BPC

The way I see it, there are a few different components that make up "research experience" as a whole. 1. The amount of time you actually spent. This can be judged very generally. 6 months is very little, 5 years is a lot. A person could, in theory, make this up. In my opinion - just giving the amount of time you spent in a lab is not a very good indicator of anything. It probably matters less for admissions. 2. The letter of recommendation you get out of it. This is HUGE. It is arguably the most important component of your application. It assigns some sort of value to all of that time you spent. Some things to keep in mind: The stronger your relationship with this person - the better. The more you impressed them - the better. The more people that can speak on your research abilities - the better. So rather than judging how a few extra hours a week is going to look to an adcom, you should be thinking about how strong a relationship you can foster with that professor and how good the LOR will be. Again, time is not going to be judged as much as the letter. 3. Gaining actual research experience: Being able to speak well about your research, applying what you've learned about, and asking the right questions as well as designing the right experiments. This will most likely show through in your SOP and interviews. Obviously, you're going to be much more knowledgeable for every additional year you spend doing research. However, across individuals, some are going to develop this quicker than others. You need to sort of judge yourself on this. Again - this plays into your SOP. Your SOP and LORs are the two most important parts of your application. They are both affected by the amount of research experience you have, but aren't necessarily going to be of some value Y after timeframe X. I realize this entire response has just been a lot of fluff and I haven't really given advice, so here it is: I think you should do the extra lab work because it will expand your horizons, most likely leading to a more informed SOP and hopefully a good LOR from that PI as well. And on a side note, the exact topic of your research won't make as much of a difference. My most notable research experiences were in a field outside of what I'm going to be doing in graduate school. Look at it as a chance to display your research potential in general.

I would have a completely different take on "Why have you chosen us?". The school knows they are good. The profs and adcoms don't need to be reminded that you want to go there. You have everything to gain by going there - so why do THEY want YOU? So essentially - I would talk about what is so great about you and what about the school fits well with your strengths. Telling them that they have strong faculty and a good library doesn't give them a reason to accept you. Sell yourself more.

I had a similar issue - a very clear divide in my transcript between below 3.0 semesters and straight 4.0's in the second half (with an alright cum. GPA). I also didn't have a good reason besides being unmotivated and in a slightly different major. I originally wrote a paragraph explaining this, but I cut it to a sentence because there was just too much more to talk about. My advice is don't even say anything negative about your first two years. Find a good place where it will "flow" and put a sentence in with a positive statement about your second half and be done with it. Draw attention to the fact that you excelled towards the end, not to the fact that you did poorly in the beginning - if that makes sense.

I don't think it will work against you at all. Graduate schools keep track of their matriculation rates, and they prefer that more students that they admit end up accepting offers. Consequently, a school is much more likely to accept you if they know that you will accept the offer (since it helps boost their stats). You don't have to explain the situation. Just tell them that Caltech is your top choice program and that you're wondering if they are still considering you for admission. There is no reason to play "hard to get" during the application process. At the same time, it is unnecessary to tell them that you don't have any offers yet.