So I want to talk to you today about AIDS in sub-Saharan Africa. And this is a pretty well-educated audience, so I imagine you all know something about AIDS. You probably know that roughly 25 million people in Africa are infected with the virus, that AIDS is a disease of poverty, and that if we can bring Africa out of poverty, we would decrease AIDS as well. If you know something more, you probably know that Uganda, to date, is the only country in sub-Saharan Africa that has had success in combating the epidemic. Using a campaign that encouraged people to abstain, be faithful, and use condoms -- the ABC campaign -- they decreased their prevalence in the 1990s from about 15 percent to 6 percent over just a few years. If you follow policy, you probably know that a few years ago the president pledged 15 billion dollars to fight the epidemic over five years, and a lot of that money is going to go to programs that try to replicate Uganda and use behavior change to encourage people and decrease the epidemic.
我今天要講的是撒哈拉以南非洲的愛滋病情形 各位教育程度都很高 所以大家應該都知道愛滋病 在非洲有2500萬人 感染愛滋病病毒,而且它也是窮人的疾病 如果能幫助非洲脫離貧窮,那愛滋病也會減少 還有,烏干達現在是撒哈拉以南非洲地區 唯一成功對抗這流行病 的國家 他們宣導ABC運動:戒絕、忠貞、保險套 成功在1990年,減低愛滋傳播率 幾年間,從15%降到6% 如果你關心政策,你應該知道幾年前 總統投入15億美元,對抗愛滋病 大部分的資金,都投入類似烏干達的計畫 利用行為改變,來鼓勵人們,以減低傳染
So today I'm going to talk about some things that you might not know about the epidemic, and I'm actually also going to challenge some of these things that you think that you do know. To do that I'm going to talk about my research as an economist on the epidemic. And I'm not really going to talk much about the economy. I'm not going to tell you about exports and prices. But I'm going to use tools and ideas that are familiar to economists to think about a problem that's more traditionally part of public health and epidemiology. And I think in that sense, this fits really nicely with this lateral thinking idea. Here I'm really using the tools of one academic discipline to think about problems of another.
所以我今天要談一些 關於愛滋,你們所不知道的事 再來我要挑戰一些 你們已知的事 我先談我身為經濟學家 對於愛滋病所做的研究 我不會談太多經濟的東西 也不會講進出口價格 但我要用一些經濟學家常用的方法 來解釋流行病學、公共衛生 衍生出的問題 這樣很符合橫向思維的概念 運用一種學術領域的工具 來解決其他領域的問題
So we think, first and foremost, AIDS is a policy issue. And probably for most people in this room, that's how you think about it. But this talk is going to be about understanding facts about the epidemic. It's going to be about thinking about how it evolves, and how people respond to it. I think it may seem like I'm ignoring the policy stuff, which is really the most important, but I'm hoping that at the end of this talk you will conclude that we actually cannot develop effective policy unless we really understand how the epidemic works.
首先,愛滋病跟政策有關 可能在座大部分的人,也是這麼認為 但我要講的是,關於理解疫情傳播的事實 關於思考它的形成原因,人們的反應 看來我可能會忽略政策之類的東西 雖然政策是最重要的 但演講結束你會明白 除非了解疾病的傳播 我們是無法訂定有效政策的
And the first thing that I want to talk about, the first thing I think we need to understand is: how do people respond to the epidemic? So AIDS is a sexually transmitted infection, and it kills you. So this means that in a place with a lot of AIDS, there's a really significant cost of sex. If you're an uninfected man living in Botswana, where the HIV rate is 30 percent, if you have one more partner this year -- a long-term partner, girlfriend, mistress -- your chance of dying in 10 years increases by three percentage points.
我想講的第一點 我們必須理解的第一點是 人們對於愛滋病的反應是什麼? 愛滋病是性傳播疾病,會致死 所以愛滋病盛行的地方 性行為的代價也高 波紮那的病毒感染率30%,如果你是個健康的男人 你今年多了一個性伴侶-長期的、女友、情婦也好 你十年內死亡率會提高三個百分點
That is a huge effect. And so I think that we really feel like then people should have less sex. And in fact among gay men in the US we did see that kind of change in the 1980s. So if we look in this particularly high-risk sample, they're being asked, "Did you have more than one unprotected sexual partner in the last two months?" Over a period from '84 to '88, that share drops from about 85 percent to 55 percent. It's a huge change in a very short period of time.
