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The speaker reflects on a paper they wrote 40 years ago while still a student, which is associated with their master's thesis. The paper gained notoriety for addressing non-stationary time series modeling, revealing a correct approach that gained attention in the research community—building upon prior, less recognized work. The paper primarily focused on modeling economic relationships between consumption, income, and other variables.

A key contribution was the concept of cointegration, originally popularized by Clive Granger, which allows non-stationary variables to be analyzed by transforming them into stationary combinations. The speaker's study compared various methodologies and highlighted discrepancies in results among different research approaches, particularly emphasizing the importance of using both levels and differences of non-stationary variables in modeling.

The paper suggested using growth rates and included economic theory, particularly the savings ratio, in its regression analysis. While initially seen as ad hoc, the approach ultimately showed robust predictive power over the years, maintaining relevance even as new data emerged.

The speaker notes that while their original understanding was limited, subsequent developments in macroeconomic research significantly expanded the framework of cointegration, leading to its acceptance as a crucial tool for analyzing economic data.

In summary, the discussion emphasizes the evolution of thinking about time series data in economics, the enduring impact of the speaker's research, and the broader implications for macroeconomic modeling techniques in light of the rational expectations revolution.

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Here are some similar articles or topics that resonate with the themes and concepts presented in the video:

1. **Cointegration and Economic Time Series Analysis**:
- Articles discussing the development and application of cointegration in economic modeling, particularly those referencing the works of Clive Granger and his contributions to econometrics.

2. **Non-Stationary Time Series Models**:
- Research papers focused on the methodologies for modeling non-stationary time series data, including various techniques to address issues related to spurious regression, and the importance of differentiating between levels and differences.

3. **Historical Perspective on Macroeconomic Modeling**:
- Discussions on the historical evolution of macroeconomic models, including foundational ideas pre- and post-rational expectations revolution, explaining how these shifts have impacted current modeling practices.

4. **Comparative Methodologies in Time Series Analysis**:
- Studies that compare the effectiveness of different methodologies (OLS, ARIMA, VAR, etc.) in modeling economic variables, similar to how the speaker’s paper highlighted varying results from different approaches.

5. **The Savings Ratio and Economic Growth**:
- Research articles that delve into the relationship between savings ratios, consumption, and income, with a focus on their predictive capabilities in economic forecasts and growth theories.

6. **Advances in Macroeconomics: Rational Expectations and Beyond**:
- Papers discussing the implications of the rational expectations hypothesis on historical and contemporary economic models, elaborating on how economic agents’ expectations adjust to new information.

7. **Art of Predictive Modeling in Economics**:
- Articles that explore the art and science behind building predictive models in economics, emphasizing the importance of robust methodologies, model validation, and the role of theory in guiding empirical analysis.

8. **Evolution of Cointegration Techniques**:
- A review of how cointegration techniques have evolved since their inception, exploring new developments, applications, and extensions in various economic convideos.

By exploring these articles or topics, one can gain a deeper understanding of the themes related to time series modeling, cointegration, and their implications in macroeconomic research.

X-TIMESTAMP-MAP:LOCAL=00:00:00.000,MPEGTS=900000

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This paper was written 40 years ago, Joll early

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when I was still a student.

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At least in part not the work was done as part

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of my master's thesis, actually, or part of the work,

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although, it didn't come out in 1978.

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I graduated in 1975.

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So I've had a bit of fun rereading this

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after many, many years at your suggestion

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and thinking, what did we do there?

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And, of course, it is a bit notorious as this,

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this paper, and I can tell you why it's notorious,

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I think in, in a few words.

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Um, it's the, it, it really did for the first time,

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not quite the first time,

00:39.315 --> 00:43.235
because my other teacher, Dennis Saga, because my co-author

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and mentor was David Hendry with this paper at,

00:46.275 --> 00:47.955
this is at the London School of Economics.

00:48.055 --> 00:51.155
Dennis Sagan had something similar in the paper 10 years

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previously, but nobody really noticed it.

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It was asked that caught the attention of the,

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the research community.

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And this was to discover the correct way

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of modeling non stationary time series,

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because it had been done in the wrong way for,

01:10.885 --> 01:11.945
you know, quite a while.

