove the sentence and get right into the juicy details of Van Izjendoorn because that's where most of the marks are.
Van Izjendoorn did not conduct a study, each experiment conducted was a study of its own, he just read all of the reports of the 32 studies and analysed them and you correctly identified this as being called a meta-analysis.
I'm nitpicking here because for the rest of the essay you refer to the research correctly but I'm using it more as an example of how minor inaccuracies affect the examiner's decision on what level of response your essay is.
Level 4 (13-16 marks) = Knowledge is accurate and generally well detailed.
Level 3 (9-12 marks) = Knowledge is evident but there are occasional inaccuracies/omissions.
I wouldn't say this is right. The more accurate interpretation of why Japan and Israel had higher rate of insecure-resistant is because they have a more collectivist culture (1 mark) which emphasises selflessness and a dependence on family (1 mark). While Germany and UK have a higher rate of avoidant because of individualistic culture which emphasises independence and being self-sufficient which you slightly leaned into explaining when you said "German parents seek independent, non-clingy infants." but you can further develop that by linking it to the specialist terminology "individualistic culture".
I'm gonna return to how a Level 3 response is described: Knowledge is evident but there are occasional inaccuracies/omissions.
Omission means things being left out. You have left out quite an important section of Van Izjerndoorn which is intercultural and intracultural variations. He found that intracultural variations which are differences within a culture (1 mark) were larger than intercultural variations, differences between cultures. This significant part of the meta-analysis findings make your final evaluation point void.
Izjerndoorn addresses this possibility with his intracultural findings because the fact that differences within one culture were larger than the difference between cultures suggested to him that there are other factors like socioeconomic background which also affect attachment type and this was included in his report.
Now that you know that US, UK, Germany are individualistic cultures, you can develop this evaluation point further. The results aren't distorted because it's uneven from each country, they're distorted because it's uneven from each culture e.g. individualistic and collectivist. There were more studies done in countries with individualistic cultures so the data is culturally biased (1 evaluation) so the meta-analysis results aren't generalisable to the entire population, which lacks population validity (another evaluation). Be specific in what kind of validity. Saying this affects the validity of the study is very vague, you haven't even specified if it affects validity positively or negatively, and you get marks for that. You get a mark for saying this is a weakness, so always make sure you finish (or start like you did for the first) evaluation point by saying this is a strength or this is a weakness.
I would give this 10/16 marks. You either need to expand your evaluation points or you need to do more of them but in less detail (and obviously ensure that they are correct, for example I don't think your last eval point would get more than one mark)
I would generally recommend you to memorise an essay plan so you have condensed all your knowledge into 10ish bullet points and try not to waste any sentences on something that isn't a bullet point. Also, memorising 16 marker essay plans is a great revision tool because if you are able to remember a guaranteed full mark essay plan for the highest mark question, then you're obviously guaranteed to know the information to get full marks on the 1 markers and 4 markers and 8 markers.