這是很驚人的 所以我們會覺得,人們真的要減少性行為 事實上,美國的同性戀中 在1980年代,我們確實看到這種改變 仔細觀察高危險群,當他們被問到: 「過去的兩個月內,你是否有一個以上,未採取保護措施的性伴侶?」 數據顯示,從84到88年,比例從85%下降到55% 這麼短時間內,這是很大的改變
We didn't see anything like that in Africa. So we don't have quite as good data, but you can see here the share of single men having pre-marital sex, or married men having extra-marital sex, and how that changes from the early '90s to late '90s, and late '90s to early 2000s. The epidemic is getting worse. People are learning more things about it. We see almost no change in sexual behavior. These are just tiny decreases -- two percentage points -- not significant.
在非洲我們從未看到這樣的改變 我們沒有足夠的數據,但你可以看到 這是單身男人婚前性行為 或已婚男人的婚外性行為的數據比例 從90年代初期到末期的改變 以及90年末到2000年初期的改變,疫情變嚴重了 人們對疾病的瞭解更多 但性行為上卻幾乎沒有變化 只有降低極少的2%而已
This seems puzzling. But I'm going to argue that you shouldn't be surprised by this, and that to understand this you need to think about health the way than an economist does -- as an investment. So if you're a software engineer and you're trying to think about whether to add some new functionality to your program, it's important to think about how much it costs. It's also important to think about what the benefit is. And one part of that benefit is how much longer you think this program is going to be active. If version 10 is coming out next week, there's no point in adding more functionality into version nine.
看來很怪,但你不應該對此感到吃驚 想要理解原因,你要用經濟學家的思維 來思考健康議題,用投資的概念 如果你是個軟體設計師,當你在想 是否要在你的設計裡,加一些新的功能時 成本是必須考慮的 收益也是必須考慮的 考慮收益的其中一個方法就是 你的軟體離推出還有多久 如果第十版下週推出 那就沒必要更新第九版
But your health decisions are the same. Every time you have a carrot instead of a cookie, every time you go to the gym instead of going to the movies, that's a costly investment in your health. But how much you want to invest is going to depend on how much longer you expect to live in the future, even if you don't make those investments. AIDS is the same kind of thing. It's costly to avoid AIDS. People really like to have sex. But, you know, it has a benefit in terms of future longevity. But life expectancy in Africa, even without AIDS, is really, really low: 40 or 50 years in a lot of places. I think it's possible, if we think about that intuition, and think about that fact, that maybe that explains some of this low behavior change.
而健康也是如此 每次放棄餅乾而去吃胡蘿蔔時 每次去健身房而不是看電影時 就是你對健康極大的投資 但你要投資多少 跟你能活多久有關 有沒有投資都一樣 愛滋病也是如此,防疫愛滋也是昂貴的 大家都喜歡做愛 以未來長壽來講,它確實有好處 但在非洲,即使沒有愛滋病,平均壽命還是很低 大部分地方是40到50歲 這樣可以馬上理解 低行為改變的原因了
But we really need to test that. And a great way to test that is to look across areas in Africa and see: do people with more life expectancy change their sexual behavior more? And the way that I'm going to do that is, I'm going to look across areas with different levels of malaria. So malaria is a disease that kills you. It's a disease that kills a lot of adults in Africa, in addition to a lot of children. And so people who live in areas with a lot of malaria are going to have lower life expectancy than people who live in areas with limited malaria. So one way to test to see whether we can explain some of this behavior change by differences in life expectancy is to look and see is there more behavior change in areas where there's less malaria.
但仍需要證實 證實的方法就是,看非洲地區 平均壽命高的地方,性行為是否有較大的改變? 我的作法是 調查不同程度的瘧疾地區 瘧疾也是會致命的疾病 在非洲,無數的大人、小孩因此死亡 所以住在瘧疾病率高地區的人 平均壽命低於瘧疾不嚴重地區的人 所以我們研究 壽命是否會影響行為改變的方法 就是觀察瘧疾病率低的地區 是否有較大的行為改變
So that's what this figure shows you. This shows you -- in areas with low malaria, medium malaria, high malaria -- what happens to the number of sexual partners as you increase HIV prevalence. If you look at the blue line, the areas with low levels of malaria, you can see in those areas, actually, the number of sexual partners is decreasing a lot as HIV prevalence goes up. Areas with medium levels of malaria it decreases some -- it doesn't decrease as much. And areas with high levels of malaria -- actually, it's increasing a little bit, although that's not significant.