01:12.125 --> 01:15.105
And one of the things that our paper does is

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to look at various examples of consumption, income

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regressions,

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with various dynamic aspects built into them.

01:25.005 --> 01:28.065
Of course, the, the person whose name one should mention,

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because he's, he is the one that got the Nobel Prize.

01:30.585 --> 01:34.625
He's Clive Granger because he, invented

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and popularized the notion of cointegration.

01:38.445 --> 01:40.145
And basically that's what we were doing.

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We were doing cointegration, but we didn't know it.

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All we knew was that we found an equation which,

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contained rates of change of the, in other words,

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the differences from year to year of our variables,

01:54.455 --> 01:58.305
consumption and income and inflation, and the price level

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and things of that kind as well as the levels.

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Of course, the levels are trending.

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The levels are aren't staying in one place.

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They're not, they're non stationary.

02:08.205 --> 02:11.665
But what five grains of notice was

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that if you look at linear combinations

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of non-stationary variables,

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the result can be a stationary process and

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therefore can be put into the same equation.

02:24.285 --> 02:27.225
Now, an something which I'd rather forgotten about,

02:27.225 --> 02:30.665
but it's a very important aspect of the paper, is

02:30.665 --> 02:32.945
that it compares different studies which

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are looking at the same, same times zero.

02:36.545 --> 02:39.665
It is the same problem with the same sort of economic theory

02:40.245 --> 02:41.945
in their minds,

02:41.965 --> 02:44.425
and yet really getting rather different results.

02:45.185 --> 02:49.405
And the particular paper, which was a, a curiosity to us,

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was, I forget the title

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and the names of the authors wall was one of them

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because that's how he is identified in, in, in,

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in our paper as wall.

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At wall at al.

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These people had been reading a, an important book

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by two chaps called Boxing Jenkins, who were not economists.

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They were concerned with modeling,

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statistical modeling of time series for purposes such

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as forecasting and,

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and, what they were ba their, their, their philosophy,

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which was really important as merging about the same sort

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of time, was that you could only really construct

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relationships between variables when they're all stationary.

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In other words, when they, when they have a a,

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a fixed distribution, they don't wander off in the same way

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that, things like stock prices

03:45.905 --> 03:49.125
and, GDP, you know, these things grow over time.

03:49.515 --> 03:52.485
Well, that doesn't do, you can't build,

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although that's what of course, economists were attempting

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to do and still do, attempt to do, you know, at times.

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But that we need to model stationary time series.

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And if they're not stationary, when we,

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when we receive the data,

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well then we don't look at the level,

04:07.625 --> 04:09.885
we look at the change from period to period,

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because that will usually appear stationary.

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And so, you know, the, the, these,

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these researchers were following, this,

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this line in which they were looking at the differences,

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the growth rates of consumption

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and the growth rate of income,

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and showing indeed that they were closely related.

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But of course, their relationship can't really tell you very

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much about what's going on in the heads of consumers

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because the levels have been taken out.

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They have difference. So they're following a statistical,

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optimality, path,

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and yet they're throwing away any contribution

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of economic theory.

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The puzzle was that their, their model seemed

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to fit the data better than all the models,

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which incorporated economic theory by,

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by having good savings ratios

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and, relationship between consumption

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and income, as, part of them.

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So what, where did that leave us?

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Where it left us was that we thought we've gotta

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basically stick to this important notion

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that we can only really model stationary variables using,

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using regression techniques.

05:25.105 --> 05:26.395
Okay? Um,

05:26.975 --> 05:31.225
but on the same time, we want to get the levels

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of the variables as well as the differences

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of the variables into the equation.

05:37.205 --> 05:40.705
How did we do that? And in fact, the truth is that this was,

05:41.125 --> 05:44.465
I recall when I did this in my master's thesis,

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I was very apologetic.

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I said, this is totally ad hoc and stupid,

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but look, if I put the difference,

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and this is in logarithms,

05:52.965 --> 05:54.825
so it's really the log of a ratio.

05:55.525 --> 05:58.165
If I, if I put the difference of the logs

05:58.165 --> 06:01.525
of these two variables, well, with a, you know, last year,

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you know, we put a lag on so that, so that we have the,

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you know, the, the direction of causation appropriate.

