Ask most clergy, and they will say that congregational numbers aren't really what it's about. Scratch a little under the surface, and you'll probably find that they matter a bit more than they let on. My own view is that numbers aren't everything, but they are something.
When it comes to church membership statistics, the real problem is what figures do you look at? After all, my 8am 1662 communion grew by over 50% last week. 11 people were there, compared with 7 the week before. The facts were that someone was back from holiday, and someone else who normally comes at 10am came... you get the point.
One figure that is often used is the number of people who received communion (communicants in Churchspeak) In our church during Lent, that figure moved around erratically between just over 70 to well over 100 at our main 10am service. What does that tell us? Well, it's a measure of the number of people present who believed they were eligible to receive. It doesn't tell us how many adults or young people were there. On top of that, we have additional people receiving communion at 8am and once a month at 6.30, plus some people come twice. Then there are the people at the midweek service, including some who were there on Sunday and some who weren't. And today I gave 8 people communion at a little service in a nursing home (altogether we can sometimes provide communion for nearly 20 people in a month who don't make it to church). So how many per week communicants do we have? Not straightforward.
Then there's attendance. In October we take the official stats, and they can be helpful to monitor what's going on. Again, we have to filter out 'twicers' and include midweek. Then there's the question of how to monitor children and young people - separately or in with the adults? We also have to take into account fluctuations due to special services - main service baptisms, Harvest Festival, which might distort the attendance we would have had if it wasn't a special. [still with me?] This leads to a statistic called the Usual Sunday Attendance (USA), which was a kind of average of the Sunday adult attendance across all services, eliminating duplicates. Now, the weekly attendance is the more accepted figure, which takes into account those who attend midweek but not on a Sunday.
However, now that Fresh Expressions has led to new expressions of Church, such as Messy Church, Alternative Worship and other congregations starting up, often not on a Sunday, it's not so clear what the 'attendance' is. People at these new expressions of Church don't necessarily regard themselves as committed to the parish church that enabled them to come into being. Perhaps it all goes to show that however hard you try, measuring any kind of human behaviour (including worship) doesn't fit neat boxes or categories.
Even if you have a good sequence of stats, you need to be very discerning about what to read into them. For example, when I was in Coventry, I was 1/2 time priest-in-charge of a modestly sized parish. When I arrived the Usual Sunday Attendance (USA) was 38, by the time I left it was between 46 & 47. That's Ok - it's growth, albeit not very spectacular. However, when I looked carefully, I realised that during those 8 years a number of regular attenders had died, and a few people had moved away, totalling about 22 in all. That means that the 46 we had in 2002 only contained about 16 or 17 of the original congregation. That's nearly 30 new people in 8 years. Still not spectacular, but perhaps more substantial than the initial stats would suggest. Standing still would have been quite good going.
And even then we haven't got to the bottom of things. Nowadays, it's clear that a lot of people attend less frequently than was once the case. So quite a few churches have a growing 'pool' of churchgoers, but fewer in church on any one Sunday. To some extent, that seems to be the case in my present church, where our Electoral Roll (the nearest the C of E comes to a membership list) has grown and is now mainly people who come to church at least sometimes or receive home communion. Meanwhile attendance is fairly static. Is that growth, shrinkage or what?
Perhaps we all need to hold on to the fact that stats can be used to say most things in the hands of a clever statistician. The real job for the leadership of a church isn't spending all our time on attendance graphs, but being faithful in worship and prayer, listening for God's guidance and seeking to have a positive impact on our community.