這是我們的數據 分別是低、中、高程度瘧疾病率的地區 當愛滋病毒傳播增加時,性伴侶的數量情形 看這條藍線 在這些瘧疾較少的地區 當愛滋病毒傳播率提高時 性伴侶數量是大量減少的 中程度瘧疾地區 雖然也有減少但不明顯,高程度瘧疾地區 反而增加,雖然數目不大
This is not just through malaria. Young women who live in areas with high maternal mortality change their behavior less in response to HIV than young women who live in areas with low maternal mortality. There's another risk, and they respond less to this existing risk.
還不只是瘧疾 高產婦死亡率地區的年輕婦女 為了防止愛滋病毒所做的行為改變 比低產婦死亡率地區的年輕婦女還少 因為有其他風險,所以他們對於已知風險的反應不大
So by itself, I think this tells a lot about how people behave. It tells us something about why we see limited behavior change in Africa.
這解釋了許多人類的行為 像是為什麼非洲的行為改變有限
But it also tells us something about policy. Even if you only cared about AIDS in Africa, it might still be a good idea to invest in malaria, in combating poor indoor air quality, in improving maternal mortality rates. Because if you improve those things, then people are going to have an incentive to avoid AIDS on their own. But it also tells us something about one of these facts that we talked about before. Education campaigns, like the one that the president is focusing on in his funding, may not be enough, at least not alone. If people have no incentive to avoid AIDS on their own, even if they know everything about the disease, they still may not change their behavior.
但還有政策的成效 即使你只關心在非洲的愛滋病情況 一起投資改善瘧疾、 室內的空氣品質、 降低產婦死亡率也是很重要的 因為改變了這些 人們就會自覺性的防治愛滋病 這也證實我們先前所提的 總統一直投入資金的教育活動 是不夠的 如果他們沒有防治愛滋病的自覺 就算他們了解這疾病 還是不會改變他們的行為
So the other thing that I think we learn here is that AIDS is not going to fix itself. People aren't changing their behavior enough to decrease the growth in the epidemic. So we're going to need to think about policy and what kind of policies might be effective.
我們知道愛滋不會自癒 就算人們改變行為 傳染率降幅也不大 我們要重新考慮政策 找出更有效的政策
And a great way to learn about policy is to look at what worked in the past. The reason that we know that the ABC campaign was effective in Uganda is we have good data on prevalence over time. In Uganda we see the prevalence went down. We know they had this campaign. That's how we learn about what works. It's not the only place we had any interventions. Other places have tried things, so why don't we look at those places and see what happened to their prevalence?
了解政策的方法,可以從過去的情形來看 我們知道,ABC運動 在烏干達這麼有效的原因,是因為當時有數據 可以看出傳染率下降 我們知道是ABC運動的關係,所以做出此結論 但不只有烏干達有活動 其他地方也有政策,那我們怎麼 不看看那些地方的情形呢?
Unfortunately, there's almost no good data on HIV prevalence in the general population in Africa until about 2003. So if I asked you, "Why don't you go and find me the prevalence in Burkina Faso in 1991?" You get on Google, you Google, and you find, actually the only people tested in Burkina Faso in 1991 are STD patients and pregnant women, which is not a terribly representative group of people. Then if you poked a little more, you looked a little more at what was going on, you'd find that actually that was a pretty good year, because in some years the only people tested are IV drug users. But even worse -- some years it's only IV drug users, some years it's only pregnant women. We have no way to figure out what happened over time. We have no consistent testing.