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Uh, then the difference looks stationary

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and the changes are stationary.

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So the whole equation fits the box

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and Jenkins, prescription

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of best fitting stationary data.

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Um, and

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yet we've included the savings ratio in the equation, which

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therefore we expect to have some predictive power.

06:32.465 --> 06:36.245
Um, if, if it, it's, if, if, you know, the way

06:36.355 --> 06:41.285
that consumers behave informs how these data came to be.

06:42.395 --> 06:45.495
Um, and so I think that's what the, you know, what is known

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as the daisy paper, 'cause it's DHS

06:47.975 --> 06:51.385
and Y, the authors, of whom I'm the D

06:51.445 --> 06:53.265
and H is David Henry.

06:53.885 --> 06:57.585
Um, the other guys were only involved in the revision

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to do some extra data, you know, some extra,

07:00.455 --> 07:01.465
data analysis.

07:01.565 --> 07:04.265
So, I think we have to say the, the first version

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of this paper was just Davidson and Henry.

07:06.405 --> 07:09.305
So that's, that's how it all came, came about.

07:10.445 --> 07:14.225
Um, but what we were basically doing was saying, okay,

07:14.285 --> 07:17.545
you know, we, we've, we've, we've resolved,

07:18.315 --> 07:19.945
we've explained the difference

07:19.945 --> 07:22.185
between these different studies by saying,

07:22.765 --> 07:25.905
got on the one hand, follow the, you know, the,

07:25.905 --> 07:27.345
the box of Jenkins prescription.

07:27.445 --> 07:29.945
On the other hand, get the theory in there

07:30.125 --> 07:31.385
by getting the levels and

07:31.385 --> 07:32.465
the relationship between the levels.

07:33.245 --> 07:36.535
But reading that paper, in retrospect, of course,

07:36.555 --> 07:39.175
we had no idea really what we were doing,

07:39.175 --> 07:42.015
because Clive Granger hadn't yet read it.

07:42.875 --> 07:44.815
And the con, you know, the relevant concepts

07:44.815 --> 07:46.055
didn't, didn't yet exist.

07:46.195 --> 07:50.135
And this was, what amazingly grew over

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the next 20 years

07:52.235 --> 07:56.505
or so of macroeconomics research,

07:57.035 --> 07:59.745
which was the whole, the whole notion of cointegration

07:59.775 --> 08:01.745
that you, you, you look at collections

08:01.745 --> 08:03.265
of non-stationary variables.

08:03.265 --> 08:06.185
You don't ask if they're correlated

08:06.815 --> 08:09.185
because that's a notion which is only really

08:09.585 --> 08:10.905
relevant to stationary data.

08:11.445 --> 08:13.465
You ask if they're cointegration, which means

08:13.465 --> 08:14.625
that they have common trends.

08:15.205 --> 08:18.705
If you take suitable linear combinations of them,

08:19.005 --> 08:22.665
you get a stationary series, which can then be correlated,

08:22.875 --> 08:27.225
which is not co correlated with the growth with the,

08:27.385 --> 08:29.585
with the variables measuring differences

08:29.585 --> 08:30.625
from period to period.

08:31.545 --> 08:34.705
Um, now our equation

08:35.965 --> 08:38.985
did roll well because it turned out that,

08:39.365 --> 08:41.905
it fitted the data pretty well, but it was quite stable.

08:42.145 --> 08:45.265
I, I, I, there were subsequent studies oath

08:45.325 --> 08:48.905
for at least the next 15 years, which really found,

08:49.365 --> 08:51.825
you know, in other words, with new data that hadn't been,

08:52.855 --> 08:55.325
hadn't occurred when we wrote the original play.

08:55.325 --> 08:57.005
But going up into the 1980s,

08:57.785 --> 08:59.125
and it still fitted pretty well.

08:59.125 --> 09:00.245
It broke down eventually.

09:00.405 --> 09:03.045
I forget exactly when, sometime in the nineties

09:03.075 --> 09:04.285
that it collapsed.

