Re: how does depression affect parenting?
It's impossible to generalize. I would hate to see someone make an important decision about their life, or judge someone else, based on what could be a very temporary condition. Parenting skills, like any other skills, can be learned and improved upon. The job constantly changes as the child grows, so lifelong learning is a must.
There are millions of people with some type of depression and they are all different. Most can be successfully treated. With most of them you wouldn't even know. There are many forms of depression from very mild situational depression to very severe forms of clinical depression. It's really unfortunate that we all use that single term, when there are really many variations. If you find a study that makes a claim about depression, you need to read carefully to see how they define it.
Depression is just one characteristic of a person. Like any other illness or imperfection, the trick is to find ways to accommodate it. No parent is perfect, so it's helpful for all children to have more than one adult in their lives. Adults who can pick up the slack for one another and provide what the children need. Some kids react better to one type of personality at one time in their lives, but they need something else later.
A bout of depression is a character shaping experience. It gives a person a source of empathy and humility that can make them much more understanding of the feelings of other people. People who have never experienced fear or sadness, will be less able to comfort a child who is feeling that way.
On the other hand, a person caught up in a deep depression might be less expressive and engaging, and might want to be left alone. They might be less warm and less optimistic. To put it in perspective, many parents have times when they are preoccupied with an illness, a job, a hobby or chores, and are therefore less attentive than their children need.