不幸的,我們並沒有2003年 非洲普遍人口的愛滋病毒感染情形 所以如果要找布基那法索國 1991年傳染率數據 用Google查一下,你會發現 1991年布基那法索國受測者 都是性病患者和懷孕婦女 這群受測對象還可以 但如果深入調查,你會發現 當年的結果是不錯的 其他年的受測對象都是靜脈藥癮者 更糟的是,有些年是測靜脈藥癮者 有些年只有測懷孕婦女 根本無法得知當時情形 也沒有持續抽樣檢察
Now in the last few years, we actually have done some good testing. In Kenya, in Zambia, and a bunch of countries, there's been testing in random samples of the population. But this leaves us with a big gap in our knowledge. So I can tell you what the prevalence was in Kenya in 2003, but I can't tell you anything about 1993 or 1983.
但幾年後,我們確實做了一些抽檢 在肯亞、尚比亞和一些國家 都有一些隨機抽樣 但數據上還是留了很大一片空白 我能告訴你,肯亞2003年的感染情況 但我無法提供1993年或1983年的情況
So this is a problem for policy. It was a problem for my research. And I started thinking about how else might we figure out what the prevalence of HIV was in Africa in the past. And I think that the answer is, we can look at mortality data, and we can use mortality data to figure out what the prevalence was in the past.
這是政策的問題,也是我研究遇到的問題 所以我開始想其他可能的辦法 以獲得非洲過去的愛滋病毒傳染率數據 我想到的方法是,利用死亡率數據 來算出過去的愛滋病毒傳染率
To do this, we're going to have to rely on the fact that AIDS is a very specific kind of disease. It kills people in the prime of their lives. Not a lot of other diseases have that profile. And you can see here -- this is a graph of death rates by age in Botswana and Egypt. Botswana is a place with a lot of AIDS, Egypt is a place without a lot of AIDS. And you see they have pretty similar death rates among young kids and old people. That suggests it's pretty similar levels of development.
所以我們只能用愛滋病 有個獨特性- 會在人類黃金時期致死-這點 其他疾病都沒有這個特點,所以可以看到: 這是波紮那和埃及的死亡率,以年齡劃分 波紮那是愛滋盛行的地區 埃及是愛滋不盛行的地區 他們的兒童、老人死亡率相似 表示他們有相似的發展水準
But in this middle region, between 20 and 45, the death rates in Botswana are much, much, much higher than in Egypt. But since there are very few other diseases that kill people, we can really attribute that mortality to HIV. But because people who died this year of AIDS got it a few years ago, we can use this data on mortality to figure out what HIV prevalence was in the past. So it turns out, if you use this technique, actually your estimates of prevalence are very close to what we get from testing random samples in the population, but they're very, very different than what UNAIDS tells us the prevalences are.
但在20到45歲間的死亡率 波紮那死亡率高出埃及很多 但其他會致死的並不多 我們能將死亡率歸因為愛滋 但愛滋感染到死亡的期間很長 我們就用死亡率推回幾年前愛滋傳染率 所以,用這方法 我們能估算,受測結果 與估計的愛滋傳染率是很接近的 但卻與聯合國愛滋病規劃署(UNAIDS)提供的數據大不相同
So this is a graph of prevalence estimated by UNAIDS, and prevalence based on the mortality data for the years in the late 1990s in nine countries in Africa. You can see, almost without exception, the UNAIDS estimates are much higher than the mortality-based estimates. UNAIDS tell us that the HIV rate in Zambia is 20 percent, and mortality estimates suggest it's only about 5 percent. And these are not trivial differences in mortality rates. So this is another way to see this. You can see that for the prevalence to be as high as UNAIDS says, we have to really see 60 deaths per 10,000 rather than 20 deaths per 10,000 in this age group.
這是UNAIDS的傳染率統計 以及1990年後期非洲九國 的死亡率數據 可以看出,幾乎沒有例外 UNAIDS的估計高出死亡率估計許多 UNAIDS說尚比亞愛滋傳播率20% 但死亡率估計只有5% 這種差距是很大的 從另一方向來看 如果傳播率有UNAIDS說的這麼高 那死亡率應為1萬名中有60人死亡 而不是1萬名有20人死亡的比例
I'm going to talk a little bit in a minute about how we can use this kind of information to learn something that's going to help us think about the world. But this also tells us that one of these facts that I mentioned in the beginning may not be quite right. If you think that 25 million people are infected, if you think that the UNAIDS numbers are much too high, maybe that's more like 10 or 15 million. It doesn't mean that AIDS isn't a problem. It's a gigantic problem. But it does suggest that that number might be a little big. What I really want to do, is I want to use this new data to try to figure out what makes the HIV epidemic grow faster or slower.