09:04.745 --> 09:09.245
Um, but, so what this was telling us

09:09.245 --> 09:13.525
that we were isolating some,

09:14.905 --> 09:18.665
regularities in the data, that it wasn't the kind

09:18.665 --> 09:20.705
of regression which breaks down as soon

09:20.705 --> 09:22.305
as you add a new observation

09:22.895 --> 09:24.505
that hadn't been used to fit it.

09:24.645 --> 09:26.545
And of course, this is the, this is the problem

09:26.575 --> 09:28.585
with many regressions is that they, you know,

09:28.585 --> 09:30.105
they fit the sample well enough

09:30.105 --> 09:33.665
because you fix them to do so, put in one variable

09:33.665 --> 09:36.025
or another, but as soon as you bring in some new data,

09:36.135 --> 09:38.065
then you know, the whole thing falls apart.

09:38.495 --> 09:41.865
Well, the daisy consumption function

09:42.645 --> 09:44.425
really did rather well in that respect.

09:44.965 --> 09:49.025
Um, and, and it was u it was widely used, for,

09:49.045 --> 09:51.705
you know, by forecasters something, something similar.

09:51.925 --> 09:54.065
The, the whole ever correction idea.

09:54.785 --> 09:57.025
'cause the, where the ever correction,

09:57.095 --> 09:59.625
terminology comes from is precisely

09:59.625 --> 10:04.105
that you've got the savings ratio as it lags, as one

10:04.105 --> 10:05.385
of the explanatory variables.

10:05.385 --> 10:08.025
So if this moves, if people find that the

10:08.585 --> 10:10.385
saving more than they,

10:10.735 --> 10:13.065
than they do normally do in the long term,

10:13.735 --> 10:16.505
because their incomes have hopefully risen

10:16.505 --> 10:19.025
and their consumption has remained according

10:19.025 --> 10:20.625
to their usual habits and,

10:20.725 --> 10:24.625
and, so, golly, look, we've,

10:24.625 --> 10:26.865
we've got all this cash, let's go out

10:26.865 --> 10:27.905
and spend it on something.

10:27.965 --> 10:29.905
But this is something that doesn't happen immediately.

10:29.965 --> 10:32.625
It happens with an, with some irregular lag.

10:33.045 --> 10:36.345
So, so hence the error correction is that we assume

10:36.345 --> 10:39.065
that people focus on, of course, this doesn't only apply

10:39.065 --> 10:41.705
to consumption, it applies to lots of things, you know,

10:41.705 --> 10:45.225
money stock and, and, and, and,

10:45.225 --> 10:49.185
likewise in financial data, of course, there's also

10:49.925 --> 10:53.625
an awful lot of research has been done over the 40 years

10:53.775 --> 10:57.825
following, our original contribution

10:58.365 --> 11:00.625
in which, you know, this, this phenomenon

11:00.625 --> 11:03.065
of cointegration has turned up in a lot of places.

11:03.965 --> 11:06.745
And so it's been regarded as, as,

11:06.805 --> 11:09.185
as quite an important contribution to

11:10.015 --> 11:13.305
macroeconomic research, a great deal of the effort

11:13.375 --> 11:16.185
that took place in the latter half of the 20th century,

11:16.285 --> 11:20.145
you could say, into, into macroeconomic modeling,

11:20.145 --> 11:25.025
rather collapsed because it was pointed out that,

11:25.365 --> 11:29.865
that expectations, had to be modeled in terms

11:29.885 --> 11:32.585
of a complete,

11:32.975 --> 11:36.345
macroeconomic system rather than, you know,

11:36.345 --> 11:38.225
being simple, simple projections and,

11:38.445 --> 11:41.185
and essentially that, that, that, that large

11:41.815 --> 11:44.625
macroeconomic models, weren't expected

11:44.645 --> 11:47.225
to work very well, which we didn't anticipate, I think,

11:47.225 --> 11:48.705
at the time that we wrote this paper.

11:48.925 --> 11:52.905
So, so, so what, what is known as the rational expectations

11:53.325 --> 11:56.445
Revolution, rather shot a hole in some of this work.

11:56.985 --> 11:58.365
But, I think

11:58.365 --> 12:03.125
nonetheless, cointegration has continued to be a,

12:03.905 --> 12:06.645
you know, an, you know, an important tool in the Armory

12:07.025 --> 12:10.365
for understanding, non-stationary variables.

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