我想用一分鐘稍微來談 我們要怎麼用這種知識 來解決現有的問題 我也會談到,演講開始時 提到的某一點,其實是錯誤的 如果250萬人感染, 或者UNAIDS估計太高, 那說... 100-150萬好了 這樣估計不表示愛滋不是問題,愛滋很嚴重 但這表示數字有點灌水了 我希望做的是,利用這新數據 來解答愛滋病毒傳播快慢的原因
And I said in the beginning, I wasn't going to tell you about exports. When I started working on these projects, I was not thinking at all about economics, but eventually it kind of sucks you back in. So I am going to talk about exports and prices. And I want to talk about the relationship between economic activity, in particular export volume, and HIV infections.
如我一開始說的,我不談進出口 但我做了一些計畫 雖然不是以經濟為出發點 但最後總會回到經濟來 我要說的是進出口價格 各國的經濟活動、出口量以及 愛滋病毒感染的關係
So obviously, as an economist, I'm deeply familiar with the fact that development, that openness to trade, is really good for developing countries. It's good for improving people's lives. But openness and inter-connectedness, it comes with a cost when we think about disease. I don't think this should be a surprise. On Wednesday, I learned from Laurie Garrett that I'm definitely going to get the bird flu, and I wouldn't be at all worried about that if we never had any contact with Asia.
身為經濟學家,我明白 對於發展中國家來說 出口發展、自由是很重要的 可以促進生活品質 但以疾病角度來說 這種自由與交流是有代價的 星期三,蓋瑞特(全球衛生研究員)說 我一定會得禽流感 但要是我們和亞洲沒有接觸 根本不必擔心
And HIV is actually particularly closely linked to transit. The epidemic was introduced to the US by actually one male steward on an airline flight, who got the disease in Africa and brought it back. And that was the genesis of the entire epidemic in the US. In Africa, epidemiologists have noted for a long time that truck drivers and migrants are more likely to be infected than other people. Areas with a lot of economic activity -- with a lot of roads, with a lot of urbanization -- those areas have higher prevalence than others.
而愛滋病毒與運輸是緊密相連的 愛滋當時傳到美國 其實是因為飛機上一名男空服員 從非洲將病毒帶回來 也是美國愛滋病的開端 在非洲,病理學家很早之前就發現 移民者、卡車司機的感染率高於其他人 如果該地有很多經濟活動、 很多道路、非常都市化 那麼傳染率則較普及
But that actually doesn't mean at all that if we gave people more exports, more trade, that that would increase prevalence. By using this new data, using this information about prevalence over time, we can actually test that. And so it seems to be -- fortunately, I think -- it seems to be the case that these things are positively related. More exports means more AIDS. And that effect is really big. So the data that I have suggests that if you double export volume, it will lead to a quadrupling of new HIV infections.
但也不代表 如果有更多交易、出口,就會增加感染率 利用這個傳染率的數據 我們可以測試看看 結果證明是對的 這些東西是相互關聯的 越多出口、越多愛滋,影響極大 數據顯示,如果出口數加一倍 愛滋感染率會增加四倍
So this has important implications both for forecasting and for policy. From a forecasting perspective, if we know where trade is likely to change, for example, because of the African Growth and Opportunities Act or other policies that encourage trade, we can actually think about which areas are likely to be heavily infected with HIV. And we can go and we can try to have pre-emptive preventive measures there. Likewise, as we're developing policies to try to encourage exports, if we know there's this externality -- this extra thing that's going to happen as we increase exports -- we can think about what the right kinds of policies are.
因此在預測、政策上都要將此納入考量 從預測的角度來看,如果我們知道交易會改變 例如,因為「非洲成長及機會法案」 或其他鼓勵交易的法案 我們可以知道這些地方感染率會提高 那就可以先發製人,做出因應措施 相同的,現在許多政策都鼓勵出口 如果我們知道會有外部效應- 增加出口連帶其他事情的發生 即可想出正確的因應政策
But it also tells us something about one of these things that we think that we know. Even though it is the case that poverty is linked to AIDS, in the sense that Africa is poor and they have a lot of AIDS, it's not necessarily the case that improving poverty -- at least in the short run, that improving exports and improving development -- it's not necessarily the case that that's going to lead to a decline in HIV prevalence.
有些事我們早已清楚 即使我們知道愛滋與貧窮習習相關 非洲窮、愛滋多 短期來說,不表示改善經濟 改善出口、改善當地發展 就能有效的 降低愛滋病毒盛行率
So throughout this talk I've mentioned a few times the special case of Uganda, and the fact that it's the only country in sub-Saharan Africa with successful prevention. It's been widely heralded. It's been replicated in Kenya, and Tanzania, and South Africa and many other places. But now I want to actually also question that. Because it is true that there was a decline in prevalence in Uganda in the 1990s. It's true that they had an education campaign. But there was actually something else that happened in Uganda in this period.
剛剛我重複提了 烏干達成功的案例 它是撒哈拉以南非洲唯一成功預防傳染的國家 結果大家都開心 相同政策也在肯亞、坦尚尼亞、南非等國實施 但我懷疑它的成效 因為1990年代,烏干達愛滋傳播率降低 一半是因為有教育性的活動 但事實上,烏干達當時發生了一件事
There was a big decline in coffee prices. Coffee is Uganda's major export. Their exports went down a lot in the early 1990s -- and actually that decline lines up really, really closely with this decline in new HIV infections. So you can see that both of these series -- the black line is export value, the red line is new HIV infections -- you can see they're both increasing. Starting about 1987 they're both going down a lot. And then actually they track each other a little bit on the increase later in the decade.
就是咖啡價格降低 烏干達主要出口是咖啡 1990年代早期,出口是下降的,可以看出 下降幅度與愛滋病毒感染幅度極為相同 可以從圖上明顯看出 黑線是出口數,紅線是愛滋病毒感染率 兩個都增加 從1987年開始,大幅下滑 最後幾年 兩個數據又同時上升
So if you combine the intuition in this figure with some of the data that I talked about before, it suggests that somewhere between 25 percent and 50 percent of the decline in prevalence in Uganda actually would have happened even without any education campaign.
所以用你的直覺以及 利用我剛剛的數據可以看出 烏干達傳染率的下降 有25%到50% 就算沒有教育活動也會減少
But that's enormously important for policy. We're spending so much money to try to replicate this campaign. And if it was only 50 percent as effective as we think that it was, then there are all sorts of other things maybe we should be spending our money on instead. Trying to change transmission rates by treating other sexually transmitted diseases. Trying to change them by engaging in male circumcision. There are tons of other things that we should think about doing. And maybe this tells us that we should be thinking more about those things.
這對於後來政策制定很重要 我們花了這麼多錢投入ABC運動 但只有我們預期一半的效果 所以或許我們應該 想想更多錢應該怎麼花的方法 像是治療其他性傳染疾病還控制傳染率 像是鼓勵男性割包皮 還有更多的事可以做 我想說的是,希望大家能想些其他能做的事
I hope that in the last 16 minutes I've told you something that you didn't know about AIDS, and I hope that I've gotten you questioning a little bit some of the things that you did know. And I hope that I've convinced you maybe that it's important to understand things about the epidemic in order to think about policy.
我希望剛剛16分鐘內,我分享了你們所不知道的事 我希望各位能深入思考 那些你們已知的事 我希望我成功說服你們 思考政策時 了解疾病是很重要的
But more than anything, you know, I'm an academic. And when I leave here, I'm going to go back and sit in my tiny office, and my computer, and my data. And the thing that's most exciting about that is every time I think about research, there are more questions. There are more things that I think that I want to do. And what's really, really great about being here is I'm sure that the questions that you guys have are very, very different than the questions that I think up myself. And I can't wait to hear about what they are. So thank you very much.
但是,我是一個學者 當演講結束,我會回到 我的小辦公室,對著我的電腦、數據 而我最興奮的事 我每次想到研究,我就會有更多的問題 我想做的還有很多 能來這裡真的很棒 我相信你們所思考的問題 都和我所想出的問題截然不同 而我非常期待你們想出的問題 謝謝大家